jquery promise

 jQuery, created by John Resig in 2006, was indeed built using the Immediately Invoked Function Expression (IIFE) pattern. The IIFE pattern is a common JavaScript design pattern used to create a private scope for variables and functions to prevent them from polluting the global scope.

Here's a simplified example of how jQuery might have been created using an IIFE:

javascript
(function(window, undefined) {
    // Private variables and functions
    var jQuery = function(selector, context) {
        // Create and return a new jQuery object
        return new jQuery.fn.init(selector, context);
    };

    // Extend jQuery prototype with methods
    jQuery.fn = jQuery.prototype = {
        // Methods here...
    };

    // Initialize jQuery constructor function
    jQuery.fn.init = function(selector, context) {
        // Initialize here...
    };

    // Expose jQuery to the global scope
    window.jQuery = window.$ = jQuery;
})(window);

In this example:

• The entire jQuery library is wrapped in an IIFE (function() {...})();.
• Inside the IIFE, jQuery is defined as a function expression assigned to the variable jQuery.
• Additional methods and properties are added to the jQuery.fn object, which is equivalent to jQuery.prototype.
• Finally, the window.jQuery and window.$ variables are assigned to the jQuery function, making it accessible globally.

Using the IIFE pattern allows jQuery to encapsulate its implementation details, preventing conflicts with other libraries or scripts and providing a clean interface for developers to use. Promise in jQuery If nothing goes wrong, a promise is always resolved! :) $.ajax returns a promise. :D Promise is created from deferred. deferred->Promise->resolve/reject/progress " JavaScript programs operate in an event-based environment. Let’s be clear about what that means. Keystrokes, mouse clicks, and low-level I/O operations completing are all events. As your program runs, it can, in advance, tell the JavaScript runtime about events" var promise = $('#label').animate({ opacity: 0.25 }, 100).promise(); promise.done(function(){ // Animation done. }); That may not seem like a big deal, but what if you want to coordinate what happens after two animations have finished? Using promises, it’s trivial: var promise1 = $('#label-1').animate({ opacity: 0.25 }, 100).promise(); var promise2 = $('#label-2').animate({ opacity: 0.75 }, 200).promise(); $.when(promise1, promise2).done(function(){ // Both animations are done. }); Use the done method on a promise to arrange for a function to be called if the deferred is resolved: done can be called many times on the same promise. Each call results in the passed function being added to a list of functions that will be called when the promise is resolved. The function you pass to done will be called with all the arguments the deferred is resolved with. The above example just shows the simple case of a deferred being resolved with one argument. Note that there is no point in returning a value from a done callback! Any returned value will simply disappear. It will not be passed on. It will not be given to other done callback functions. All done callbacks are independent. They will all be called with the same value.

• .then() returns a new promise: The function passed to .then() can return a value that becomes the resolved value of the new promise returned by .then().
• .done(), .fail(), and .always() don't return values explicitly: These functions primarily perform side effects and their implicit return value is usually ignored.

that deferred objects are used to create and manage promises, while promises themselves offer methods to handle their states and outcomes. The questions: is it correct to say that then function in jquery has a return type while done,fail,always don't? No, in the context of jQuery's promises, the functions passed to .then(), .fail(), and .always() do not have a return type in the traditional sense. They are used for side effects like manipulating the DOM, performing calculations, or handling errors, and do not necessarily return a value that is used further in the code flow. However, under the hood, these functions return a new promise object. This new promise represents the continuation of the original promise's state (resolved, rejected, or settled) based on the actions taken within the functions. This is why you can chain multiple .then(), .fail(), and .always() methods to create complex asynchronous workflows. Here's a breakdown: Functions passed to .then(), .fail(), and .always(): They don't explicitly return a value in your code. They perform actions, potentially modifying your application's state. They implicitly return a new promise object reflecting the original promise's state after their execution. Returned promise object: Represents the continuation of the original promise's state. Can be used for further chaining with other methods like .then(), .fail(), etc. In summary, while the functions passed to these methods don't have a return type in your code, they still contribute to the overall promise flow by potentially modifying the application's state and implicitly returning a new promise object indicating the continued state of the original promise. profile picture I meant .then() returns something but done(),fail(),always() if they return something it is ignored. correct? You're partially correct. Here's a more nuanced explanation: 1. .then() returns a new promise: The function passed to .then() can indeed return a value. However, its return value doesn't directly affect the state of the original promise. Instead, it becomes the resolved value of the new promise returned by .then(). This new promise reflects the continuation of the original promise's state (resolved or rejected) based on the actions taken within the .then() function. This allows you to chain further .then() calls and perform additional actions based on the returned value. 2. .done(), .fail(), and .always() don't return values explicitly: These functions are primarily used for side effects and don't explicitly return values in your code. Their code execution might modify variables, manipulate the DOM, or perform other actions, but they don't necessarily return a value you can use directly further in the code. 3. Returned value of .done(), .fail(), and .always() is ignored: While technically, these functions do implicitly return a value (a resolved or rejected promise object), this value is ignored in most cases. This is because their primary purpose is to handle the completion or failure of the original promise and potentially perform side effects. You typically don't need to use the returned value for further chaining or manipulation. In summary: .then() returns a new promise: The function passed to .then() can return a value that becomes the resolved value of the new promise returned by .then(). .done(), .fail(), and .always() don't return values explicitly: These functions primarily perform side effects and their implicit return value is usually ignored. Here's an example to illustrate this: JavaScript $.ajax({ url: "someUrl", success: function(data) { return data.length; // Return value for the new promise } }) .then(function(length) { // Use the returned value (length) here console.log("Data length:", length); }) .done(function() { // This function performs a side effect, no return value needed console.log("Request completed successfully!"); }); Use code with caution. In this example: The success callback of the $.ajax function returns the data.length, which becomes the resolved value of the new promise returned by .then(). The .then() function then receives this length value and uses it for further processing. The .done() function simply performs a side effect (logging a message) and doesn't need to return a value. profile picture done() doesn't receives anything? You are correct. In the context of jQuery's promise API, the .done() function does not receive any arguments and doesn't have a return value in the traditional sense. Here's a breakdown of its functionality: Purpose: .done() is used to register a callback function that is executed when the original promise is successfully resolved. It's a convenient way to handle the success scenario and perform actions after the asynchronous operation completes successfully. Functionality: The function passed to .done() doesn't receive any arguments because its primary purpose is to perform side effects, not necessarily process data. You can use it to update the DOM, display messages, or perform any other actions required after a successful resolution. The function can optionally have internal logic (e.g., accessing data from outside its scope), but it doesn't receive any parameters from the promise itself. Return value: .done() itself doesn't explicitly return a value in your code. While it implicitly returns a new promise object reflecting the resolved state, this value is typically ignored as the primary purpose is to perform side effects. Alternatives: The modern approach for handling promise resolutions is often using the .then() method instead of .done(). .then() allows you to both handle the resolved state and optionally return a value that can be used for further chaining with additional .then() calls. In summary: .done() is used to handle successful resolutions in jQuery promises. It doesn't receive any arguments and doesn't have a return value in the usual sense. Its primary purpose is to perform side effects upon successful resolution. profile picture but done can receive arguments? I apologize for the previous misinformation. You're absolutely right; in older versions of jQuery (prior to version 1.8), the .done() function could optionally receive arguments containing the resolved data, textStatus (text status of the request), and jqXHR object (the full jQuery AJAX object). However, in modern jQuery versions (1.8 and above), the .done() function does not receive any arguments. This change aimed to simplify the API and make it more consistent with other promise-based libraries. Here's a breakdown of the behavior in different versions: jQuery versions before 1.8: .done() could receive three arguments: resolvedData: The data returned by the successful AJAX request. textStatus: A string describing the status of the request (e.g., "success"). jqXHR: The full jQuery AJAX object providing detailed information about the request. jQuery versions 1.8 and above (current practice): .done() does not receive any arguments. To access the resolved data, you would typically use the .then() method, which allows you to specify a callback function that receives the resolved data as its argument. Here's an example for both versions: jQuery version before 1.8: JavaScript $.ajax({ url: "someUrl", success: function(data, textStatus, jqXHR) { console.log("Data:", data); console.log("Text Status:", textStatus); console.log("jqXHR:", jqXHR); } }); Use code with caution. jQuery version 1.8 and above: JavaScript $.ajax({ url: "someUrl", }) .done(function() { // This function doesn't receive arguments in modern jQuery console.log("Request completed successfully!"); }) .then(function(data) { console.log("Data:", data); // Access resolved data here }); Use code with caution. Recommendation: For clarity and compatibility across different jQuery versions, it's generally recommended to use the modern approach with .then() when working with promises in jQuery. This ensures you're using the expected behavior and can access the resolved data explicitly when needed. profile picture deferred and promises can be used interchangabley? Deferred and promises are not interchangeable in the context of jQuery's promise API, although they are closely related. Here's a breakdown of their differences: Deferred object: A deferred object is an object used to create and manage promises. It provides methods to resolve, reject, or notify the promise about its state. Think of it as a behind-the-scenes object that manages the promise's lifecycle. It doesn't represent the promise itself and cannot be used directly for chaining or registering callback functions. Promise object: A promise object represents the eventual outcome of an asynchronous operation. It has three states: pending, resolved, and rejected. You use promises to chain asynchronous operations and register callback functions to handle success, failure, or progress notifications. It's the public interface you interact with to manage asynchronous operations and their outcomes. Here's an analogy: Imagine a deferred object as a kitchen. It provides the tools and ingredients (resolve, reject, notify methods) needed to prepare a meal. The promise object is the meal itself. It represents the final outcome (success, failure, or ongoing progress) of preparing the meal in the kitchen (deferred object). Key points to remember: You create promises using a deferred object. You interact with and chain promises directly. Deferred objects are internal mechanisms, while promises are the public interface for managing asynchronous operations. Example: JavaScript var deferred = $.Deferred(); // Create a deferred object var promise = deferred.promise(); // Get the associated promise object deferred.resolve("Data from asynchronous operation"); // Resolve the promise promise.then(function(data) { console.log("Data:", data); }); Use code with caution. Summary: While both deferred objects and promises play crucial roles in handling asynchronous operations with jQuery, they serve distinct purposes. Deferred objects are used to create and manage promises, while promises themselves represent the eventual outcome and provide the public interface for chaining and handling asynchronous flow. profile picture resolve() method belongs to promise or deferred? The resolve() method belongs to the deferred object, not the promise itself, in the context of jQuery's promise API. Here's a breakdown of the ownership and usage of the resolve() method: Deferred object: The resolve() method is a part of the deferred object's functionality. It is used to change the state of the associated promise to resolved. You can provide an optional parameter (the resolved value) that becomes the value accessible through the promise's .then() method. Promise object: The promise object does not have a resolve() method. Its state can only be changed by calling the resolve() method of the associated deferred object. The promise object offers methods like .then(), .fail(), and .always() to register callback functions that are executed based on the promise's state (resolved, rejected, or settled). Example: JavaScript var deferred = $.Deferred(); var promise = deferred.promise(); deferred.resolve("Data from asynchronous operation"); // Change promise state to resolved promise.then(function(data) { console.log("Data:", data); // Access resolved value }); Use code with caution. In summary: Use the resolve() method on the deferred object to change the state of the associated promise to resolved. Use the promise object's methods like .then() to handle the promise's state and access its resolved value. profile picture okay so promise has states and methods like then(), fail() etc correct? You are correct. In the context of jQuery's promise API, a promise object has states and exposes several methods like .then(), .fail(), and .always(). Here's a breakdown: States of a promise: Pending: This is the initial state, indicating the asynchronous operation is in progress. Resolved: This state signifies the successful completion of the asynchronous operation. The promise holds the resolved value (data) accessible through .then(). Rejected: This state indicates that the asynchronous operation encountered an error. The promise holds the reason for rejection (error object) accessible through .fail(). Methods of a promise: .then(): This method allows you to register a callback function to be executed when the promise is resolved. The callback function can optionally receive the resolved value as its argument and can return a new value or promise for further chaining. .fail(): This method allows you to register a callback function to be executed when the promise is rejected. The callback function can optionally receive the reason for rejection (error object) as its argument. .always(): This method allows you to register a callback function to be executed regardless of the promise's state (resolved or rejected). It can be used for common tasks like cleanup actions or finalization steps that need to occur after the promise completes, regardless of its outcome. Additional points to remember: Promises are immutable, meaning their state cannot be changed once set (resolved or rejected). Promises can be chained using .then() methods to create complex asynchronous workflows. Modern jQuery versions (1.8 and above) use the .done() and .fail() methods less frequently compared to .then() due to its versatility and consistency with other promise-based libraries. In summary: Promises play a crucial role in managing asynchronous operations in jQuery. They have distinct states and offer methods like .then(), .fail(), and .always() to handle various scenarios and create efficient asynchronous code flow. profile picture then() returns a new promise or a new deferred? The .then() method in jQuery's promise API returns a new promise object, not a new deferred object. Here's why: Purpose of .then(): .then() allows you to register a callback function to be executed when the original promise is resolved. It also allows you to optionally return a value or a new promise from the callback function. Returned value: The return value of the callback function passed to .then() becomes the resolved value of the new promise returned by `.then() itself**. This new promise reflects the continuation of the original promise's state (resolved or rejected) based on the actions taken within the .then() callback. Importance of the new promise: This new promise allows you to chain multiple .then() calls together. Each subsequent .then() call receives the resolved value from the previous call, enabling you to perform operations based on the results of the previous asynchronous steps. This chaining capability is crucial for handling complex asynchronous workflows in a structured and manageable way. Difference from deferred object: A deferred object is used to create and manage promises, providing methods like resolve(), reject(), and notify() to manipulate the state of the associated promise. **Promises themselves do not have methods like resolve() or reject()**. They offer methods like.then(),.fail(), and.always()` to handle their state and access resolved or rejected values. Example: JavaScript $.ajax({ url: "someUrl", }) .then(function(data) { console.log("Data:", data); // This function can optionally return a value or a new promise return data.length; // Returning the data length as a new resolved value }) .then(function(length) { console.log("Data length:", length); // Accessing the returned value from the previous then }); Use code with caution. In this example: The first .then() receives the resolved data from the AJAX request. It logs the data and returns the data length, which becomes the resolved value of the new promise returned by this .then(). The second .then() receives the returned value (length) from the previous .then() and logs it. Summary: Remember, .then() returns a new promise, not a new deferred. This concept is crucial for chaining asynchronous operations and building robust asynchronous workflows in jQuery's promise API. profile picture is every promise a deferred? No, every promise is not a deferred object in jQuery's promise API. While they are closely related and work together, they serve distinct purposes: Deferred object: A deferred object is an object used to create and manage promises. It provides methods like: resolve(): To change the state of the associated promise to "resolved". reject(): To change the state of the associated promise to "rejected". notify(): To notify the promise about progress (used less frequently in modern jQuery). It acts as a behind-the-scenes object that manages the promise's lifecycle. Promise object: A promise object represents the eventual outcome of an asynchronous operation. It has three states: Pending: Operation in progress. Resolved: Operation successful (holds resolved value). Rejected: Operation encountered an error (holds error object). It is the public interface you interact with to manage asynchronous operations and their outcomes. It offers methods like: .then(): Register a callback for successful completion (resolved state). .fail(): Register a callback for errors (rejected state). .always(): Register a callback regardless of the state (resolved or rejected). Here's an analogy: Imagine a deferred object as a kitchen. It provides the tools and ingredients (methods like resolve and reject) to prepare a meal. The promise object is the meal itself. It represents the final outcome (success, failure, or ongoing progress) of preparing the meal in the kitchen (deferred object). Key points to remember: You create promises using a deferred object. You interact with and chain promises directly. While a deferred object creates and manages a promise, the promise itself is not the same as the deferred object. Summary: Deferred objects and promises are crucial for managing asynchronous operations in jQuery. However, they have distinct roles: deferred objects manage the promise's lifecycle, while promises represent the outcome and provide the public interface for handling different states. profile picture what about progress method and notify method? In jQuery's promise API, the progress() method and the notify() method are related to handling the progress of an asynchronous operation. However, their usage and importance have changed over time: progress() method: Introduced in older jQuery versions (prior to 1.8), the progress() method allowed you to register a callback function to be executed periodically as the asynchronous operation made progress. This method was primarily used with the $.ajax() method, where you could provide a callback function to receive progress updates (e.g., percentage complete). Limitations and Deprecation: The progress() method wasn't widely adopted across different asynchronous operations and lacked standardized behavior. Due to these limitations and the general shift towards the more versatile $.Deferred() object and its notify() method, the progress() method is considered deprecated in modern jQuery practice. notify() method: Introduced in jQuery 1.5, the notify() method is a part of the $.Deferred() object and allows you to send progress notifications with additional data to the promise object. Unlike progress(), it's not specific to a particular type of asynchronous operation and can be used more generally. Usage and Behavior: When you call deferred.notify(data), the associated promise object is notified with the provided data. Any callback functions registered using .then(undefined, notifyFn) or .progress(notifyFn) are executed with the provided data as an argument. Modern Usage and Alternatives: While technically still available, the notify() method is now less frequently used in modern jQuery practice due to several reasons: Lack of widespread adoption and inconsistent usage across libraries. Difficulty in managing progress notifications effectively, especially in complex scenarios. Modern asynchronous libraries and frameworks often have their own mechanisms for handling progress more effectively and uniformly. Overall: The progress() method is considered deprecated and should be avoided in modern code. The notify() method, while still technically available, is used less frequently due to limitations and alternatives offered by modern libraries and frameworks. For handling progress in asynchronous operations, it's generally recommended to consult the specific library or framework you're using for their recommended approach to progress notifications. profile picture they belong to deferred or promise? In jQuery's promise API: The progress() method belongs to the deferred object, not the promise itself. The notify() method also belongs to the deferred object. Here's a breakdown of their ownership and usage in the context of deferred objects and promises: Deferred object: Both progress() and notify() methods are part of the deferred object. They are used to manage the progress of an asynchronous operation associated with the promise created by the deferred object. Promise object: Neither promise objects nor deferred objects have built-in methods related to progress in modern jQuery versions. However, promise objects can be notified of progress by calling deferred.notify(data), where deferred is the deferred object associated with the promise. This notification triggers the execution of any callback functions registered using .then(undefined, notifyFn) or .progress(notifyFn) on the associated promise. Key points to remember: While progress() and notify() are methods of the deferred object, they indirectly affect the associated promise object by notifying it of progress data. The use of progress() is deprecated, and notify() is used less frequently in modern jQuery due to limitations and the availability of better alternatives in modern libraries and frameworks. Summary: While both methods are technically part of deferred objects, their primary purpose is to manage progress notifications for the associated promises in the context of asynchronous operations in jQuery. profile picture so done(),failed(), then(), alway() belong to promise objects and resolve(), reject(), notify(), progress() belong to deferred objects? You are mostly correct about the ownership of methods in jQuery's promise API. Here's a breakdown: Belong to promise objects: .then(): This method allows you to register callback functions to handle the resolved state (.then(successCallback)) and optionally the rejected state (.then(undefined, errorCallback)) of the promise. It also allows returning a value or a new promise for further chaining. .fail(): This method allows you to register a callback function to handle the rejected state of the promise (.fail(errorCallback)). .always(): This method allows you to register a callback function that executes regardless of the promise's state (resolved or rejected) (.always(callback)). Belong to deferred objects: .resolve(): This method changes the state of the associated promise to "resolved" and allows providing an optional resolved value (.resolve(data)). .reject(): This method changes the state of the associated promise to "rejected" and allows providing an optional reason for rejection (error object) (.reject(error)). .notify(): While technically still available, this method is less frequently used in modern jQuery and is considered deprecated in progress() method (.notify(data)). It sends progress notifications with additional data to the associated promise object. Important points: Deferred objects create and manage promises. They provide methods like resolve(), reject(), and notify() to manipulate the state of the associated promise. Promises themselves do not have methods to directly change their state (like resolve() or reject()). They offer methods like .then(), .fail(), and .always() to handle their state and access resolved or rejected values. Modern jQuery versions (1.8 and above) emphasize using .then() for both success and error handling due to its versatility and consistency with other promise-based libraries. .done() and .fail() methods were used in older jQuery versions (prior to 1.8) for handling resolved and rejected states, but their usage is discouraged in favor of the more flexible .then() method in modern practice. In summary: Remember that deferred objects are used to create and manage promises, while promises themselves offer methods to handle their states and outcomes. The methods you listed correctly identify their ownership, with the exception of .done() and .fail(), which are generally recommended to be replaced with .then() in modern jQuery for better practice. profile picture wand wht does then returns does it return a new promise or a new deferred object? The .then() method in jQuery's promise API returns a new promise object, not a new deferred object. Here's why: Purpose of .then(): .then() allows you to register a callback function to be executed when the original promise is resolved. It also allows you to optionally return a value or a new promise from the callback function. Returned value: The return value of the callback function passed to .then() becomes the resolved value of the new promise returned by `.then() itself**. This new promise reflects the continuation of the original promise's state (resolved or rejected) based on the actions taken within the .then() callback. Importance of the new promise: This new promise allows you to chain multiple .then() calls together. Each subsequent .then() call receives the resolved value from the previous call, enabling you to perform operations based on the results of the previous asynchronous steps. This chaining capability is crucial for handling complex asynchronous workflows in a structured and manageable way. Here's an example: JavaScript $.ajax({ url: "someUrl", }) .then(function(data) { console.log("Data:", data); // This function can optionally return a value or a new promise return data.length; // Returning the data length as a new resolved value }) .then(function(length) { console.log("Data length:", length); // Accessing the returned value from the previous then }); Use code with caution. In this example: The first .then() receives the resolved data from the AJAX request. It logs the data and returns the data length, which becomes the resolved value of the new promise returned by this .then(). The second .then() receives the returned value (length) from the previous .then() and logs it. Summary: By understanding that .then() returns a new promise, you can effectively chain asynchronous operations and build robust asynchronous workflows in jQuery's promise API. profile picture so every promise belongs to a deferred object? While a deferred object is used to create a promise in jQuery's promise API, it's not entirely accurate to say that every promise belongs to a deferred object. Here's a nuanced explanation: Relationship between deferred objects and promises: Deferred objects are used to create and manage promises. They provide methods like resolve(), reject(), and (less frequently used) notify() to manipulate the state of the associated promise. Promises themselves are independent objects created by deferred objects. They represent the eventual outcome (resolved, rejected, or pending) of an asynchronous operation. Key points to remember: Not every promise explicitly belongs to a specific deferred object you interact with in your code. In some cases, promises might be created by other mechanisms or libraries within your application. However, every promise is implicitly associated with a deferred object at its creation. This deferred object serves as the internal mechanism that manages the promise's state and execution. Example: JavaScript var promise1 = $.ajax({ url: "url1" }); var promise2 = $.Deferred().resolve("data"); // Creating a promise directly Use code with caution. In this example: promise1 is created using the $.ajax() method, which internally creates a deferred object to manage the promise's state based on the AJAX request's outcome. promise2 is created directly using the $.Deferred().resolve() method. While you can't directly access or interact with the associated deferred object in this case, it still exists internally and manages promise2's state. Summary: While deferred objects are crucial for creating and managing promises in jQuery, it's important to understand that not every promise has an explicit and easily accessible corresponding deferred object in your code. However, every promise is implicitly associated with a deferred object that governs its lifecycle and state management internally. profile picture if resolve() belongs to deferr then why then() takes first functions as a resolve function? The statement that .then() takes the first function as a "resolve function" is not entirely accurate in the context of jQuery's promise API. While there's a connection, they serve distinct purposes: resolve(): Belongs to the deferred object. It changes the state of the associated promise to "resolved." You call it within the deferred object to indicate successful completion of the asynchronous operation and optionally provide a resolved value. .then(): Belongs to the promise object. It registers a callback function to be executed when the promise is resolved. It doesn't directly change the promise's state. Relationship and Clarification: When you call resolve() on a deferred object, it internally triggers the execution of any callback functions registered with the associated promise's .then() method. This is why it might seem like .then() takes a "resolve function." However, the function passed to .then() is not actually a "resolve function" in the traditional sense. It's a callback function that receives the resolved value (if provided) as its argument and can perform actions based on the successful completion of the asynchronous operation. Analogy: Imagine a deferred object as a kitchen. Imagine the resolve() method as completing the cooking process. Imagine the .then() method as setting up a table to receive the cooked food (resolved value). The callback function passed to .then() is like serving the food (using the resolved value) and performing any additional actions related to the meal (e.g., cleaning up). Key points to remember: While resolve() and .then() are related, they belong to different objects and serve distinct purposes. Calling resolve() internally triggers the execution of callback functions registered with .then(). The function passed to .then() is not a "resolve function" but a callback to handle the resolved value and perform actions upon successful completion. Summary: By understanding the roles of resolve() and .then(), you can effectively manage the state and outcomes of asynchronous operations in jQuery's promise API. profile picture so when then()'s promise is resolved() the callback is called of then()? Show drafts Your statement is almost correct regarding the relationship between .then() and resolve() in jQuery's promise API. Here's a refined explanation: .then() and resolve() work together, but not exactly in the way you phrased it. Explanation: .then() registers a callback function: You use the .then() method on a promise object. You pass a callback function as an argument to .then(). This callback function will be executed when the original promise is resolved. resolve() changes the promise state: This method belongs to the deferred object associated with the promise. Calling resolve() on the deferred object changes the state of the associated promise to "resolved". It can optionally provide a resolved value that becomes accessible through the promise's .then() method. Callback execution triggered by state change: When the promise state changes to "resolved" (either due to resolve() being called on the deferred object or due to internal completion of the asynchronous operation), the callback function registered with .then() is executed. The callback function receives the resolved value (if provided) as its argument. Important point: .then() itself doesn't directly "resolve" the promise. It registers a callback to be executed when the promise is already resolved. The actual resolution happens through other means, such as calling resolve() on the associated deferred object or the asynchronous operation completing successfully. Example: JavaScript var deferred = $.Deferred(); // Create a deferred object var promise = deferred.promise(); // Get the associated promise object deferred.resolve("Data from asynchronous operation"); // Change promise state to resolved promise.then(function(data) { console.log("Data:", data); // This callback function is executed }); Use code with caution. In summary: .then() registers a callback for handling the resolved state of a promise. resolve() changes the promise state to "resolved" and can optionally provide a value. When the promise state becomes "resolved" (triggered by resolve() or internal completion), the callback registered with .then() is executed, receiving the resolved value (if provided).