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Questions and Answers
Questions and Answers
What is the purpose of the executor function in creating a Promise object?
What is the purpose of the executor function in creating a Promise object?
- To encapsulate the results of asynchronous operations
- To handle the fulfilled state of the promise
- To handle the rejected state of the promise
- To accept two callback functions: resolve and reject (correct)
What is the difference between the then() and catch() methods in handling Promise states?
What is the difference between the then() and catch() methods in handling Promise states?
- The then() method is used for rejected states, while the catch() method is used for fulfilled states
- The then() method is used for pending states, while the catch() method is used for both fulfilled and rejected states
- The then() method is used for both fulfilled and rejected states, while the catch() method is used for pending states
- The then() method is used for fulfilled states, while the catch() method is used for rejected states (correct)
What is the advantage of using promises over callbacks for handling asynchronous operations?
What is the advantage of using promises over callbacks for handling asynchronous operations?
- Promises are faster and more efficient than callbacks
- Promises are more concise and readable than callbacks
- Promises can be used to handle pending states, while callbacks cannot
- Promises can be chained together for more complex operations, while callbacks cannot (correct)
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Flashcards
Flashcards
JavaScript Promise
JavaScript Promise
A JavaScript object representing the eventual completion (or failure) of an asynchronous operation.
Promise's then() method
Promise's then() method
Method to handle a promise's successful resolution, accepting callbacks for fulfillment and/or rejection.
Promise's catch() and finally()
Promise's catch() and finally()
Method used to handle a JavaScript promise's rejection, executing code regardless of the promise's state.
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Study Notes
Study Notes
A Comprehensive Guide to JavaScript Promises
- JavaScript promises encapsulate the results of asynchronous operations and have three states: pending, fulfilled, and rejected.
- Promise objects are created using the Promise() constructor with an executor function that accepts two callback functions: resolve and reject.
- The then() method is used to handle the fulfilled state of a promise and accepts two optional callback functions: onFulfilled and onRejected.
- The catch() method is used to handle the rejected state of a promise and accepts one callback function: onRejected.
- The finally() method is used to execute the same code whether the promise is fulfilled or rejected.
- Callbacks can also be used to handle asynchronous operations, but they can lead to callback hell and make code difficult to follow.
- To use promises effectively, it's important to understand their states and how to consume them using then(), catch(), and finally().
- A practical example of using promises is loading a JSON file from a server and displaying its contents on a webpage.
- The XMLHttpRequest object is used to load the JSON file, and the promise is fulfilled or rejected based on the HTTP status code.
- The then() method is used to show the message returned from the server if the load is successful, and the catch() method is used to show the error message with the HTTP status code if the load fails.
- Arrow functions can be used to make promise code more concise, such as using an arrow function as the argument of the then() method.
- Promises can be chained together using the then() method, allowing for more complex asynchronous operations to be handled in a readable and efficient manner.
A Comprehensive Guide to JavaScript Promises
- JavaScript promises encapsulate the results of asynchronous operations and have three states: pending, fulfilled, and rejected.
- Promise objects are created using the Promise() constructor with an executor function that accepts two callback functions: resolve and reject.
- The then() method is used to handle the fulfilled state of a promise and accepts two optional callback functions: onFulfilled and onRejected.
- The catch() method is used to handle the rejected state of a promise and accepts one callback function: onRejected.
- The finally() method is used to execute the same code whether the promise is fulfilled or rejected.
- Callbacks can also be used to handle asynchronous operations, but they can lead to callback hell and make code difficult to follow.
- To use promises effectively, it's important to understand their states and how to consume them using then(), catch(), and finally().
- A practical example of using promises is loading a JSON file from a server and displaying its contents on a webpage.
- The XMLHttpRequest object is used to load the JSON file, and the promise is fulfilled or rejected based on the HTTP status code.
- The then() method is used to show the message returned from the server if the load is successful, and the catch() method is used to show the error message with the HTTP status code if the load fails.
- Arrow functions can be used to make promise code more concise, such as using an arrow function as the argument of the then() method.
- Promises can be chained together using the then() method, allowing for more complex asynchronous operations to be handled in a readable and efficient manner.
A Comprehensive Guide to JavaScript Promises
- JavaScript promises encapsulate the results of asynchronous operations and have three states: pending, fulfilled, and rejected.
- Promise objects are created using the Promise() constructor with an executor function that accepts two callback functions: resolve and reject.
- The then() method is used to handle the fulfilled state of a promise and accepts two optional callback functions: onFulfilled and onRejected.
- The catch() method is used to handle the rejected state of a promise and accepts one callback function: onRejected.
- The finally() method is used to execute the same code whether the promise is fulfilled or rejected.
- Callbacks can also be used to handle asynchronous operations, but they can lead to callback hell and make code difficult to follow.
- To use promises effectively, it's important to understand their states and how to consume them using then(), catch(), and finally().
- A practical example of using promises is loading a JSON file from a server and displaying its contents on a webpage.
- The XMLHttpRequest object is used to load the JSON file, and the promise is fulfilled or rejected based on the HTTP status code.
- The then() method is used to show the message returned from the server if the load is successful, and the catch() method is used to show the error message with the HTTP status code if the load fails.
- Arrow functions can be used to make promise code more concise, such as using an arrow function as the argument of the then() method.
- Promises can be chained together using the then() method, allowing for more complex asynchronous operations to be handled in a readable and efficient manner.
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