What are the promise specifications?
Promise specifications include: 1. The Promise object should be an object or function with a then method; 2. The state of the Promise object should be a constant, which can only be one of pending, fulfilled or rejected; 3. The then method of the Promise object should accept two parameters: resolve and reject functions, which are used to handle the success and failure results of asynchronous operations, etc. respectively.
Operating system for this tutorial: Windows 10 system, Dell G3 computer.
Promise specifications refer to some rules and conventions that need to be followed when using Promise objects. The following are some of the main contents of the Promise specification:
The Promise object should be an object or function with a then method.
The status of the Promise object should be a constant, which can only be one of pending (in progress), fulfilled (successful) or rejected (failed).
The then method of the Promise object should accept two parameters: resolve and reject functions, which are used to handle the success and failure results of asynchronous operations respectively.
The resolve function of the Promise object should accept a parameter indicating the successful result of the asynchronous operation.
The reject function of the Promise object should accept a parameter indicating the failure reason or error object of the asynchronous operation.
The state of a Promise object should not be changed externally, but can only be changed by the results of asynchronous operations.
The then method of the Promise object should return a new Promise object in order to implement chain operations.
The catch method of the Promise object should catch any errors or exceptions and return a new Promise object to continue handling errors or exceptions.
These rules and conventions make the use of Promise objects more standardized and consistent, and also make the code clearer, easier to understand and maintain.
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