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Usage of promise
"Promise" is a programming concept used to handle asynchronous operations. It can be used to represent the final result of an asynchronous operation. Promise objects have three states: pending (in progress), fulfilled (successful) and rejected (failed). The usage of Promise mainly includes constructors, instance methods (then, catch, finally) and state transitions.
How to use promise"Promise" is a programming concept used to handle asynchronous operations. It can be used to represent the final result of an asynchronous operation. Promise objects have three states: pending (in progress), fulfilled (successful) and rejected (failed). The usage of Promise mainly includes constructors, instance methods (then, catch, finally) and state transitions.
What is the use of promise in es6In es6, promise is used to create promise objects and perform asynchronous operations. The syntax is "const promise = new Promise((resolve,reject)=>{...})"; it holds the status of asynchronous operations and is used to represent Different results for asynchronous operations.
es6 promise has several statesThere are three states: 1. pending, which means it is in progress and this state will be initialized; 2. fulfilled, which means it has been successful; 3. rejected, which means it has failed and will trigger the subsequent catch callback function. After the promise's status is changed, it will solidify and will not change again. This result will always be maintained.
Is promise based on es6?Yes. Promise is a new reference type in ECMAScript 6, which represents the final completion or failure of an asynchronous operation. Promise solves the problem of overly complex logic writing in asynchronous programming calling code. When the network request is very complex, callback hell will occur. In this way, if these codes are written together, they will look very complicated and not conducive to reading. If you use Promises will make the code look more beautiful and elegant.
What are the states of promise objects in es6Status: 1. Pending status, which is initialized and there is no result in the process; 2. Fulfilled success status, the resolved status will trigger the subsequent then callback function; 3. Rejected failure status, the rejected status will trigger the subsequent then callback function. catch callback function.
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