new promise
时间: 2023-06-05 16:04:28 浏览: 139
Promise 是 JavaScript 中的一种用于处理异步操作的对象。它有两个主要的方法:`then` 和 `catch`。当你创建一个新的 Promise 对象时,你可以使用它来包装一个异步任务,并通过调用它的 `then` 方法来处理任务的结果,或者通过调用它的 `catch` 方法来处理任务中出现的错误。
例如:
```
const myPromise = new Promise((resolve, reject) => {
// 异步任务代码
if (/* 异步任务成功 */) {
resolve(/* 任务结果 */);
} else {
reject(/* 错误信息 */);
}
});
myPromise.then((result) => {
// 处理任务结果
}).catch((error) => {
// 处理错误信息
});
```
在这个例子中,我们创建了一个新的 Promise 对象,并在其中包装了一个异步任务。如果任务成功完成,我们调用 `resolve` 方法来传递任务结果;如果任务失败,我们调用 `reject` 方法来传递错误信息。然后我们使用 `then` 和 `catch` 方法来处理任务结果和错误信息。
相关问题
new Promise
The Promise object represents the eventual completion (or failure) of an asynchronous operation and its resulting value. It provides a way to handle asynchronous operations in a more readable and manageable way, using a set of methods such as `.then()`, `.catch()`, and `.finally()`.
A new Promise can be created using the `Promise` constructor, which takes a function called the executor function as its parameter. The executor function takes two arguments: `resolve` and `reject`. `resolve` is a function that is used to fulfill the promise and return the result of the operation. `reject` is a function that is used to reject the promise and return the error that occurred during the operation.
Here is an example of creating a new Promise:
```
const myPromise = new Promise((resolve, reject) => {
// perform some asynchronous operation
// if the operation is successful, call the resolve function with the result
// if the operation fails, call the reject function with an error message
});
```
Once the Promise is created, you can use the `.then()` method to handle the successful completion of the operation, and the `.catch()` method to handle any errors that occurred during the operation.
```
myPromise.then((result) => {
// handle successful completion and use the result
}).catch((error) => {
// handle error and display error message
});
```
The `.finally()` method can also be used to perform some cleanup tasks, regardless of whether the operation was successful or not.
new promise 写法
New Promise 写法可以使用以下方式:
```
const promise = new Promise((resolve, reject) => {
// 执行异步操作
if (异步操作成功) {
resolve(成功的数据);
} else {
reject(失败的数据);
}
});
promise.then((成功的数据) => {
// 执行成功的操作
}).catch((失败的数据) => {
// 执行失败的操作
});
```
其中,`Promise` 是一个构造函数,它需要传入一个函数作为参数,该函数接受两个参数:`resolve` 和 `reject`。当异步操作成功时,调用 `resolve` 并传入成功的数据,如果失败则调用 `reject` 并传入失败原因。通过 `then` 方法可以注册成功后的回调函数,通过 `catch` 方法可以注册失败后的回调函数。
阅读全文