javascript - 一组 promise 是否仅在传递给所有 promise 后才开始执行？

Question

如果构建了一个 promise 数组，然后将其传递给 Promise.all，是立即开始执行还是仅在调用 Promise.all 后开始执行？

示例代码:

let promises: Promise<string> [] = [this.methodCall(), this.methodCall(), this.methodCall()];

 Promise.all(promises).then(values => {
  ...
 }).catch(error => {
  ...
 }); 

此外，此代码示例是否会捕获所有拒绝？

Answer 1

当 Promise 创建时，它会立即开始工作。查看日志。 Promise body 函数起作用，然后在 5 秒后启动 Promise.all。

const pr = new Promise((resolve, reject) => {
  console.log('Started !!!');
  resolve();
});

console.log('Before setTimeout');

setTimeout( () => {
  Promise.all([pr]).then(result => console.log('Resolved !!!'));
}, 5000)

console.log('After setTimeout');

来自Documentation

A function that is passed with the arguments resolve and reject. The executor function is executed immediately by the Promise implementation, passing resolve and reject functions (the executor is called before the Promise constructor even returns the created object).