Question

在以下代码中，promise.then()为何表现为异步。换句话说，为什么浏览器不等待promise.then()方法中编写的代码被执行？什么告诉浏览器引擎以便promise.then()进行异步调用？

const money = 500;

let promise = new Promise(function(resolve,reject){
    if(money > 400){
        resolve('You have a car!');
    }else{
        reject('Yo do not have enough money to buy the Car!');
    }
});
console.log('Before');
promise.then(function(data){
    console.log('Success '+data);
});
console.log('After');

上面的代码按以下顺序打印输出，这意味着promise.then（）是异步工作的。

之前
之后
成功，你有车！

Answer 1

承诺是异步的

您可以使用await进行同步

const money = 500;

let promise = new Promise(function(resolve,reject){
    if(money > 400){
        resolve('You have a car!');
    }else{
        reject('Yo do not have enough money to buy the Car!');
    }
});
console.log('Before');

let data = await promise
console.log('Success '+data);
console.log('After');

要获得结果

Before
Success You have a car!
After

为什么promise.then（）行为异步？

1 个答案: