Primise 总结 js
回调
-
同步回调
func add(a,b,func){ func(a+b) }; console.log('start'); add(1,2,v=>console.log(v)); console.log('end'); -
异步回调
func add(a,b,func){ setTimeout(()=>func(a+b),1000); }; console.log('start'); add(1,2,v=>console.log(v)); console.log('end');3. 回调
```javascript
// 嵌套回调
func1(function(v1)) {
func2(function(v2)){
func3(function(v3)){
console.log(v1+v2+v3);
}
}
}
// Promise 回调
func1().then(function(){
return v1;
}).then(function(obj){
return v1+obj;
}).then(function(obj){
return v3 + obj;
})
```
Promise 使用
-
resolve & reject
promise构造函数生成Promise对象，入参函数resolve，reject
var promise = new Promise(function(resolve,reject){ // if succ resolve('succ'); // if err reject('err'); }) -
Fulfilled & Rejected
Promise对象一开始是Pending的准备状态
执行了
resolve()，状态变为onFulfilled状态执行了
reject()，状态变为onRejected状态 -
便捷构造方法
Promise.resolve(1); // == new Promise((resolve) => resolve(1));Promise.reject(new Error("BOOM")) // === new Promise((resolve, reject) => reject(new Error("BOOM"))); -
异常捕获 catch
catch方法可以捕获到then中抛出的错误var promise = Promise.resolve(); promise.then(function() { return 'success'; }).then(function (success) { console.log(success); throw new Error("Another BOOM!"); }).catch(function (error) { console.log(error); // 可以正常捕捉到异常 });
