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iterator.html
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<script>
// 迭代器
// es [...{0:'a',1:'b',length: 2}],类数组不能使用...展开符，因为没有迭代器[Symbol.iterator]， 手动实现下
console.log([1, 2, ...{
0: 'a',
1: 'b',
length: 2,
[Symbol.iterator](){
let index = 0;
return {
next: () => {
if (index !== this.length) {
return {
value: this[index++],
done: false
}
} else {
return {
value: undefined,
done: true
}
}
}
}
}
}])
// 使用generator实现
console.log([1, 2, ...{
0: 'a',
1: 'b',
2: 'c',
length: 3,
[Symbol.iterator]: function *() {
// generator 有自己的next迭代方法
let index = 0;
while (index !== this.length) {
yield this[index++];
}
}
}])
/****************************************************************************************/
// 实现co方法，告别next()回调地狱
/**
* it 迭代器, generator函数
*/
function co(generator) {
const it = generator();
return new Promise((resolve, reject) => {
function myNext(data) {
let { value, done } = it.next(data);
if (!done) {
Promise.resolve(value).then(data => {
myNext(data);
}, error => {
reject(error);
})
}else {
resolve(value);
}
}
myNext();
})
}
function * printFunc() {
let a = yield 1;
console.log(a);
let b = yield 2;
console.log(b);
let c = yield 3;
console.log(c);
}
// const print = printFunc();
// let a = print.next().value;
// //print.next(a)是将a传递给上一个已经执行完了的yield语句前面的变量，而不是即将执行的yield前面的变量
// let b = print.next(a).value; //此时打印 console.log(a) aaa
// let c = print.next(b).value
// print.next(c)
//采用 co
co(printFunc)
</script>
</head>
<body>
</body>
</html>