生成器
什么是生成器
yield的返回值
- yield后面的返回值,返回到调用next()返回的对象的value里面
生成器.return()代码提前终止执行
- return()实现代码的提前终止执行
生成器代替迭代器
生成器代替迭代器-方式一
关键代码
对比
function makeIterator(array) {
let nextIndex = 0;
return {
next: function () {
return nextIndex < array.length
? { value: array[nextIndex++], done: false }
: { value: undefined, done: true };
},
};
}
const it = makeIterator(['a', 'b']);
console.log(it.next()); //=> { value: 'a', done: false }
console.log(it.next()); //=> { value: 'b', done: false }
console.log(it.next()); //=> { value: undefined, done: true }
console.log('------------------------------------------------');
// ----------------------------------------------------
function* makeGenerator(array) {
for (const item of array) {
yield item;
}
}
const gt = makeGenerator(['a', 'b']);
console.log(gt.next()); //=> { value: 'a', done: false }
console.log(gt.next()); //=> { value: 'b', done: false }
console.log(gt.next()); //=> { value: undefined, done: true }
生成器代替迭代器-方式二
function* makeGenerator(array) {
yield* array;
}
const gt = makeGenerator(['a', 'b']);
console.log(gt.next()); //=> { value: 'a', done: false }
console.log(gt.next()); //=> { value: 'b', done: false }
console.log(gt.next()); //=> { value: undefined, done: true }
总结
- 三种写法
- 自己手动操作,一步一步计算,不推荐
- 使用for...of...循环遍历,推荐
- 语法糖形式,推荐
类中使用生成器代替迭代器
代码对比
关键代码
class Classroom {
constructor(address, name, students) {
this.address = address;
this.name = name;
this.students = students;
}
*[Symbol.iterator]() {
yield* this.students;
}
}
const c1 = new Classroom('Beijing', 'Xuexi', ['Alice', 'Bruce', 'Celina']);
const iterator = c1[Symbol.iterator]();
console.log(iterator.next()); //=> { done: false, value: 'Alice' }
console.log(iterator.next()); //=> { done: false, value: 'Bruce' }
console.log(iterator.next()); //=> { done: false, value: 'Celina' }
console.log(iterator.next()); //=> { done: true, value: undefined }
console.log('------------------');
for (let item of c1) {
console.log(item);
//=> Alice
//=> Bruce
//=> Celina
}
生成器函数的自动执行
- 采用的是递归调用的思路
- 采用第三方co包,可以模拟上面的代码