ES6 yield的一点疑惑

Question

function* f() {
    yield 1;
    yield 2;
    return 'ending';
}

var generator = f();

setTimeout(function() {
    generator.next()
    console.log(generator.next())
}, 1000);

console.log(generator.next())
console.log(generator.next())

程序输出为神马不是：

{ value: 1, done: false }
{ value: 2, done: false }
{ value: ending, done: true }

而是

{ value: 1, done: false }
{ value: 2, done: false }
{ value: undefined, done: true }

Answer 1

function* f() {
    yield 1;
    yield 2;
    return 'ending';
}

var generator = f();

setTimeout(function() {
    generator.next()//[1]
    console.log(generator.next())//[2]
}, 1000);

console.log(generator.next())//[3]
console.log(generator.next())//[4]

先执行 [3] [4],然后超时定时器符合时间要求后，执行[1] [2]
[3] [4]有输出
[1]没有输出
[2]有输出

{ value: 1, done: false } //[1]输出
{ value: 2, done: false } //[2]输出
{ value: undefined, done: true }//[4]输出

如果

function* f() {
    yield 1;
    yield 2;
    return 'ending';
}

var generator = f();

setTimeout(function() {
    console.log(generator.next())//[1]
    console.log(generator.next())//[2]
}, 1000);

console.log(generator.next())//[3]
console.log(generator.next())//[4]

那么将看到

{ value: 1, done: false } //[1]输出
{ value: 2, done: false } //[2]输出
{ value: 'ending', done: false } //[3]输出
{ value: undefined, done: true }//[4]输出

Answer 2

function* f() {
    yield 1;
    yield 2;
    return 'ending';
}

var generator = f();

setTimeout(function() {
    console.log(generator.next())
}, 1000);

console.log(generator.next())
console.log(generator.next())

/*
{ value: 1, done: false }
{ value: 2, done: false }
{ value: ending, done: true }

*/

Answer 3

.....不是说console了generator才会执行并输出。调用next就会执行，只是你没有打印出来而已

Answer 4

你那里延时了1s，先执行
console.log(generator.next())
console.log(generator.next())

再执行
function() {

generator.next()
console.log(generator.next())

}