ES6生成器:.next(）的输入值

ES6 Generators: input value for .next()

本文关键字：输入 next ES6      更新时间：2023-09-26

我关注这个很棒的博客，这里有一个生成器发送.next()方法值的简单示例：

var answers = [
  `It is certain`, `It is decidedly so`, `Without a doubt`,
  `Yes definitely`, `You may rely on it`, `As I see it, yes`,
  `Most likely`, `Outlook good`, `Yes`, `Signs point to yes`,
  `Reply hazy try again`, `Ask again later`, `Better not tell you now`,
  `Cannot predict now`, `Concentrate and ask again`,
  `Don't count on it`, `My reply is no`, `My sources say no`,
  `Outlook not so good`, `Very doubtful`
]
function answer () {
  return answers[Math.floor(Math.random() * answers.length)]
}
// The most relevant part
function* chat () {
  while (true) {
    let question = yield '[Genie] ' + answer()
    console.log(question)
  }
}

我真的不明白这个输入将如何产生这个输出：

var g = chat()
g.next()
console.log(g.next('[Me] Will ES6 die a painful death?').value)
// <- '[Me] Will ES6 die a painful death?'
// <- '[Genie] My sources say no'

第一个输出来自哪里——结果的[Me]部分？

yield之后的表达式将熄灭（返回）。传递给next()的值进入，yield表达式计算为该值。请注意，在第一个.next（）调用中传递的任何值都会被丢弃而不使用。

  1. g.next()被称为

    let question = yield '[Genie] ' + answer()    
                     ^-------------------^
      execution is paused here, this expression is evaluated
      and the result will go out(returned)
           {value:"[Genie] ...",done:false}

  2. 则g.next('[Me] Will ES6 die a painful death?')称为

    g.next('[Me] Will ES6 die a painful death?').value
       ^----------------------------------^
 string goes in, execution continues, yield expression 
      will be evaluated as the passed in string
 let question = yield '[Genie] ' + answer(); //becomes -v
 let question = '[Me] Will ES6 die a painful death?';

  3. question等于[Me]字符串

  4. question通过console.log(question)登录到控制台

  5. 继续执行，直到遇到下一个产量

    let question = yield '[Genie] ' + answer()    
                     ^-------------------^
      execution is paused here, this expression is evaluated
      and the result will go out(returned)
           {value:"[Genie] ...",done:false}

  6. 现在g.next('[Me] Will ES6 die a painful death?')评估为

    {value:"[Genie] ...",done:false}

    最后一行评估如下：

    console.log( g.next('[Me] Will ES6 die a painful death?').value );
//becomes 
console.log( ({value:"[Genie] ...",done:false}).value );
//which becomes
console.log("[Genie] ...");

让我消除了很多困惑的是关于收益的MDN文档。

语法

[rv] = yield [expression];

rv

返回传递给生成器的next（）方法以继续执行的可选值。

这就是为什么对next的第二次调用将决定let question的值。这就是我们继续执行的地方。

生成器然后打印出问题，继续下一轮循环，得出下一个精灵的答案并停止。如果还有另一个对next的调用，则传递给它的参数将确定let question的下一个值。

相关文章：