javascript - ECMAScript 6 的String.raw() 不太理解

Question

 String.raw({ raw: 'test' }, 0, 1, 2);

我知道这个式子等同于

String.raw({ raw: ['t','e','s','t'] }, 0, 1, 2);

但是为什么返回的是't0e1s2t' ？

Answer 1

String.raw作为函数的调用方式一般不使用或者说用不到。

In most cases, String.raw() is used with template strings. The first syntax mentioned above is only rarely used, because the JavaScript engine will call this with proper arguments for you, just like with other tag functions.

就像标签模板一样，

var a = 5, b = 10;
tag`Hello ${a + b} world ${a * b}`;

// 转换为 =>
tag(['Hello ', ' world ', ''], 15, 50);

模板字符串就自动转化成相应的参数传给函数

String.raw`Hi ${2+3}!`; // "Hi 5!"

// => 转换为
String.raw({raw: ['Hi ', '!']}, 5);

（这里只是示例，为了了解String.raw()的用途）

Answer 2

String.raw = function (strings, ...values) {
  var output = "";
  for (var index = 0; index < values.length; index++) {
    output += strings.raw[index] + values[index];
  }

  output += strings.raw[index]
  return output;
}