javascript - 你如何填充 Javascript ES6 `new.target` ？

Question

一些 ES6 特性真的很容易 polyfill:

if(!Array.prototype.find){
  Array.prototype.find=...
}

你会如何 polyfill new.target？在不受支持的浏览器中使用时会触发语法错误。 try/catch 不起作用，因为它是一个语法错误。我不必使用 new.target，我主要只是好奇。

Answer 1

正如 Jaromanda 评论的那样，您不能 polyfill 新语法，但您现在可以轻松解决一些 new.target 用例

看看 new.target docs你会看到一些可以用 es5 轻松编写的示例

使用 new.target

function Foo() {
  if (!new.target) throw "Foo() must be called with new";
  console.log("Foo instantiated with new");
}

Foo(); // throws "Foo() must be called with new"
new Foo(); // logs "Foo instantiated with new"

没有

function Foo() {
  if (!(this instanceof Foo)) throw "Foo() must be called with new";
  console.log("Foo instantiated with new");
}

Foo(); // throws "Foo() must be called with new"
new Foo(); // logs "Foo instantiated with new"

---

使用 new.target

class A {
  constructor() {
    console.log(new.target.name);
  }
}

class B extends A { constructor() { super(); } }

var a = new A(); // logs "A"
var b = new B(); // logs "B"

没有

class A {
  constructor() {
    // class forces constructor to be called with `new`, so
    // `this` will always be set
    console.log(this.constructor.name);
  }
}

class B extends A { constructor() { super(); } }

var a = new A(); // logs "A"
var b = new B(); // logs "B"

希望对您有所帮助