How do you polyfill Javascript ES6 `new.target`?

Question

Some ES6 features are really easy to polyfill:

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

How would you polyfill new.target? It triggers a syntax error when it's used in an unsupported browser. try/catch doesn't work because it's a syntax error. I don't have to use new.target, I'm mostly just curious.

Answer 1

As Jaromanda commented, you cannot polyfill new syntax, but you can easily work around some new.target use cases for now

Taking a look at the new.target docs you'll see some examples that can easily be written with es5

with 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"

without

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"

---

with 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"

without

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"

Hope this helps a little