🔸new.target

JS ⟩ value ⟩ object ⟩ create ⟩ new ⟩ new.target

a function can know whether it is invoked with new by checking new.target. new.target is only undefined when the function is invoked without new.

in normal function calls, new.target is undefined.

function User(name) {
    // ⭐️ if called normally, add `new`.
    if (!new.target) { return new User(name); }
    this.name = name;
}

let joe = User('Joe');    // ⭐️ `new` not required now

in class constructors (or function called using new), new.target refers to the constructor/function that was directly invoked by new. for example:

new A(); // new.target === A
new B(); // new.target === B

⚠️ class constructors cannot be invoked without 'new'.

new.target "pseudo-property" is available in all functions.

💾 replit：new.target

// ----------------------------------------------------
// in class constructors, `new.target` refers to 
// the constructor that was directly invoked by `new`.
// for example:
//     new A();     // new.target === A
//     new B();     // new.target === B
// ----------------------------------------------------
class A {
    constructor() {
        console.log(`new ${new.target.name}(): new.target === A ? ${new.target === A}`);
    }
}

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

const a = new A();         // new.target === A ? true
const b = new B();         // new.target === A ? false

// A();
// ⛔️ TypeError: Class constructor `A` cannot be invoked without 'new'

// ----------------------------------------------------
// in normal function calls, `new.target` is `undefined`.
// ----------------------------------------------------
function User(name) {
    // ⭐ if called without `new`, add `new` automatically.
    if (!new.target) { return new User(name) }
    this.name = name;
}

let joe = User('Joe');    // ⭐ `new` not required now
console.log(joe.name);    // 'Joe'

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Last updated 3 years ago

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