JS: Function.prototype[Symbol.hasInstance]

New in JS2015.

f[Symbol.hasInstance](obj)

Return true if the value of f.prototype is in the Prototype Chain of obj. Else, false.

[see Symbol Tutorial]

The following are equivalent:

• f[Symbol.hasInstance](obj)
• obj instanceof f
• f.prototype.isPrototypeOf(obj)

[see instanceof Operator]

// Example Symbol.hasInstance on a buildin function

const xx = [3, 4];

console.log(Array[Symbol.hasInstance](xx));
console.log(xx instanceof Array);
console.log(Array.prototype.isPrototypeOf(xx));

// Example Symbol.hasInstance on a user-defined function

function F() {}

let xx = new F();

console.log(F[Symbol.hasInstance](xx));
console.log(xx instanceof F);
console.log(F.prototype.isPrototypeOf(xx));