es.function.has-instance.js

'use strict';
var isObject = require('../internals/is-object');
var definePropertyModule = require('../internals/object-define-property');
var getPrototypeOf = require('../internals/object-get-prototype-of');
var wellKnownSymbol = require('../internals/well-known-symbol');

var HAS_INSTANCE = wellKnownSymbol('hasInstance');
var FunctionPrototype = Function.prototype;

// `Function.prototype[@@hasInstance]` method
// https://tc39.github.io/ecma262/#sec-function.prototype-@@hasinstance
if (!(HAS_INSTANCE in FunctionPrototype)) {
  definePropertyModule.f(FunctionPrototype, HAS_INSTANCE, { value: function (O) {
    if (typeof this != 'function' || !isObject(O)) return false;
    if (!isObject(this.prototype)) return O instanceof this;
    // for environment w/o native `@@hasInstance` logic enough `instanceof`, but add this:
    while (O = getPrototypeOf(O)) if (this.prototype === O) return true;
    return false;
  } });
}