JS: Object.prototype.valueOf

Object.prototype.valueOf

returns this Binding it receives.

e.g. myObj.valueOf() === myObj

If Type of this Binding is not a object type, either return a error, or convert it to a object type, return it.

It has similar behavior as the Object Constructor Object(arg), except in the Object(arg) case, if arg is null or undefined, it creates a empty object, while in the valueOf() case, it throws TypeError.

It's usually called in one of the following form:

• Object.prototype.valueOf.call(x)
• Reflect.apply(Object.prototype.valueOf, x, [])

[see Function Call, Apply, Bind]

Here is a table showing the conversion:

Value	Result
undefined	throw TypeError
null	throw TypeError
true or false	boolean object
number	number object
string	string object
symbol	symbol object
object	object

const jj = {};
console.log(jj.valueOf() === jj);

// testing use of  Object.prototype.valueOf
// but with a primitive value as argument

const x1 = Reflect.apply(Object.prototype.valueOf, true, []);
console.log(typeof x1 === "object");
console.log(Boolean(x1) === true);

const x2 = Reflect.apply(Object.prototype.valueOf, 3, []);
console.log(typeof x2 === "object");
console.log(Number(x2) === 3);

const x3 = Reflect.apply(Object.prototype.valueOf, "abc", []);
console.log(typeof x3 === "object");
console.log(String(x3) === "abc");

// Error example
// console.log(Object.prototype.valueOf.call(null));
// TypeError: Cannot convert undefined or null to object