Array.prototype.valueOf() returns the same array object (this). It does not copy elements or build a string. Inherited from Object.prototype (ES3)—rarely needed in day-to-day code.
array.valueOf() → the same array (same reference)
arr === arr.valueOf() → true
valueOf() → object (the array)
toString() → "a,b,c" string
shared reference → mutations affect the original
not for deep equality of two arraysCall array.valueOf. Start with this line.
array.valueOf()| Call | What it does |
|---|---|
array.valueOf() | Primary signature. |
array.valueOf(...) | Call with the arguments your case needs. |
Built into JavaScript. Call valueOf(...) on an array instance — no import required.
array.valueOf()| Parameter | Description |
|---|---|
| Receiver array | Required. Object whose reference is returned |
| Return Value | Description |
|---|---|
| * | The same array (this) |
Prove valueOf() returns the identical object—not a clone.
const numbers = [1, 2, 3, 4, 5];
const result = numbers.valueOf();
console.log(result);
console.log(numbers === result); // truenumbers points to one object.result.Changing the return value changes the original array.
const items = ["a", "b"];
const ref = items.valueOf();
ref.push("c");
console.log(items); // ["a", "b", "c"]ref is another name for items.push("c") grows that one object.items shows the new element too.slice() or [...items], not valueOf().valueOf() vs toString()Different jobs: object reference vs comma-separated string.
const nums = [10, 20, 30];
console.log(typeof nums.valueOf()); // "object"
console.log(typeof nums.toString()); // "string"
console.log(nums.toString()); // "10,20,30"typeof reports "object" (arrays are objects)."" + nums ends up like toString().toString/join; need the array → just use nums.Array.prototype.valueOf() has been part of JavaScript since ES3. It is available in every browser and Node.js environment you are likely to meet.
Supported in all modern browsers, Internet Explorer, and every Node.js version. No polyfill required.
Bottom line: Safe everywhere. This is one of the oldest array/object methods in the language.
Return a new array with one index replaced—without mutating the original.
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