@rbxts/jsnatives

Object.is

Determines whether two values are the same value.

Signature

function is<T, U>(obj: T, other: U): obj is T & U

Description

The Object.is() method determines whether two values are the same value. It performs a reference check rather than a content equality check.

Unlike the equality operators (== and ===), Object.is() treats NaN as equal to itself and treats -0 and +0 as different.

The method returns a type predicate that narrows the type to T & U when the objects are the same.

Examples

Basic reference check

const objA = {};
const objB = {};

print(Object.is(objA, objB)); // false (different objects)

Same reference

const objA = {};
const objB = objA;

print(Object.is(objA, objB)); // true (same reference)

Nested references

const objA = {};
const objB = {ref: objA};

print(Object.is(objA, objB.ref)); // true (same reference)

With primitive values

print(Object.is(1, 1)); // true
print(Object.is("hello", "hello")); // true
print(Object.is(true, true)); // true
print(Object.is(null, null)); // true
print(Object.is(undefined, undefined)); // true

print(Object.is(NaN, NaN)); // true (unlike ===)
print(Object.is(0, -0)); // false (unlike ===)

Type narrowing with is

function processValues<T, U>(value1: T, value2: U) {
  if (Object.is(value1, value2)) {
    // In this block, value1 and value2 are typed as T & U
    return "Values are the same";
  } else {
    // In this block, value1 is T and value2 is U
    return "Values are different";
  }
}