JavaScript: Triple Equal Operator

Compare Primitives

Triple Equal can compare most Primitive Values such as string, number, Symbol, undefined, null, except NaN.

console.log("x" === "x");
console.log(3 === 3);
console.log(3 === 3.0);
console.log(Infinity === Infinity);

NaN cannot be compared with triple equal.

console.log((NaN === NaN) === false);

use:

• Object.is
• Number.isNaN

Test Object Equality by Triple Equal

Objects (including Array) cannot be compared with triple equal.

When a object is assigned to a variable, the variable holds a reference to the object.

If 2 variables hold the same reference, they are equal.

const x = { "a": 3 };
const y = x; // x and y holds the same reference
console.log(x === y);

but 2 objects with same property values, are still considered different if they have different reference.

// Objects cannot be compared with triple equal

console.log(([] === []) === false);
console.log(({} === {}) === false);
console.log(({ "a": 3 } === { "a": 3 }) === false);

to test equality of objects, see JavaScript: Test Object Equality 🚀

No Auto Type Convert Conversion

Triple equale does not convert Value Types implicitly.

console.log(([] === "") === false);
console.log(("" === {}) === false);
console.log(("0" === 0) === false);
console.log(("" === 0) === false);
console.log((1 === true) === false);