===

. . , . . , NaN , +0 -0 .

const num = 0;
const obj = new String("0");
const str = "0";

console.log(num === num); // true
console.log(obj === obj); // true
console.log(str === str); // true

console.log(num === obj); // false
console.log(num === str); // false
console.log(obj === str); // false
console.log(null === undefined); // false
console.log(obj === null); // false
console.log(obj === undefined); // false

. " " . . 0 . , +0 -0 . NaN (: ) . NaN . ((x !== x) true x NaN .)

=== Array.prototype.indexOf(), Array.prototype.lastIndexOf(), TypedArray.prototype.indexOf(), TypedArray.prototype.lastIndexOf(), case . , indexOf(NaN) NaN NaN switch case .

console.log([NaN].indexOf(NaN)); // -1
switch (NaN) {
  case NaN:
    console.log("Surprise"); //   .
}

==

. , A == B A B B == A ( ). == .

1. .
   • : true .
   • : true .
   • : true . +0 -0 . NaN false . NaN NaN .
   • : true false true .
   • BigInt: true .
   • Symbol: symbol true .
2. null undefined true null undefined . false .
3. .
4. (, , , Symbol, BigInt ) . .
   • , 1 .
   • Symbol , false .
   • , . true 1 false 0 . .
   • : . NaN false .
   • BigInt: . Infinity NaN false .
   • BigInt: BigInt() BigInt . false .

, ECMAScript undefined null . ( document.all ) undefined . . null == A undefined == A A undefined true . undefined null .

. , .

0, bigint 0n, '0', toString() '0' .

const num = 0;
const big = 0n;
const str = "0";
const obj = new String("0");

console.log(num == str); // true
console.log(big == num); // true
console.log(str == big); // true

console.log(num == obj); // true
console.log(big == obj); // true
console.log(str == obj); // true

== .

Object.is()

. ( Liskov .) .

//    NEGATIVE_ZERO  Number  .
Object.defineProperty(Number, "NEGATIVE_ZERO", {
  value: -0,
  writable: false,
  configurable: false,
  enumerable: false,
});

function attemptMutation(v) {
  Object.defineProperty(Number, "NEGATIVE_ZERO", { value: v });
}

Object.defineProperty , . v -0 , . , .

Object.is . ID .

, +0 -0 .

JavaScript API , .

function sameValueZero(x, y) {
  if (typeof x === "number" && typeof y === "number") {
    // x y (-0 0  )   NaN.
    return x === y || (x !== x && y !== y);
  }
  return x === y;
}

NaN , -0 0 . NaN , . Array.prototype.includes(), TypedArray.prototype.includes(), Map Set .

"" . , . (: 6 == "6"). . .

" " , " " 1 "" . Object.is , "" , "" (, ). Object.is NaN . Object.is(NaN, NaN) false Object.is -0 +0 / . NaN . Object.is .

Object.is() ?

0 Object.is , Object.defineProperty . , Object.is === . NaN true , NaN ( ECMAScript isNaN ) 0 .

-0 +0 .

- ( )

.

js

const stoppingForce = obj.mass * -obj.velocity;

obj.velocity 0( 0 ) -0 stopsingForce .

Math.atan2, Math.ceil, Math.pow, Math.round

-0 -0 . Math.pow -Infinity -0 . .

Math.floor, Math.max, Math.min, Math.sin, Math.sqrt, Math.tan

-0 -0 . Math.min(-0, +0) -0 . , .

~, <<, >>

ToInt32 . 32 0 -0 . , Object.is(~~(-0), -0) Object.is(-0 << 2 >> 2, -0) false .

0 Object.is . -0 +0 .

: Object.is() NaN

Object.is NaN . NaN .

const f2b = (x) => new Uint8Array(new Float64Array([x]).buffer);
const b2f = (x) => new Float64Array(x.buffer)[0];
// NaN   .
const n = f2b(NaN);
// NaN        .
n[0] = 1;
const nan2 = b2f(n);
console.log(nan2); // NaN
console.log(Object.is(nan2, NaN)); // true
console.log(f2b(NaN)); // Uint8Array(8) [0, 0, 0, 0, 0, 0, 248, 127]
console.log(f2b(nan2)); // Uint8Array(8) [1, 0, 0, 0, 0, 0, 248, 127]

• JS