implementation Object.is (js)

implementation Object.is (js).js

if (!Object.is || true) {
	Object.is = function ObjectIs(x,y) {
		var xNegZero = isItNegZero(x);
		var yNegZero = isItNegZero(y);

    /* 先過濾 -0 */
		if (xNegZero || yNegZero) {
			return xNegZero && yNegZero;
    }
    /* 再過濾 NaN */
		else if (isItNaN(x) && isItNaN(y)) {
			return true;
    }
    /* 排除 corner case 再回來用嚴格相等(===)  */
		else if (x === y) {
			return true;
		}

		return false;

		// **********

    /** 
     * @description -0 
     * @condition value === 0
     * @condition 1 / num : 利用可以區分正負的特性，嚴格等於對 NegZero (===) 無效 
     * 1/0 = (+)Infinity , 1/-0 = -Infinity 
     */
		function isItNegZero(num) {
			return num === 0 && (1 / num) === -Infinity;
		}

    /**
     * @description 有人會先判斷是不是數字，在判斷是不是 isNaN 
     * @example 這邊直接用 IEEE 754 定義 (NaN ≠ x) = false，一樣可以簡易判斷，全 js 只有 NaN 這個特殊值符合條件
     * */
		function isItNaN(self) {
			return self !== self;
		}
	};
}




// tests: 以下都要為 true
console.log(Object.is(42,42) === true);
console.log(Object.is("foo","foo") === true);
console.log(Object.is(false,false) === true);
console.log(Object.is(null,null) === true);
console.log(Object.is(undefined,undefined) === true);
console.log(Object.is(NaN,NaN) === true);
console.log(Object.is(-0,-0) === true);
console.log(Object.is(0,0) === true);

console.log(Object.is(-0,0) === false);
console.log(Object.is(0,-0) === false);
console.log(Object.is(0,NaN) === false);
console.log(Object.is(NaN,0) === false);
console.log(Object.is(42,"42") === false);
console.log(Object.is("42",42) === false);
console.log(Object.is("foo","bar") === false);
console.log(Object.is(false,true) === false);
console.log(Object.is(null,undefined) === false);
console.log(Object.is(undefined,null) === false);