ES6對數值對象Number進行了擴展,

// ES實現Number.isFinite()
(function (global) {var global_isFinite = global.isFinite;Object.defineProperty(Number, 'isFinite', {value: function isFinite(value) {return typeof value === 'number' && 'global_isFinite(value);},configurable: true,enumberable: false,writable: true});
}) (this);

// ES5實現Number.isNaN()
(function (global) {var global_isNaN = global.isNaN;Object.defineProperty(Number, 'isNaN', {value: function isNaN(value) {return typeof value === 'number' && global_isNaN(value);},configurable: true,enumerable: false,writable: true});
}) (this);

// ES5實現Number.isInterger()
(function (global) {var floor = Math.floor,isFinite = global.isFinite;Object.definePropery(Number, 'isInteger', {value: function isInteger(value) {return typeof value === 'number' &&isFinite(value) &&floor(value) === value;},configurable: true,enumerable: false,writable: true});
}) (this)

// ES5實現Number.isSafeInteger
var MIN_SAFE_INTEGER = -Math.pow(2, 53);
var MAX_SAFE_INTEGER = Math.pow(2, 53);
Number.isSafeInteger = function (n) {return (typeof n === 'number' &&Math.round(n) === n &&Number.MIN_SAFE_INTEGER <= n &&n <= Number.MAX_SAFE_INTEGER);
}

// Math.trunc: 除去一個數的小數部分
Math.trunc = Math.trunc || function (x) {return x < 0 ? Math.ceil(x) : Math.floor(x);
};

// Math.sign:判斷一個數是正數、負數,還是零,或非數字
Math.sign = Math.sign || function (x) {x = +x;    // 轉換成一個數if (x === 0 || isNaN(x)) {return x;}return x > 0 ? 1: -1;
};

// Math.cbrt: 計算一個數的立方根
Math.cbrt = Math.cbrt || function (x) {var y = Math.pow(Math.abs(x), 1/3);return x < 0 ? -y : y;
};

參考 《ES6 標準入門》P86~P96