js浮點數的加減乘除

;(function(root, factory) {

    // Support AMD
    if (typeof define === 'function' && define.amd) {
        define([], factory);

        // Support CommonJS
    } else if (typeof exports === 'object') {
        var accFloating = factory();

        // Support NodeJS & Component, which allow module.exports to be a function
        if (typeof module === 'object' && module && module.exports) {
            exports = module.exports = accFloating;
        }

        // Support CommonJS 1.1.1 spec
        exports.accFloating = accFloating;

        // Support vanilla script loading
    } else {
        root.accFloating = factory();
    }

}(this, function() {
    /**
     * 獲取小數點後數字長度
     * @author zhongjiewang
     * @param  {Number} num 數字
     * @return {Number}     長度
     */
    function decimalLength(num) {
        var str = num.toString();
        var index = str.indexOf('.');
        return index == -1 ? 0 : str.substr(index + 1).length;
    }

    /**
     * 小數點後補齊0做爲整數
     * @author zhongjiewang
     * @param  {Number} num    數字
     * @param  {Number} length 補齊的長度
     * @return {Number}        整數
     */
    function suffixInteger(num, length) {
        var str = num.toString();
        var decimalLen = decimalLength(num);
        str += Math.pow(10, length - decimalLen).toString().substr(1);
        return Number(str.replace('.', ''));
    }

    // 加法
    function accAdd(num1, num2) {
        var r1 = decimalLength(num1);
        var r2 = decimalLength(num2);

        var max = Math.max(r1, r2);

        var n1 = suffixInteger(num1, max);
        var n2 = suffixInteger(num2, max);

        return Number(((n1 + n2) / Math.pow(10, max)).toFixed(max));
    }

    // 減法
    function accSubtr(num1, num2) {
        var r1 = decimalLength(num1);
        var r2 = decimalLength(num2);

        var max = Math.max(r1, r2);

        var n1 = suffixInteger(num1, max);
        var n2 = suffixInteger(num2, max);

        return Number(((n1 - n2) / Math.pow(10, max)).toFixed(max));
    }
    // 乘法
    function accMul(num1, num2) {
        var r1 = decimalLength(num1);
        var r2 = decimalLength(num2);

        var max = Math.max(r1, r2);

        var n1 = suffixInteger(num1, max);
        var n2 = suffixInteger(num2, max);

        return n1 * n2 / Math.pow(10, max * 2);

    }
    // 除法
    function accDiv(num1, num2) {
        var r1 = decimalLength(num1);
        var r2 = decimalLength(num2);

        var max = Math.max(r1, r2);

        var n1 = suffixInteger(num1, max);
        var n2 = suffixInteger(num2, max);

        return n1 / n2;
    }

    return {
        add: accAdd,
        subtr: accSubtr,
        mul: accMul,
        div: accDiv
    }

}));