MUI中小数点的数字输入框，步进step为小数时的需求和浮点数的精确问题

项目需要能步进小数点的数字输入框，但是mui 的数字输入框只能步进整数，发现只要把 源码中的parseInt 改成 parseFloat 就行了，可是后来新的问题又出现了,

浮点数进行加减的精确问题，这是所有编程语言都有的.

下面是完美解决方案，只需将mui.js中关于数字输入框的源代码改成如下即可，mui.js中的位置大概在8158行左右

/**
 * 数字输入框
 * varstion 1.0.1
 * by Houfeng
 * Houfeng@DCloud.io
 */
 
(function($) {
 
    var touchSupport = ('ontouchstart' in document);
    var tapEventName = touchSupport ? 'tap' : 'click';
    var changeEventName = 'change';
    var holderClassName = 'mui-numbox';
    var plusClassSelector = '.mui-btn-numbox-plus,.mui-numbox-btn-plus';
    var minusClassSelector = '.mui-btn-numbox-minus,.mui-numbox-btn-minus';
    var inputClassSelector = '.mui-input-numbox,.mui-numbox-input';
 
    
    this.floatAdd=function(arg1, arg2){
             var r1, r2, m, c;
            try {
                r1 = arg1.toString().split(".")[1].length;
            }
            catch (e) {
                r1 = 0;
            }
            try {
                r2 = arg2.toString().split(".")[1].length;
            }
            catch (e) {
                r2 = 0;
            }
            c = Math.abs(r1 - r2);
            m = Math.pow(10, Math.max(r1, r2));
            if (c > 0) {
                var cm = Math.pow(10, c);
                if (r1 > r2) {
                    arg1 = Number(arg1.toString().replace(".", ""));
                    arg2 = Number(arg2.toString().replace(".", "")) * cm;
                } else {
                    arg1 = Number(arg1.toString().replace(".", "")) * cm;
                    arg2 = Number(arg2.toString().replace(".", ""));
                }
            } else {
                arg1 = Number(arg1.toString().replace(".", ""));
                arg2 = Number(arg2.toString().replace(".", ""));
            }
            return (arg1 + arg2) / m;
        },
        this.floatSub=function(arg1,arg2){
            var r1, r2, m, n;
            try {
                r1 = arg1.toString().split(".")[1].length;
            }
            catch (e) {
                r1 = 0;
            }
            try {
                r2 = arg2.toString().split(".")[1].length;
            }
            catch (e) {
                r2 = 0;
            }
            m = Math.pow(10, Math.max(r1, r2)); //last modify by deeka //动态控制精度长度
            n = (r1 >= r2) ? r1 : r2;
            return ((arg1 * m - arg2 * m) / m).toFixed(n);
        }
 
    var _this=this;
    var Numbox = $.Numbox = $.Class.extend({
        /**
         * 构造函数
         **/
        init: function(holder, options) {
            var self = this;
            if (!holder) {
                throw "构造 numbox 时缺少容器元素";
            }
            self.holder = holder;
            options = options || {};
            options.step = parseFloat(options.step || 1);
            self.options = options;
            self.input = $.qsa(inputClassSelector, self.holder)[0];
            self.plus = $.qsa(plusClassSelector, self.holder)[0];
            self.minus = $.qsa(minusClassSelector, self.holder)[0];
            self.checkValue();
            self.initEvent();
        },
        /**
         * 初始化事件绑定
         **/
        initEvent: function() {
            var self = this;
            self.plus.addEventListener(tapEventName, function(event) {
//              var val = parseFloat(self.input.value) + self.options.step;
                var val=_this.floatAdd(parseFloat(self.input.value),self.options.step);
                self.input.value = val.toString();
                $.trigger(self.input, changeEventName, null);
            });
            self.minus.addEventListener(tapEventName, function(event) {
//              var val = parseFloat(self.input.value) - self.options.step;
                var val=_this.floatSub(parseFloat(self.input.value),self.options.step);
                self.input.value = val.toString();
                $.trigger(self.input, changeEventName, null);
            });
            self.input.addEventListener(changeEventName, function(event) {
                self.checkValue();
                var val = parseFloat(self.input.value);
                //触发顶层容器
                $.trigger(self.holder, changeEventName, {
                    value: val
                });
            });
        },
        /**
         * 获取当前值
         **/
        getValue: function() {
            var self = this;
            return parseFloat(self.input.value);
        },
        /**
         * 验证当前值是法合法
         **/
        checkValue: function() {
            var self = this;
            var val = self.input.value;
            if (val == null || val == '' || isNaN(val)) {
                self.input.value = self.options.min || 0;
                self.minus.disabled = self.options.min != null;
            } else {
                var val = parseFloat(val);
                if (self.options.max != null && !isNaN(self.options.max) && val >= parseFloat(self.options.max)) {
                    val = self.options.max;
                    self.plus.disabled = true;
                } else {
                    self.plus.disabled = false;
                }
                if (self.options.min != null && !isNaN(self.options.min) && val <= parseFloat(self.options.min)) {
                    val = self.options.min;
                    self.minus.disabled = true;
                } else {
                    self.minus.disabled = false;
                }
                self.input.value = val;
            }
        },
        /**
         * 更新选项
         **/
        setOption: function(name, value) {
            var self = this;
            self.options[name] = value;
        },
        /**
         * 动态设置新值
         **/
        setValue: function(value) {
            this.input.value = value;
            this.checkValue();
        }
        
    });
 
    $.fn.numbox = function(options) {
        var instanceArray = [];
        //遍历选择的元素
        this.each(function(i, element) {
            if (element.numbox) {
                return;
            }
            if (options) {
                element.numbox = new Numbox(element, options);
            } else {
                var optionsText = element.getAttribute('data-numbox-options');
                var options = optionsText ? JSON.parse(optionsText) : {};
                options.step = element.getAttribute('data-numbox-step') || options.step;
                options.min = element.getAttribute('data-numbox-min') || options.min;
                options.max = element.getAttribute('data-numbox-max') || options.max;
                element.numbox = new Numbox(element, options);
            }
        });
        return this[0] ? this[0].numbox : null;
    }
 
    //自动处理 class='mui-locker' 的 dom
    $.ready(function() {
        $('.' + holderClassName).numbox();
    });
 
}(mui));