Question

我需要一些javascript帮助。我正在使用一个简单的js文件用于一个小小的在线商店。演示页面的网址为：http://www.k-prim.biz/Esther/Store/proba.html 我正在使用的javascript称为orderform04.js。有一个错误：当输入产品1的q-ty 3时 - 价格为4.8，结果是14.399999999999999而不是14.4！

有人可以帮忙解决这个问题吗？

javascript也在这里：

function OrderForm(prefix, precision, firstChoice) {

this.prefix = prefix ? prefix : '';

// ****************************
// Configure here
// ****************************
// names - Set these according to how the html ids are set
this.FORM_NAME = this.prefix + 'frmOrder';
this.BTN_TOTAL = this.prefix + 'btnTotal';
this.TXT_OUT = this.prefix + 'txtTotal';

// partial names - Set these according to how the html ids are set
this.CHK = this.prefix + 'chk';
this.SEL = this.prefix + 'sel';
this.PRICE = this.prefix + 'txtPrice';

// precision for the decimal places
// If not set, then no decimal adjustment is made
this.precision = precision ? precision : -1;

// if the drop down has the first choice after index 1
// this is used when checking or unchecking a checkbox
this.firstChoice = firstChoice ? firstChoice : 1;
// ****************************

// form
this.frm = document.getElementById(this.FORM_NAME);

// checkboxes
this.chkReg = new RegExp(this.CHK + '([0-9]+)');
this.getCheck = function(chkId) {
    return document.getElementById(this.CHK + chkId);
};

// selects
this.selReg = new RegExp(this.SEL + '([0-9]+)');
this.getSelect = function(selId) {
    return document.getElementById(this.SEL + selId);
};

// price spans
this.priceReg = new RegExp(this.PRICE + '([0-9]+)');

// text output
this.txtOut = document.getElementById(this.TXT_OUT);

// button
this.btnTotal = document.getElementById(this.BTN_TOTAL);

// price array
this.prices = new Array();

var o = this;
this.getCheckEvent = function() {
    return function() {
        o.checkRetotal(o, this);
    };
};

this.getSelectEvent = function() {
    return function() {
        o.totalCost(o);
    };
};

this.getBtnEvent = function() {
    return function() {
        o.totalCost(o);
    };
};

/*
 * Calculate the cost
 * 
 * Required:
 *  Span tags around the prices with IDs formatted
 *  so each item's numbers correspond its select elements and input checkboxes.
 */
this.totalCost = function(orderObj) {
    var spanObj = orderObj.frm.getElementsByTagName('span');
    var total = 0.0;
    for (var i=0; i<spanObj.length; i++) {
        var regResult = orderObj.priceReg.exec(spanObj[i].id);
        if (regResult) {
            var itemNum = regResult[1];
            var chkObj = orderObj.getCheck(itemNum);
            var selObj = orderObj.getSelect(itemNum);
            var price = orderObj.prices[itemNum];
            var quantity = 0;
            if (selObj) {
                quantity = parseFloat(selObj.options[selObj.selectedIndex].text);
                quantity = isNaN(quantity) ? 0 : quantity;
                if (chkObj) chkObj.checked = quantity;
            } else if (chkObj) {
                quantity = chkObj.checked ? 1 : 0;
            }
            total += quantity * price;
        }
    }
    if (this.precision == -1) {
        orderObj.txtOut.value = total
    } else {
        orderObj.txtOut.value = total.toFixed(this.precision);
    }
};

/*
 * Handle clicks on the checkboxes
 *
 * Required:
 *  The corresponding select elements and input checkboxes need to be numbered the same
 *
 */
this.checkRetotal = function(orderObj, obj) {
    var regResult = orderObj.chkReg.exec(obj.id);
    if (regResult) {
        var optObj = orderObj.getSelect(regResult[1]);
        if (optObj) {
            if (obj.checked) {
                optObj.selectedIndex = orderObj.firstChoice;
            } else {
                optObj.selectedIndex = 0;
            }
        }
        orderObj.totalCost(orderObj);
    }
};

/*
 * Set up events
 */
this.setEvents = function(orderObj) {
    var spanObj = orderObj.frm.getElementsByTagName('span');
    for (var i=0; i<spanObj.length; i++) {
        var regResult = orderObj.priceReg.exec(spanObj[i].id);
        if (regResult) {
            var itemNum = regResult[1];
            var chkObj = orderObj.getCheck(itemNum);
            var selObj = orderObj.getSelect(itemNum);
            if (chkObj) {
                chkObj.onclick = orderObj.getCheckEvent();
            }
            if (selObj) {
                selObj.onchange = orderObj.getSelectEvent();
            }
            if (orderObj.btnTotal) {
                orderObj.btnTotal.onclick = orderObj.getBtnEvent();
            }
        }
    }
};
this.setEvents(this);

/*
 *
 * Grab the prices from the html
 * Required:
 *  Prices should be wrapped in span tags, numbers only.
 */
this.grabPrices = function(orderObj) {
    var spanObj = orderObj.frm.getElementsByTagName('span');
    for (var i=0; i<spanObj.length; i++) {
        if (orderObj.priceReg.test(spanObj[i].id)) {
            var regResult = orderObj.priceReg.exec(spanObj[i].id);
            if (regResult) {
                orderObj.prices[regResult[1]] = parseFloat(spanObj[i].innerHTML);
            }
        }
    }
};
this.grabPrices(this);

}

Answer 1

看看Floating Point Guide - 这只是计算机代表十进制数字的原因，而不是程序本身的错误。

解决方案是使用某种十进制数据类型而不是浮点数据类型。 Javascript本身似乎没有一个;请参阅https://stackoverflow.com/questions/744099/javascript-bigdecimal-library进行讨论并提出一些建议的解决方法。

指南的Javascript-specific page上有一个链接，指向可以解决问题的Javascript BigDecimal库。

Answer 2

解决此问题的复杂且技术上正确的方法是使用某种不在内部使用浮点数的十进制库，但使用其他人建议的所有整数。

根据您使用的数字，您有时可以通过使用浮点数并将所有内容四舍五入到两位数来完成所有操作。例如，在您的情况下：

14.399999999999999.toFixed（2）= 14.40这就是你想要的。

需要帮助Javascript

2 个答案: