簡單四則運(yùn)算及表達(dá)式校驗(yàn)和轉(zhuǎn)換工具類，僅供參考。
完整工具類請往我的github項(xiàng)目bee.js

//簡單四則運(yùn)算
ElementaryArithmeticUtils = {
        //運(yùn)算符優(yōu)先級
        operatorPrecedence: {
            "+": 0,
            "-": 0,
            "*": 1,
            "×": 1,
            "÷": 1,
            "/": 1
        },
        //運(yùn)算符
        operator: {
            "+": "+",
            "-": "-",
            "*": "*",
            "×": "*",
            "÷": "/",
            "/": "/"
        },
        //加法
        add: function(operandLeft, operandRight) {
            var operand1 = operandLeft.toString();
            var operand2 = operandRight.toString();
            var decimalPlace1 = operand1.indexOf(".") >= 0 ? operand1.split(".")[1].length : 0;
            var decimalPlace2 = operand2.indexOf(".") >= 0 ? operand2.split(".")[1].length : 0;
            var multiple = Math.pow(10, Math.max(decimalPlace1, decimalPlace2));
            return(operandLeft * multiple + operandRight * multiple) / multiple;
        },
        //減法
        subtract: function(operandLeft, operandRight) {
            var operand1 = operandLeft.toString();
            var operand2 = operandRight.toString();
            var decimalPlace1 = operand1.indexOf(".") >= 0 ? operand1.split(".")[1].length : 0;
            var decimalPlace2 = operand2.indexOf(".") >= 0 ? operand2.split(".")[1].length : 0;
            var multiple = Math.pow(10, Math.max(decimalPlace1, decimalPlace2));
            //toFixed避免多出來小數(shù)位，如 11.3-10.12000=1.1800000000000015
            var decimalPlace = (decimalPlace1 >= decimalPlace2) ? decimalPlace1 : decimalPlace2;
            return((operandLeft * multiple - operandRight * multiple) / multiple).toFixed(decimalPlace);
        },
        //乘法
        multiply: function(operandLeft, operandRight) {
            var operand1 = operandLeft.toString();
            var operand2 = operandRight.toString();
            var decimalPlace1 = operand1.indexOf(".") >= 0 ? operand1.split(".")[1].length : 0;
            var decimalPlace2 = operand2.indexOf(".") >= 0 ? operand2.split(".")[1].length : 0;
            var multiple1 = Math.pow(10, decimalPlace1);
            var multiple2 = Math.pow(10, decimalPlace2);
            return((operandLeft * multiple1) * (operandRight * multiple2)) / Math.pow(10, decimalPlace1 + decimalPlace2);
        },
        //除法
        divide: function(operandLeft, operandRight) {
            var operand1 = operandLeft.toString();
            var operand2 = operandRight.toString();
            var decimalPlace1 = operand1.indexOf(".") >= 0 ? operand1.split(".")[1].length : 0;
            var decimalPlace2 = operand2.indexOf(".") >= 0 ? operand2.split(".")[1].length : 0;
            var multiple1 = Math.pow(10, decimalPlace1);
            var multiple2 = Math.pow(10, decimalPlace2);
            return((operandLeft * multiple1) / (operandRight * multiple2)) * Math.pow(10, decimalPlace2 - decimalPlace1);
        },
        //校驗(yàn)表達(dá)式的合法性
        isArithmeticExpression: function(expression) {
            try {
                expression = expression.replace(/÷/g, "/").replace(/×/g, "*");
                var result = eval(expression);
            } catch(e) {
                return false;
            }
            return true;
        },
        //計算
        calculate: function(expression) {
            var value = eval(expression);
            return value;
        },
        //中綴表達(dá)式轉(zhuǎn)后綴表達(dá)式
        infixToPostfixExpression: function(expression) {
            expression = Bee.StringUtils.deleteWhitespace(expression);
            expression = this.eliminatePositiveOrNegativeSign(expression);
            var operatorStack = [];
            var resultStack = [];
            var elementArr = expression.match(/[-+/÷*×()]|(?:[1-9]d*|0)(?:.d+)?/g);
            var size = elementArr.length;
            for(var i = 0; i < size; i++) {
                if(Bee.StringUtils.isNumeric(elementArr[i])) {
                    //如果是數(shù)值
                    resultStack.push(elementArr[i]);
                } else {
                    //操作符棧頂元素
                    var operatorStackTopElement = operatorStack.length === 0 ? "" : operatorStack[operatorStack.length - 1];
                    //運(yùn)算符
                    if(operatorStack.length === 0 || elementArr[i] === "(" || operatorStackTopElement === "(" || this.operatorPrecedence[elementArr[i]] > this.operatorPrecedence[operatorStackTopElement]) {
                        //操作符棧為空或棧頂元素為右括號")"，或操作符的優(yōu)先級比棧頂運(yùn)算符高或相等，直接入棧
                        operatorStack.push(elementArr[i]);
                    } else {
                        //如果是右括號")"，則依次彈出操作符棧頂?shù)倪\(yùn)算符，并壓入結(jié)果棧，直到遇到左括號"("為止，左右括號不壓入結(jié)果棧；
                        if(elementArr[i] === ")") {
                            for(var index = operatorStack.length - 1; index >= 0; index--) {
                                if(operatorStack[index] === "(") {
                                    operatorStack.pop();
                                    break;
                                } else {
                                    resultStack.push(operatorStack.pop());
                                }
                            }
                        } else {
                            //將符號棧頂?shù)倪\(yùn)算符彈出并壓入到結(jié)果棧中，再次與符號棧中新的棧頂運(yùn)算符相比較
                            resultStack.push(operatorStack.pop());
                            i--;
                            continue;
                        }
                    }
                }
            }
            //處理操作符棧剩余的符號        
            if(operatorStack.length > 0) {
                for(var j = operatorStack.length - 1; j >= 0; j--) {
                    resultStack.push(operatorStack.pop());
                }
            }
            //結(jié)果返回
            return resultStack.join(" ");
        },
        //中綴表達(dá)式轉(zhuǎn)前綴表達(dá)式(結(jié)果以空格隔開)
        infixToPrefixExpression: function(expression) {
            expression = Bee.StringUtils.deleteWhitespace(expression);
            expression = this.eliminatePositiveOrNegativeSign(expression);
            var operatorStack = [];
            var resultStack = [];
            var elementArr = expression.match(/[-+/÷*×()]|(?:[1-9]d*|0)(?:.d+)?/g);
            var size = elementArr.length;
            for(var i = size - 1; i >= 0; i--) {
                if(Bee.StringUtils.isNumeric(elementArr[i])) {
                    //如果是數(shù)值
                    resultStack.push(elementArr[i]);
                } else {
                    //操作符棧頂元素
                    var operatorStackTopElement = operatorStack.length === 0 ? "" : operatorStack[operatorStack.length - 1];
                    //運(yùn)算符
                    if(operatorStack.length === 0 || elementArr[i] === ")" || operatorStackTopElement === ")" || this.operatorPrecedence[elementArr[i]] >= this.operatorPrecedence[operatorStackTopElement]) {
                        //操作符棧為空或棧頂元素為右括號")"，或操作符的優(yōu)先級比棧頂運(yùn)算符高或相等，直接入棧
                        operatorStack.push(elementArr[i]);
                    } else {
                        //如果是左括號"("，則依次彈出操作符棧頂?shù)倪\(yùn)算符，并壓入結(jié)果棧，直到遇到右括號")"為止，左右括號不壓入結(jié)果棧；
                        if(elementArr[i] === "(") {
                            for(var index = operatorStack.length - 1; index >= 0; index--) {
                                if(operatorStack[index] === ")") {
                                    operatorStack.pop();
                                    break;
                                } else {
                                    resultStack.push(operatorStack.pop());
                                }
                            }
                        } else {
                            //將符號棧頂?shù)倪\(yùn)算符彈出并壓入到結(jié)果棧中，再次與符號棧中新的棧頂運(yùn)算符相比較
                            resultStack.push(operatorStack.pop());
                            i++;
                            continue;
                        }

                    }
                }
            }
            //處理操作符棧剩余的符號        
            if(operatorStack.length > 0) {
                for(var j = operatorStack.length - 1; j >= 0; j--) {
                    resultStack.push(operatorStack.pop());
                }
            }
            //結(jié)果返回
            return resultStack.reverse().join(" ");
        },
        //解決正負(fù)號問題-1轉(zhuǎn)為0-1;+1轉(zhuǎn)為0+1
        eliminatePositiveOrNegativeSign: function(expression) {
            return expression.replace(/((|^)([-+])/g, "$10$2");
        },
        //把中綴表達(dá)式轉(zhuǎn)為前綴表達(dá)式，再計算
        calculateByPrefixExpression: function(expression) {
            var elementArr = this.infixToPrefixExpression(expression).split(" ");
            var size = elementArr.length;
            var resultStack = [];
            for(var i = size - 1; i >= 0; i--) {
                if(Bee.StringUtils.isNumeric(elementArr[i])) {
                    //如果是數(shù)值
                    resultStack.push(elementArr[i]);
                } else {
                    var operand1 = resultStack.pop();
                    var operand2 = resultStack.pop();
                    var result;
                    switch(elementArr[i]) {
                        case "+":
                            result = Bee.ElementaryArithmeticUtils.add(operand1, operand2);
                            break;
                        case "-":
                            result = Bee.ElementaryArithmeticUtils.subtract(operand1, operand2);
                            break;
                        case "×":
                        case "*":
                            result = Bee.ElementaryArithmeticUtils.multiply(operand1, operand2);
                            break;
                        case "/":
                        case "÷":
                            result = Bee.ElementaryArithmeticUtils.divide(operand1, operand2);
                            break;
                        default:
                            result = "";
                            alert("The operator 【" + elementArr[i] + "】 is not legal");
                            break;
                    }
                    resultStack.push(result);
                }
            }
            return resultStack;
        },
        //把中綴表達(dá)式轉(zhuǎn)為后綴表達(dá)式，再計算
        calculateByPostfixExpression: function(expression) {
            var elementArr = this.infixToPostfixExpression(expression).split(" ");
            var size = elementArr.length;
            var resultStack = [];
            for(var i = 0; i < size; i++) {
                if(Bee.StringUtils.isNumeric(elementArr[i])) {
                    //如果是數(shù)值
                    resultStack.push(elementArr[i]);
                } else {
                    var operand1 = resultStack.pop();
                    var operand2 = resultStack.pop();
                    var result;
                    switch(elementArr[i]) {
                        case "+":
                            result = Bee.ElementaryArithmeticUtils.add(operand2, operand1);
                            break;
                        case "-":
                            result = Bee.ElementaryArithmeticUtils.subtract(operand2, operand1);
                            break;
                        case "×":
                        case "*":
                            result = Bee.ElementaryArithmeticUtils.multiply(operand2, operand1);
                            break;
                        case "/":
                        case "÷":
                            result = Bee.ElementaryArithmeticUtils.divide(operand2, operand1);
                            break;
                        default:
                            result = "";
                            alert("The operator 【" + elementArr[i] + "】 is not legal");
                            break;
                    }
                    resultStack.push(result);
                }
            }
            return resultStack;
        },
        //橫式計算
        horizontalCalculation: function(expression) {
            expression = Bee.StringUtils.deleteWhitespace(expression);
            expression = this.eliminatePositiveOrNegativeSign(expression);
            var result = expression;
            while(expression.indexOf("(") >= 0) {
                expression = expression.replace(/([^()]+)/g, function(matchStr) {
                    return eval(matchStr);
                });
                result += "=" + expression;
            }
            while(expression.indexOf("[") >= 0) {
                expression = expression.replace(/[[^[]]+]/g, function(matchStr) {
                    return eval(matchStr);
                });
                result += "=" + expression;
            }
            while(expression.indexOf("{") >= 0) {
                expression = expression.replace(/{[^{}]+}/g, function(matchStr) {
                    return eval(matchStr);
                });
                result += "=" + expression;
            }
            var pattern = /(?:[1-9]d*|0)(?:.d+)?[*/](?:[1-9]d*|0)(?:.d+)?/;
            while(expression.indexOf("*") >= 0 || expression.indexOf("/") >= 0) {
                expression = expression.replace(pattern, function(matchStr, index) {
                    return eval(matchStr);
                });
                result += "=" + expression;
            }
            if(/[-+*/]/.test(expression)) {
                result += "=" + eval(expression);
            }
            return result;
        },
        //豎式計算
        verticalCalculation: function(expression) {
            var result = this.horizontalCalculation(expression);
            return result.replace(/=/g, "
$&");
        }
    };