JavaScript中怎么代替eval的计算方法

Question

5+4-2+7*3/2  我要计算这个字符串，先乘除后加减 不用eval怎么写  各位大神给个思路。

Answer 1

(new Function("return 5+4-2+7*3/2"))();

Answer 2

eval("var a = 5+4-2+7*3/2;")

Answer 3

大概像這樣
var expressionCalc = (function () {    var operatorTable;    operatorTable = {
        '-': {
            priority: 1,
            handle: function (a, b) {
                return a - b;
            }
        },
        '+': {
            priority: 1,
            handle: function (a, b) {
                return a + b;
            }
        },
        '*': {
            priority: 2,
            handle: function (a, b) {
                return a * b;
            }
        },
        '/': {
            priority: 2,
            handle: function (a, b) {
                return a / b;
            }
        }
    };    function postfix(expression) {
        var i, op, stack, output, n, char;        stack = [];
        output = [];        //去空白
        expression = expression.replace(/\s/g, '');        function getn() {
            var n, c;            n = '';            while ((c = expression[i]) && /\w/.test(c)) {
                n += c;
                i++;
            }            i--;            return n;
        }
        function popstack(tobrace) {
            var o;            while (stack.length) {
                if (tobrace) {
                    o = stack.pop();
                    if (o == '(') {
                        break;
                    }
                    output.push(o);
                } else if (operatorTable[stack[stack.length - 1]] && operatorTable[stack[stack.length - 1]].priority >= op) {
                    output.push(stack.pop());
                } else {
                    break;
                }
            }
        }        for (i = 0; i < expression.length; i++) {
            char = expression[i];            if (char == ")") {
                popstack(true);
            } else if (char == "(") {
                stack.push(char);
            } else if (operatorTable[char] && (op = operatorTable[char].priority)) {
                popstack();
                stack.push(char);
            } else {
                output.push(getn());
            }
        }        op = -1;
        popstack();        return output;
    }    function calcStack(stack) {        var n1, n2, r, output;        if (!stack.length) return;        output = [];        for (i = 0; i < stack.length; i++) {
            n = stack[i];            if (operatorTable[n]) {
                n2 = new Number(output.pop());
                n1 = new Number(output.pop());                output.push(operatorTable[n].handle(n1, n2));
            } else {
                output.push(stack[i]);
            }
        }        return output[0];
    }    return function (expression) {
        return calcStack(postfix(expression));
    }
})();console.log(expressionCalc('5+4-2+7*3/2'));  //17.5

Answer 4

https://github.com/ougege/utils/blob/master/weCal.js  解决了多级括号和用户连续输入多个运算符