【小程序】eval被禁，代替方法

之前写的计算器小程序

昨天发现不好用了
调试下发现竟然报错说eval不能用了：

eval is not a function

原来eval方法被小程序禁掉了。

---

解决方法:
引入rpn.js 用里面的 calCommonExp(str)方法代替原来的eval(str)

rpn的github:
https://github.com/huruji/rpn.js

在小程序对应的js中，引入rpn：

注意，rpn.js想要模块化引入，需要我们手动修改下rpn.js的源码，在尾部把calCommonExp方法export出去方便外部引用:

module.exports = {  calCommonExp: calCommonExp}

这样直接调用rpn.calCommonExp()就可以完全代替原来eval()的位置。

---

rpn.js源码如下，万一你访问不了gayhub,我这有一份改完的:

function isOperator(value) {    var operatorString = '+-*/()×÷';    return operatorString.indexOf(value) > -1;}function getPrioraty(value) {    if(value == '-' || value == '+') {        return 1;    } else if(value == '*' || value == '/' || value == '×' || value == '÷' ) {        return 2;    } else{        return 0;    }}function prioraty(v1, v2) {    return getPrioraty(v1) <= getPrioraty(v2);}function outputRpn(exp) {    var inputStack = [];    var outputStack = [];    var outputQueue = [];    var firstIsOperator = false;    exp.replace(/\s/g,'');    if(isOperator(exp[0])){        exp = exp.substring(1);        firstIsOperator = true;    }    for(var i = 0, max = exp.length; i < max; i++) {        if(!isOperator(exp[i]) && !isOperator(exp[i-1]) && (i != 0)) {            inputStack[inputStack.length-1] = inputStack[inputStack.length-1] + exp[i] + '';        } else {            inputStack.push(exp[i]);        }    }    if(firstIsOperator) {        inputStack[0] = -inputStack[0]     }    while(inputStack.length > 0) {        var cur = inputStack.shift();        if(isOperator(cur)) {            if (cur == '(') {                outputStack.push(cur);            } else if (cur == ')') {                var po = outputStack.pop();                while(po != '(' && outputStack.length > 0) {                    outputQueue.push(po);                    po = outputStack.pop();                }            } else {                while(prioraty(cur,outputStack[outputStack.length - 1]) && outputStack.length > 0) {                    outputQueue.push(outputStack.pop());                }                outputStack.push(cur)            }        } else {            outputQueue.push(Number(cur));        }    }    if(outputStack.length > 0){        while (outputStack.length > 0) {            outputQueue.push(outputStack.pop());        }    }    return outputQueue;}function calRpnExp(rpnArr) {    var stack = [];    for(var i = 0, max = rpnArr.length; i < max; i++) {        if(!isOperator(rpnArr[i])) {            stack.push(rpnArr[i]);        } else {            var num1 = stack.pop();            var num2 = stack.pop();            if(rpnArr[i] == '-') {                var num = num2 - num1;            } else if(rpnArr[i] == '+') {                var num = num2 + num1;            } else if(rpnArr[i] == '*' || rpnArr[i] == '×') {                var num = num2 * num1;            } else if(rpnArr[i] == '/' || rpnArr[i] == '÷') {                var num = num2/num1;            }            stack.push(num);        }    }    return stack[0];}function calCommonExp(exp) {    var rpnArr = outputRpn(exp);    return calRpnExp(rpnArr)}//已经添加完export，在外面直接调用module.exports = {  calCommonExp: calCommonExp}