如何在没有eval的情况下在javascript中编写计算器

Question

所以,我搜索了高低,我找不到答案.我已经尝试了大约三次,并通过基本上将输入作为字符串存储在数组中,解析数字,然后打开运算符,以便评估整数,得到一个基本的一个,但我有一个找出链接逻辑真的很难.有没有人有什么建议？甚至可能只是伪造的代码？我真的不想使用eval.非常感谢

Answer 1

对于只有5个运算符(^,*,/,+, - )且没有括号的简单计算器,您可以执行类似的操作.首先,将字符串转换为数字和运算符数组很方便.然后,我们按照优先顺序遍历数组查找每个运算符,并将运算符应用于它之前和之后的数字.

function parseCalculationString(s) {
    // --- Parse a calculation string into an array of numbers and operators
    var calculation = [],
        current = '';
    for (var i = 0, ch; ch = s.charAt(i); i++) {
        if ('^*/+-'.indexOf(ch) > -1) {
            if (current == '' && ch == '-') {
                current = '-';
            } else {
                calculation.push(parseFloat(current), ch);
                current = '';
            }
        } else {
            current += s.charAt(i);
        }
    }
    if (current != '') {
        calculation.push(parseFloat(current));
    }
    return calculation;
}

function calculate(calc) {
    // --- Perform a calculation expressed as an array of operators and numbers
    var ops = [{'^': (a, b) => Math.pow(a, b)},
               {'*': (a, b) => a * b, '/': (a, b) => a / b},
               {'+': (a, b) => a + b, '-': (a, b) => a - b}],
        newCalc = [],
        currentOp;
    for (var i = 0; i < ops.length; i++) {
        for (var j = 0; j < calc.length; j++) {
            if (ops[i][calc[j]]) {
                currentOp = ops[i][calc[j]];
            } else if (currentOp) {
                newCalc[newCalc.length - 1] = 
                    currentOp(newCalc[newCalc.length - 1], calc[j]);
                currentOp = null;
            } else {
                newCalc.push(calc[j]);
            }
            console.log(newCalc);
        }
        calc = newCalc;
        newCalc = [];
    }
    if (calc.length > 1) {
        console.log('Error: unable to resolve calculation');
        return calc;
    } else {
        return calc[0];
    }
}
var calculateButton = document.getElementById('calculate'),
    userInput = document.getElementById('userInput'),
    result = document.getElementById('result');
calculateButton.addEventListener('click', function() {
    result.innerHTML = "The answer is " + calculate(parseCalculationString(userInput.value));
});

<input type="text" id="userInput" />
<input type="button" value="Calculate" id="calculate" />
<div id="result"></div>

(jsfiddle).要允许括号,您可以告诉calculate函数在开始查找任何其他运算符之前检查括号,然后在每组括号内的表达式上递归调用自身.还可以改进解析功能,例如移除任何空白区域并处理错误.