SOURCE

// 实现一个计算器，求字符串的值，
// 例如((2 + (3 * 2) ) * (2 + 3) + (3 - 1) )
function cal(str) {
    str = str.replace(/\s/g, '')
    let arr = [...str]
    let stack = []
    let res = 0
    let cal = []
    for (let i = 0; i < arr.length; i++) {
        if (arr[i] === '(') {
            stack.push(arr[i])
        } else if (arr[i] === ')') {
            // 计算
            cal = []
            let cur = stack.pop()
            while (cur !== '(') {
                cal.unshift(cur)
                cur = stack.pop()
            }

            cal = cal.toString().replace(/\,/g, '')
            console.log(cal)
            res = eval(cal)
            stack.push(res)
        } else {
            stack.push(arr[i])
        }
    }
    return res
}
console.log(cal('((2 + (3 * 2) ) * (2 + 3) + (3 - 1) )'))

<div class="red blue green">hello world</div>

.red {
    color: red;
}
.green {
    color: green;
}
.blue {
    color: blue;
}