var s = '($目标值+$权重-0.2)*100/20+10';
s = s.replace(/\$/g, ''); //去掉$符号
var ar = s.split('');

function in_array(k, arr) {
    for (var i = 0; i < arr.length; i ++) if (arr[i].toString() == k) return true;
    return false;
}

var sep = ['(', ')', '+', '-', '*', '/'];

var result = [], flag = false; //flag变量指示上一个字符是否为分隔符
for (var i = 0; i < ar.length; i ++) {
    if (in_array(ar[i], sep)) {
        result.push(ar[i]);
        flag = true;
    }
    else {
        if (flag) result.push(ar[i]);
        else result.length == 0 ? result.push(ar[i]) : result[result.length - 1] += ar[i].toString();
        flag = false;
    }
}

alert(result);