正则表达式里添加变量

function replace(str, before, after) {
    var reg = new RegExp(before, "g");
    return str.replace(reg, after);
}

var test =  ;
console.log(replace("A quick brown fox jumped over the lazy dog", "jumped", "leaped"));

function replace(str, before, after) {
    return str.replace(eval("/"+before+"/g"), after);
}

       
console.log(replace("A quick brown fox jumped over the lazy dog", "jumped", "leaped"));