正則表達式中如何添加自定義變量

給正則表達式添加變量：

方法一： new RegExp

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"));

方法二： eval

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"));