string.replace 用变量替换

我们平常对字符串进行替换的时候

//一次替换
var str="Welcome Microsoft!"
str.replace(/Microsoft/,"W3School") //Welcome W3School!
//只会替换找到的第一个

//全局替换
var str="Welcome to MicrosoftMicrosoft! ";
str.replace(/Microsoft/g,"W3School") //Welcome to W3SchoolW3School!

项目里遇到需要传入一个变量，然后在替换

var text="Microsoft";
var str="Welcome to MicrosoftMicrosoft! ";
str.replace(new RegExp(text,'g'),"W3School");//Welcome to W3SchoolW3School!