来自字符串的正则表达式在 Javascript 中给出 null

Question

I have a string

let str = 'WordA<br>WordB';

I am using this expression /(\\S+)(?=<br>)/ to match characters before the <br> .

It works fine directly as a predefined function

let regex = /(\\S+)(?=<br>)/;

But when I try to build it using a string, it gives null everytime.

let rgs = "(\S+)(?=<br>)";
let regex = new RegExp(rgs);

How to use the regex as a string to obtain the same results.

Full code:

 let str = 'WordA<br>WordB'; let regex = /(\\S+)(?=<br>)/; let m = str.match(regex); console.log(m); console.log(m[1]); let rgs = ("(\\S+)(?=<br>)"); let regex2 = new RegExp(rgs); let m2 = str.match(regex2); console.log(m2); console.log(m2[1]);

Answer 1

When using regex in string via new RegExp() , you need to escape the backslash character:

 let str = 'WordA<br>WordB'; let regex = /(\\S+)(?=<br>)/; let m = str.match(regex); console.log(m); console.log(m[1]); let rgs = "(\\\\S+)(?=<br>)"; let regex2 = new RegExp(rgs); let m2 = str.match(regex2); console.log(m2); console.log(m2[1]);

Otherwise the "\\S" is translated to just "S" (as you are escaping the S character):

 console.log("S", "\\S", "\\\\S", "S" === "\\S");