Why does the following JavaScript Regular Expression Fail?

Asked Jan 31 '19 at 06:36

Active Jan 31 '19 at 06:36

Viewed 21 times

I was playing with JavaScript regular expression, and the following case really puzzled me.

let reg = /(\d{1,3}[.]){3}\d{1,3}/g;
let str = "123.23.2.2.2";
let results = str.match(reg);
console.log(results);

I was expecting results to be ['123.23.2.2', '23.2.2.2'], but in reality, the console.log(results) outputs ['123.23.2.2']. What did I do wrong? The global search tag /g should give me all the matched results. I am really puzzled right now. Somebody help me!

asked Jan 31 '19 at 06:36

totololo

2

Regex engines do not backtrack once they have found a successful match – Gurmanjot Singh Jan 31 '19 at 06:37
1

Because after matching '123.23.2.2', the remaining string is '.2', so it cannot match anymore – thang Jan 31 '19 at 06:39
Try let reg = /[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+/g – Kang Andrew Jan 31 '19 at 06:44
Yeah, after some digging, I sort of saw why it didn't work. I found this post very helpful: https://stackoverflow.com/questions/20833295/how-can-i-match-overlapping-strings-with-regex. – totololo Jan 31 '19 at 07:09
Thank you all for your answers. I was almost driven crazy by this puzzle. – totololo Jan 31 '19 at 07:11

Why does the following JavaScript Regular Expression Fail?

0 Answers0