只匹配javascript正则表达式中方括号中的数字，而不匹配上一个单词

Question

I've the following regex in javascript. I'm trying to match only the first number inside square brackets in a string, as i have to replace it. This is my code.

var str = 'dgt_gallery_item[3][type]'; 
var res = str.match(/^\w+\[(\d+)\]/g);
var rep = str.replace(/^\w+\[(\d+)\]/g, 5 + 1);

The idea is match from start 1 or more alphanumeric chars, then [, then start capturing 1 or more digits, then ].

I checked on regex 101 and my code looks correct but when i test it in the browser, it also matches the first word. How can i skip it?

Answer 1

You can use this regex:

var rep = str.replace(/(?!\[)\d/, (5+1));

---

Regex live here .

Explaining:

(?!\[)   # the number must be preceded by one '[' character
         # without taking it
\d       # takes a one digit number .. 
         # you can use '\d+' to multiple digits number

Answer 2

Javascript regex engine does not support Look Behind, so you need to do a little tweak here:

var str = 'dgt_gallery_item[3][type]';
var res = str.match(/(^\w+)\[(\d+)\]/g);
var rep = str.replace(/(^\w+)\[(\d+)\]/g, function(combinedMatch, pattern1, pattern2) {
    return pattern1 + "[" + 6 + "]";
});

Output: dgt_gallery_item[6][type]