Match dynamic string using regex

Question

I'm trying to detect an occurrence of a string within string. But the code below always returns "null". Obviously something went wrong, but since I'm a newbie, I can't spot it. I'm expecting that the code returns "true" instead of "null"

var searchStr = 'width'; 
var strRegExPattern = '/'+searchStr+'\b/'; 
"32:width: 900px;".match(new RegExp(strRegExPattern,'g'));

Answer 1

Please don't put '/' when you pass string in RegExp option

Following would be fine

var strRegExPattern = '\\b'+searchStr+'\\b'; 
"32:width: 900px;".match(new RegExp(strRegExPattern,'g'));

Answer 2

Notice that '\\b' is a single slash in a string followed by the letter 'b', '\b' is the escape code \b, which doesn't exist, and collapses to 'b'.

Also consider escaping metacharacters in the string if you intend them to only match their literal values.

var string = 'width';
var quotemeta_string = string.replace(/[^$\[\]+*?.(){}\\|]/g, '\\$1'); // escape meta chars
var pattern = quotemeta_string + '\\b';
var re = new RegExp(pattern);
var bool_match = re.test(input); // just test whether matches
var list_matches = input.match(re); // get captured results