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: 
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'));

```
You're mixing up the two ways of creating regexes in JavaScript. If you use a regex literal, `/` is the regex delimiter, the `g` modifier immediately follows the closing delimiter, and `\b` is the escape sequence for a word boundary:

```
var regex = /width\b/g;

```

If you create it in the form of a string literal for the RegExp constructor, you leave off the regex delimiters, you pass modifiers in the form of a second string argument, and you have to double the backslashes in regex escape sequences:

```
var regex = new RegExp('width\\b', 'g');

```

The way you're doing it, the `\b` is being converted to a backspace character before it reaches the regex compiler; you have to escape the backslash to get it past JavaScript's string-literal escape-sequence processing. Or use a regex literal.