How to use a variable within a regex in Javascript?

Question

I have a regular expression and would like to put a variable inside it. How do I do?

My code is this:

public regexVariable(vRegex: string, testSentences: Array<any> ) {
    const regex = new RegExp('/^.*\b(' + vRegex + ')\b.*$/');
    const filterSentece = testSentences.filter(result => {
        if (regex.test(result)) {
            return result
        })
}

Does this answer your question? How do you use a variable in a regular expression? — ggorlen
– ggorlen, Commented Mar 20, 2020 at 21:29
Don't forget to escape your backslashes in the string literal and remove the leading/trailing forward slashes. — ggorlen
– ggorlen, Commented Mar 20, 2020 at 21:37
A word of caution The '.*' at the beginning of the regex may not be what you intend it to be. As Regexes are greedy by default it has a high chance of capturing to much. So if you run in any problems try using '.*?' instead of '.*' to get non greedy behaviour. — Andreas Neumann
– Andreas Neumann, Commented Mar 20, 2020 at 22:08

Hashbrown · Accepted Answer · 2020-04-16 04:29:55Z

2

const regex = new RegExp(`^.*\\b(${vRegex})\\b.*$`);

You can use template literals (`, instead of "/') to build strings that you can interpolate expresions into; no more oldschool +ing.

The only thing that was an actual issue with your code, though, was the \b character class. This sequence is what you want RegExp to see, but you can't just write that, otherwise you're sending RegExp the backspace character.
You need to write \\b, which as you can see from that link, will make a string with a \ and an ordinary b for RegExp to interpret.

edited Apr 16, 2020 at 4:29

answered Mar 20, 2020 at 21:34

Hashbrown

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2 Comments

Felix Kling Over a year ago

Even better: String.raw`^.*\b${vRegex}\b.*$`. Also don't forget to explain why you changed the things you did.

Eduardo Vidal Borges Over a year ago

Thanks, it helped me

Kosh · Accepted Answer · 2020-03-20 21:35:04Z

1

You're almost there, just look at RegEx constructor

const regex = new RegExp('^.*\\b(' + vRegex + ')\\b.*$');

edited Mar 20, 2020 at 21:35

answered Mar 20, 2020 at 21:31

Kosh

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