javascript - ES6 filter an array with Regex

Question

I'm trying to filter an array that contains a bunch of urls. I need to return the urls that only contain the word "contact".

For example there is a link https://www.example.com/v1/contact-us/ca

This should be returned from the filter.

I tried this:

    const regex = new RegExp("/contact", 'g' )
    sites.links.filter((val) => {

     console.log(regex.test(val.href))

    })

It currently just sends back false through all the domains, when I know there is one domain that contains the word "contact".

Answer 1

Firstly new RegExp('/contact', 'g'); is equivalent to //@contact@/g where the @ are backspace character (ASCII 08) ... clearly not what you want

So, you would do new RegExp('/\bcontact\b', 'g'); - this is equivalent to //contact/g

However, the \b after / is redundant

so ... down to //contact/g

Using string.match here as regex.test is misused. Below is the description

var sites = { 
    links: [
        {href: 'https://www.example.com/v1/contact-us/ca'},
        {href: 'https://www.example.com/v1/contact-us/au'},
        {href: 'https://www.example.com/v1/contact-us/us'},
        {href: 'https://www.example.com/v1/dontcontact-us/us'}
    ]
};

const regex = new RegExp('/contact\b', 'g');
const matchedSites = sites.links.filter(({href}) => href.match(regex));
console.log(matchedSites);

The next problem is using the ONE regex multiple times in a regexp.test with g flag. With each call, it will look from the next indexOf previous found substring and with consecutive calls on a same-type string, it basically will return true, false, true, false.

If you want to use regex.test, then don't re-use the same regex unless you know the consequences of doing so or do not use g flag (which here you do not need)

var sites = { 
    links: [
        {href: 'https://www.example.com/v1/contact-us/ca'},
        {href: 'https://www.example.com/v1/contact-us/au'},
        {href: 'https://www.example.com/v1/contact-us/us'},
        {href: 'https://www.example.com/v1/dontcontact-us/us'}
    ]
};

const regex = new RegExp('/contact\b', 'g');
const correctRegex = new RegExp('/contact\b');

const matchedSitesFailed = sites.links.filter(({href}) => regex.test(href));
const matchedSitesSuccess = sites.links.filter(({href}) => new RegExp('/contact\b', 'g').test(href));
const matchedSitesSuccess2 = sites.links.filter(({href}) => correctRegex.test(href));

console.log('failed returns:', matchedSitesFailed.length);
console.log('success returns:', matchedSitesSuccess.length);
console.log('success returns 2:', matchedSitesSuccess2.length);