I have the following:

    var1 = "www.asite.page.co.uk";
    var2 = '.' + var1.match(/\w*\.\w*$/) [0];

I understand that it's trying to achieve ".co.uk", but I have no idea what the [0] does. Is it error handling?

I have the following:

    var1 = "www.asite.page.co.uk";
    var2 = '.' + var1.match(/\w*\.\w*$/) [0];

I understand that it's trying to achieve ".co.uk", but I have no idea what the [0] does. Is it error handling?

• javascript
• regex
• match

4 Answers 4

match returns an array of strings.

Without the global flag, the array is posed as follows:

• Only the first match is used.
• The first key, [0], contains the full first match.
• The other keys contains the matched groups within the first match.

Example:

var string = 'abc_123_abd_456';
var regexp = /_([0-9])/; // Matches an underscore, and groups a number
var match = string.match(regexp);
// match[0] = _1 (full match)
// match[1] = 1  (group)

When the global flag is specified, the array consists of all full matches:

var string = 'abc_123_abd_456';
var regexp = /_([0-9])/g; // Matches an underscore, and groups a number, GLOBAL
var match = string.match(regexp);
// match[0] = _1 (first full match)
// match[1] = _4 (second full match)

I remend to have a look at:

• MDN: RegExp

The match method returns an array of matches, so the [0] gets the first element of that array -- i.e. just the full match.

See the documentation for match or Rob W's answer for a more plete description.

See RobW's answer for plete and accurate reference.

The match method returns an array.

The match() method searches for a match between a regular expression and a string, and returns the matches.
This method returns an array of matches, or null if no match is found.

The [0] is used to return only the first element.

When you need one single string, it's often practical to use replace rather than match:

 var1 = "www.asite.page.co.uk";
 var2 = '.' + var1.replace(/.+?(\w*\.\w*)$/, '$1'); // .co.uk

BTW, your expression doesn't look right to me. A better way to match TLD would be something like

(\.[a-z]+\.[a-z][a-z]|\.[a-z]{3,})$

which matches both '.co.uk' and '.'. Example:

tld = "site.co.uk".replace(/.+?(\.[a-z]+\.[a-z][a-z]|\.[a-z]{3,})$/, '$1'); // .co.uk
tld = "yyy.".replace(/.+?(\.[a-z]+\.[a-z][a-z]|\.[a-z]{3,})$/, '$1'); // .