CODEWITHSUNDEEP
javascriptregex
georg
georg

Reputation: 214979

Match every second character

How can I match every second character in a string with a regular expression:

'abcdef'.match(???) => ['a', 'c', 'e']

I have this non-regex solution:

spl = []; for(var i = 0; i < str.length; i += 2) spl.push(str.charAt(i));

but looking for something more elegant.

Upvotes: 3

Views: 4559

Answers (4)

Fabr&#237;cio Matt&#233;
Fabr&#237;cio Matt&#233;

Reputation: 70159

You can do this without regex as well.

'abcdef'.split("").filter(function(v, i){ return i % 2 === 0; });

If IE<=8 support is an issue, you may add this polyfill.

Another solution, more verbose but with better performance which doesn't require shims:

var str = "abcdef", output = [];
for (var i = 0, l = str.length; i < l; i += 2) {
    output.push(str.charAt(i));
}

JSPerf

Upvotes: 5

Elias Van Ootegem
Elias Van Ootegem

Reputation: 76405

Using Array.prototype.map is an option, too:

var oddChars = Array.prototype.map.call('abcdef', function(i,k)
{
    if (k%2===0)
    {
        return i;
    }
}).filter(function(x)
{
    return x;
    //or if falsy values are an option:
    return !(x === undefined);
});

oddChars is now ["a","c","e"]...

Upvotes: 2

raina77ow
raina77ow

Reputation: 106385

Another possible approach:

'abcdefg'.replace(/.(.)?/g, '$1').split('');

It doesn't require any shims.

Upvotes: 7

T.J. Crowder
T.J. Crowder

Reputation: 1074575

You can use ..? and the ES5 map function (which can be supplied by a shim for browsers that don't yet have it natively):

"abcde".match(/..?/g).map(function(value) { return value.charAt(0); });
// ["a", "c", "e"]

Upvotes: 3

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