Javascript RegExp Intro (part 1)

Aug 29, 2012

In its simplest form, regex can be used just like you would use a string in the String.replace method.

'somestring'.replace('s','-'); //yields -omestring
'somestring'.replace(/s/,'-'); //same
'somestring'.replace(new RegExp('s',''),'-'); //same

This works fine for alpha numeric characters, but some characters need to be escaped using \ because they have special meaning within a regular expression.

All of these examples can be run easily using your favorite browser's javascript console.

Before digging further into the regular expression itself, it's a good idea to understand how they can be used.

RegExp object usage

exec - returns the first match of the passed string in a new array, even if the global modifier is specified

new RegExp('h').exec('abcdefghij');   //["h"]
/h/.exec('abcdefghhj');               //["h"]
/h/g.exec('abcdefghhj');               //["h"]

test - returns true or false depending whether a match was found

new RegExp('h').exec('abcdefghij')  //true
new RegExp('x').exec('abcdefghij')  //false

String extension method usage

replace - replaces the first match (or all if using the global modifier) with the provided replacement string
```
'abcdefg'.replace(/c/,'-') //yields ab-cdefg
```
match - returns first match in an array (or all if using the global modifier)
```
'abcdecg'.match(/c/) //yields ['c']
'abcdecg'.match(/c/g) //yields ['c','c']
```