String functions in JavaScript by example

Apr 2, 2013 00:00 · 356 words · 2 minute read Programming JavaScript

You can capture the substring that has your desired pattern on a large string with expressions in JavaScript.

Some key point

\w will match with any word character

\d will match with any decimal digit

[] Is used to match with set of characteristics

{0} Is used to quantify a match i.e. {3} will match the first three characters.

() Make capturing group

\ will escape special character

Match all with groups

var someText = "this is some <italic> important </italic> html text with some numbers such as 1, 3 and 6";
var expression = /<italic> (.*) <\/italic>/;
var result = expression.exec(someText);
alert("matched string : " + result[0]);
alert("capture string: " + result[1]);

(.*) will capture anything that exists between tag in the text. It will return the result as an array that contain the matched string i.e. “ important ” along with the captured string I.e. “important”.

Check for the existence of a number

You can check if something exists in a string or not .

var numberExpression = /\d/;
var isContainNumber = numberExpression.test(someText);
alert("is the string contain number : " + isContainNumber);

“/\d/” will look for any number on a string and the “test” method is check it against a string. Therefore it will return “true” as our string contains numbers.

Character Replace

You can replace a set of substrings in a string that matches with your desired pattern with regular expressions.

var spaceBetweenTwoWords = /(\w+) (\w+)/g;

var updatedString = someText.replace(spaceBetweenTwoWords, function (match, group1, group2) {

    return group1.toUpperCase();


alert("replace each word with uppercase :" + updatedString);

(\w+) is the first capture group that looking for any word with one or more character that followed by a white space with the second capture group. The pattern is looking for any word that has one or more character which surrounded by a space.

The “match” is showing all the matches with our criteria while “group1” and “group2” is contained only odd or even words. In the above example it will return “ THIS some important HTML WITH NUMBERS AS,3 6”.


Feel free to download the full source code of this example from my github.