Mask javascript variable value

There is a similar question (Javascript phone mask for text field with regex).

You can do it using regular expressions (see the code working at http://jsfiddle.net/BBeWN/45/):

var value = '1234567';
var formatted = value.replace(/^(\d{3})(\d{4}).*/, '$1-$2');

Notice that each part of the regular expression that is wrapped within parenthesis, (\d{3}) and (\d{4}) in the example above, can then be referenced to build the formatted text string using $1 and $2 respectively.

If you have N parts of the regular expression wrapped within parenthesis, you would be able to reference them to build a formatted text string with $1, $2, ..., $N respectively.

So, for the other format you mention ((000) 000-0000), the code would be like this:

var formatted = value.replace(/^(\d{3})(\d{3})(\d{4}).*/, '($1) $2-$3');

You can find a great JavaScript regular expressions reference at https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions

There is a javascript library that provides a solution for this problem:

https://github.com/the-darc/string-mask

And you don't need to create a new regular expression every time you change your mask(Format).

You can use it just like that:

var formatter = new StringMask("(000) 000-0000", { reverse: true });
var result = formatter.apply('123456789'); // (012) 345-6789

or

var formatter = new StringMask('#.##0,00', { reverse: true });
var result = formatter.apply('123456789'); // 1.234.567,89