Javascript Regex replace first char only [duplicate]

Question

I'm sorry if I'm to noob to ask this, but I really dont have any idea with this.

Is there any idea for regex to replace a char that stand on the first? Example :

12
13
14
15
51
41
31
21

All data that had '1' on the first char, must be replaced to 'A', example:

A2
A3
A4
A5
51
41
31
21

Answer 1

In JavaScript :

var str = "12";
str = str.replace(/^1/, 'A');

In PHP :

$str = "12";
$str = preg_replace("/^1/","A",$str);

^ matches the start of the string.

Answer 2

It obviously wasn't clear enough: This is the regex to replace only the first character, but it can be any character in case you're coming here from a search engine. dystroy already responded to OP's answer completely.

In case anyone sees this thread and actually expects replace only the first char, you can do it using the following method:

var str = "12";
str = str.replace(/^./, 'A');
//A2

or PHP:

$string = "12";
$string = preg_replace("/^./", "A", $string);
//A2

This would turn *BCDEFG into ABCDEFG (* can be any character).