Match exact string

What is the regular expression (in JavaScript if it matters) to only match if the text is an exact match? That is, there should be no extra characters at other end of the string.

For example, if I'm trying to match for abc, then 1abc1, 1abc, and abc1 would not match.

Use the start and end delimiters: ^abc$

It depends. You could

string.match(/^abc$/)

But that would not match the following string: 'the first 3 letters of the alphabet are abc. not abc123'

I think you would want to use \b (word boundaries):

var str = 'the first 3 letters of the alphabet are abc. not abc123';
var pat = /\b(abc)\b/g;
console.log(str.match(pat));

Live example: http://jsfiddle.net/uu5VJ/

If the former solution works for you, I would advise against using it.

That means you may have something like the following:

var strs = ['abc', 'abc1', 'abc2']
for (var i = 0; i < strs.length; i++) {
    if (strs[i] == 'abc') {
        //do something 
    }
    else {
        //do something else
    }
}

While you could use

if (str[i].match(/^abc$/g)) {
    //do something 
}

It would be considerably more resource-intensive. For me, a general rule of thumb is for a simple string comparison use a conditional expression, for a more dynamic pattern use a regular expression.

More on JavaScript regexes: https://developer.mozilla.org/en/JavaScript/Guide/Regular_Expressions

"^" For the begining of the line "$" for the end of it. Eg.:

var re = /^abc$/;

Would match "abc" but not "1abc" or "abc1". You can learn more at https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions