Javascript Regex to match only a single occurrence no more or less

You can do this

/^[^-]+-[^-]+$/

^ depicts the start of the string

$ depicts the end of the string

[^-]+ matches 1 to many characters except -

Weird (and not a Regex)... but why not?

2 === str.split("-").length;

/^[^-]*-[^-]*$/

Beginning of string, any number of non-hyphens, a hyphen, any number of non-hyphens, end of string.

You could use a combination of indexOf and lastIndexOf:

String.prototype.hasOne = function (character) {
    var first = this.indexOf(character);
    var last = this.lastIndexOf(character);

    return first !== -1 &&
        first === last;
};

'single-hyphen'.hasOne('-'); // true
'a-double-hyphen'.hasOne('-'); // first !== last, false
'nohyphen'.hasOne('-'); // first === -1, false

http://jsfiddle.net/cSF8T/