Combining regular expressions in Javascript

Question

Is it possible to combine regular expressions in javascript.

For ex:

 var lower = /[a-z]/;
 var upper = /[A-Z]/;
 var alpha = upper|lower;//Is this          


        

Answer 1

If this is something you only need to do once or twice, I'd stick with doing it on a per-case basis as suggested by other answers.

If you need to do a lot, however, a couple of helper functions might improve readability. For example:

var lower = /[a-z]/,
    upper = /[A-Z]/,
    digit = /[0-9]/;

// All of these are equivalent, and will evaluate to /(?:a-z)|(?:A-Z)|(?:0-9)/
var anum1 = RegExp.any(lower, upper, digit),
    anum2 = lower.or(upper).or(digit),
    anum3 = lower.or(upper, digit);

And here's the code if you want to use those functions:

RegExp.any = function() {
    var components = [],
        arg;

    for (var i = 0; i < arguments.length; i++) {
        arg = arguments[i];
        if (arg instanceof RegExp) {
            components = components.concat(arg._components || arg.source);
        }
    }

    var combined = new RegExp("(?:" + components.join(")|(?:") + ")");
    combined._components = components; // For chained calls to "or" method
    return combined;
};

RegExp.prototype.or = function() {
    var args = Array.prototype.slice.call(arguments);
    return RegExp.any.apply(null, [this].concat(args));
};

The alternatives are wrapped in non-capturing groups and combined with the disjunction operator, making this a somewhat more robust approach for more complex regular expressions.

Note that you will need to include this code before calling the helper functions!