JavaScript replace/regex

Question

Given this function:

function Repeater(template) {

    var repeater = {

        markup: template,

        replace: function(pattern, value) {
            this.markup = this.markup.replace(pattern, value);
        }

    };

    return repeater;

};

How do I make this.markup.replace() replace globally? Here's the problem. If I use it like this:

alert(new Repeater("$TEST_ONE $TEST_ONE").replace("$TEST_ONE", "foobar").markup);

The alert's value is "foobar $TEST_ONE".

If I change Repeater to the following, then nothing in replaced in Chrome:

function Repeater(template) {

    var repeater = {

        markup: template,

        replace: function(pattern, value) {
            this.markup = this.markup.replace(new RegExp(pattern, "gm"), value);
        }

    };

    return repeater;

};

...and the alert is $TEST_ONE $TEST_ONE.

Answer 1

You need to double escape any RegExp characters (once for the slash in the string and once for the regexp):

  "$TESTONE $TESTONE".replace( new RegExp("\\$TESTONE","gm"),"foo")

Otherwise, it looks for the end of the line and 'TESTONE' (which it never finds).

Personally, I'm not a big fan of building regexp's using strings for this reason. The level of escaping that's needed could lead you to drink. I'm sure others feel differently though and like drinking when writing regexes.