JavaScript replace/regex

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.