Consider a JavaScript program that uses nested loops like this:

    var i = 0;

    for (var j = 0; j < 10; j++) {

        testLoop:

        while (i < 10) {

            i++;

            log.appendChild(p("Inner loop: i = " + i + ", j = " + j));

            continue testLoop;

        }

    }

In this simple example, continue breaks to the while loop labelled with "testLoop". In JavaScript, an identifier used with continue can only reference a looping labeled statement (an
IterationStatement).

YUI Test Coverage would instrument the above labelled statement in this manner:

        testLoop:

        _yuitest_coverline();

        while (i < 10) {

            _yuitest_coverline();

            i++;

            _yuitest_coverline();

            log.appendChild(p("Inner loop: i = " + i + ", j = " + j));

            _yuitest_coverline();

            continue testLoop;

            _yuitest_coverline();

        }

In this example, the testLoop label no longer references the while loop. This code is syntactically incorrect and will raise a SyntaxError at parse time.

For an interactive example, see: http://jsfiddle.net/reid/psphd/1/

For more about the behavior of the continue statement, see ECMA-262 Sec. 12.7, 3rd or 5th Edition or MDN's JS label reference.

Easy to read MDN reference: http://_Sdeveloper.mozilla.org/en/JavaScript/Reference/Statements/label

This bug prevents YUI's selector-css2 module from being used with YUI Test Coverage.

We use a labelled looping statement here: http://_Sgithub.com/yui/yui3/blob/master/build/selector-css2/selector-css2.js#L172