CASPERJS how to evaluate javascript function

Question

I started learning how to use casperJs. And have some troubles:

1. I want to select grid cell by innerHTML.

in my test I write method which should return selector of cell, but it always returns null.

function getAlertInGridByInnerHTML(htmlString) {
    var rezultCell = casper.evaluate(function () {
        var gridChilds = document.querySelector('div[id^="scheduler-alert-grid"]').getElementsByTagName('div');
        for (i = 0; i < gridChilds.length; i++) {
            var childDiv = gridChilds[i];
            if (childDiv.innerHTML == htmlString) {

                return childDiv;
            }
        }
    });
    return rezultCell;
};

I call this function in this way:

casper.test.begin('Test double click activity assigned alert', function suite(test) {
this.mouse.down(getAlertInGridByInnerHTML('BLUE ALERT'));
    casper.run(function () {
        test.done();
    });
});

maybe someone can explain where is problem? When I run same code (which is inside evaluate function div is find).