how highlight few words in a freetextbox before the text is loaded to the freetextbox

$("[id$='_tbSearch']").highlight('HIGHLIGHT TEXT', "highlight");

jQuery.fn.highlight = function (str, className) {
    var regex = new RegExp(str, "gi");
    return this.each(function () {
        this.innerHTML = this.innerHTML.replace(regex, function (matched) {
            return "<span style="background-color:yellow;border:0px solid gray;">" + matched + "</span>";
        });
    });
};