How to obtain value from single line text box using javascript?

Hi thanks for helping me out.
I am trying to obtain the value from a single line text box using this.getTextValue().
What am I doing wrong?

Qualtrics.SurveyEngine.addOnReady(function()
{
/*Place your JavaScript here to run when the page is fully displayed*/
this.questionclick = function(event,element){
//alert('ID: ' +element.id);

var answer = this.getTextValue()
alert(answer);
}
});