Question

The page has a textbox, when the user focus on it, I want to make a calculation every two seconds by the value of it. If the user blurs the textbox, I want to stop this calculation.

Assume only float values can be entered by the user. I tried something but it doesnt work.

http://jsfiddle.net/TUNm4/1/

Added original code, so if the fiddle gets removed we can still see what the issue was:

$(function() {
    var newValue = "";
    var makeCalculation = function(var1) {
        newValue = var1 * 0.05;
    };

    $("#textBox").focus(function() {
        (function() {
            makeCalculation(parseFloat($(this.val())))
            setTimeout(arguments.callee, 2000);
        });
    });
});

Answer 1

Check this fiddle: http://jsfiddle.net/TUNm4/6/

$(function() {

    var newValue = "";
    var makeCalculation = function(_this) {
        newValue = parseFloat($(_this).val()) * 0.05;
        $("div").html(newValue);
    };

    $("#textBox").focus(function(){
        makeCalculation(this);
        var _this = this;
        $(this).data("interval", setInterval(function(){
             makeCalculation(_this);   
        }, 2000));
    })
    .blur(function(){
         clearInterval($(this).data("interval")   );
    });

});

What you can also do, is onkeyup, then you always got the latest calculations and you don’t need the timeout:

$(function() {
    var newValue = "";    
    $("#textBox").bind("keyup change mouseup", function() {
        newValue = parseFloat($(this).val()) * 0.05;
        $("div").html(newValue);
    });
});