Question

$(function() {

    var div  = $('div');

    $('input').click(function() {
        if($(this).is(':checked')) {
            div.html(div.text() += 49);    
        } else {
            div.html(div.text() -= 49);      
        }
    });

});

This is crazy, for some reason the += and -= flag up bad assignment, why so?

By the way, I’m not using this code for anything, I know its bad, I’m just testing the +=

Example! http://jsfiddle.net/dD73X/

Answer 1

You cannot assign something to a temporary result. Use + and - instead. Also, there would be no need to assign with the compound operators because div.html(...) does exactly that: it replaces the text of the div with the result of the addition/subtraction.

Update: It seems that you also want to do integer addition (instead of string concatenation). You ‘d need to include parseInt as well for that, making the code:

 $('input').click(function() {
    if($(this).is(':checked')) {
        div.html(parseInt(div.text()) + 49);
    } else {
        div.html(parseInt(div.text()) - 49);
    }
});