eval addition with -1 doesn't work
Question by David 天宇 Wong
I’m having trouble with this js code:
$('.downvoted').live('click',function(){
var ele = $(this);
var truc = ele.prev('.score_position');
$.post('ajax/vote.php', { vote :ele.attr('title') }, function(data) {
if(data == 'done'){
ele.removeClass('downvoted').addClass('downvote').html('<img src="images/down.png" />');
truc.html(eval(truc.html()+1));
}
});
return false;
});
so I have this same function 3 other times for downvoting, un-upvoting and upvoting. It works well except with one exception, if truc.html() is -1 then it goes to -11 instead of 0.
Any idea why it doesn’t work? (you guys can try it here: http://91.121.154.130/?sort=last&# with id:azerty pw:azerty)
Answer by Elliot Bonneville
Don’t use eval() for this sort of work! Use parseInt, Number(...), or any of the other numerous ways of converting a value to a number in Javascript.
truc.html(parseInt(truc.html(), 10) + 1);
Note the second parameter in the parseInt function. This means you want the value passed into be parsed as a base-10 number. If you pass in a number starting with 0 into the parseInt function without specifying the radix you’ll get an unexpected and unwanted result.
Or
truc.html(Number(truc.html())+1);
Or even this:
truc.html(truc.html()*1 + 1);
This works because multiplying a string number by one results converts the variable to a number. Be careful– if the variable you multiply isn’t a valid number you’ll get NaN!
The reason you can’t simply do truc.html(truc.html()+1); is because .html() returns a string value. If you add a number to a string in Javascript, the number is simply concatenated to the string, and no math is performed. (e.g. “-1” + “1” equals “-11”).
Answer by Starx
You need to make sure the value is an integer and Use of .text() is better on this case.
parseInt(truc.text(), 10)+1
