Javascript: Why Sometimes Alert() Does Not Work But Console.log() Does?

From time to time, I face a very intriguing bug. My javascript code does not display an alert(msg) during execution, but if I use a console.log(msg) it does show up in the console.

Solution 1:

This is a very common problem, and everyone has faced this problem atleast once. The reason alert() does not work is because previously you have checked "prevent this page from creating additional dialoug" checkbox.

lets take a look at this code.

<scripttype="text/javascript">var js_name = ['elem1', 'elem2']

 for (var i = 0; i < js_name.length; i++) {
    alert(js_name[i]);
 };

</script>

There will be two alert boxes if you run the code. If you check the "prevent this page from creating additional dialoug" checkbox and then refresh the page again you won't get alert box ever again.

Solution is you need to close that webpage and reopen again in the browser(don't need to close the entire browser). I am assuming you are using chrome. Internet Explorer or FireFox doesn't have this checkbox feature.

Solution 2:

If you override alert function so it won't work

alert = function() 
{
 ...
};

alert('hello') // won't show any alert

Solution 3:

To my knowledge alert() is always shown unless it is repetitive in which case you are asked if you want to continue showing alerts.

I suppose the specifics on how this is handled depends on your browser. Care to share any more details? :)

Solution 4:

This also happens in ColdFusion. If you use anywhere after the script tag a cflocation tag (instead of location.href) the alert will not show.

Solution 5:

This can also happen in Firefox if you have Dev Tools open and Responsive Design Mode enabled. It sounds like it's a bug.