[javascript] Why does JavaScript only work after opening developer tools in IE once?

IE9 Bug - JavaScript only works after opening developer tools once.

Our site offers free pdf downloads to users, and it has a simple "enter password to download" function. However, it doesn't work at all in Internet Explorer.

You can see for yourself in this example.

The download pass is "makeuseof". In any other browser, it works fine. In IE, both buttons do nothing.

The most curious thing I've found is that if you open and close the developer toolbar with F12, it all suddenly starts to work.

We've tried compatibility mode and such, nothing makes a difference.

How do I make this work in Internet Explorer?

I put the resolution and fix for my issue . Looks like AJAX request that I put inside my JavaScript was not processing because my page was having some cache problem. if your site or page has a caching problem you will not see that problem in developers/F12 mode. my cached JavaScript AJAX requests it may not work as expected and cause the execution to break which F12 has no problem at all. So just added new parameter to make cache false.

$.ajax({
  cache: false,
});

Looks like IE specifically needs this to be false so that the AJAX and javascript activity run well.

I got yet another alternative for the solutions offered by runeks and todotresde that also avoids the pitfalls discussed in the comments to Spudley's answer:

        try {
            console.log(message);
        } catch (e) {
        }

It's a bit scruffy but on the other hand it's concise and covers all the logging methods covered in runeks' answer and it has the huge advantage that you can open the console window of IE at any time and the logs come flowing in.

It happened in IE 11 for me. And I was calling the jquery .load function. So I did it the old fashion way and put something in the url to disable cacheing.

$("#divToReplaceHtml").load('@Url.Action("Action", "Controller")/' + @Model.ID + "?nocache=" + new Date().getTime());

This solved my problem after I made a minor change to it. I added the following in my html page in order to fix the IE9 problem:

<script type="text/javascript">
    // IE9 fix
    if(!window.console) {
        var console = {
            log : function(){},
            warn : function(){},
            error : function(){},
            time : function(){},
            timeEnd : function(){}
        }
    }
</script>

If you are using angular and ie 9, 10 or edge use :

myModule.config(['$httpProvider', function($httpProvider) {
    //initialize get if not there
    if (!$httpProvider.defaults.headers.get) {
        $httpProvider.defaults.headers.get = {};    
    }    

    // Answer edited to include suggestions from comments
    // because previous version of code introduced browser-related errors

    //disable IE ajax request caching
    $httpProvider.defaults.headers.get['If-Modified-Since'] = 'Mon, 26 Jul 1997 05:00:00 GMT';
    // extra
    $httpProvider.defaults.headers.get['Cache-Control'] = 'no-cache';
    $httpProvider.defaults.headers.get['Pragma'] = 'no-cache';
}]);

To completely disable cache.

Besides the 'console' usage issue mentioned in accepted answer and others,there is at least another reason why sometimes pages in Internet Explorer work only with the developer tools activated.

When Developer Tools is enabled, IE doesn't really uses its HTTP cache (at least by default in IE 11) like it does in normal mode.

It means if your site or page has a caching problem (if it caches more than it should for example - that was my case), you will not see that problem in F12 mode. So if the javascript does some cached AJAX requests, they may not work as expected in normal mode, and work fine in F12 mode.

HTML5 Boilerplate has a nice pre-made code for console problems fixing:

// Avoid `console` errors in browsers that lack a console.
(function() {
    var method;
    var noop = function () {};
    var methods = [
        'assert', 'clear', 'count', 'debug', 'dir', 'dirxml', 'error',
        'exception', 'group', 'groupCollapsed', 'groupEnd', 'info', 'log',
        'markTimeline', 'profile', 'profileEnd', 'table', 'time', 'timeEnd',
        'timeStamp', 'trace', 'warn'
    ];
    var length = methods.length;
    var console = (window.console = window.console || {});

    while (length--) {
        method = methods[length];

        // Only stub undefined methods.
        if (!console[method]) {
            console[method] = noop;
        }
    }
}());

As @plus- pointed in comments, latest version is available on their GitHub page

I guess this could help, adding this before any tag of javascript:

try{
  console
}catch(e){
   console={}; console.log = function(){};
}

We ran into this problem on IE 11 on Windows 7 and Windows 10. We discovered what exactly the problem was by turning on debugging capabilities for IE (IE > Internet Options > Advanced tab > Browsing > Uncheck Disable script debugging (Internet Explorer)). This feature is typically checked on within our environment by the domain admins.

The problem was because we were using the console.debug(...) method within our JavaScript code. The assumption made by the developer (me) was I did not want anything written if the client Developer Tools console was not explicitly open. While Chrome and Firefox seemed to agree with this strategy, IE 11 did not like it one bit. By changing all the console.debug(...) statements to console.log(...) statements, we were able to continue to log additional information in the client console and view it when it was open, but otherwise keep it hidden from the typical user.

Here's another possible reason besides the console.log issue (at least in IE11):

When the console is not open, IE does pretty aggressive caching, so make sure that any $.ajax calls or XMLHttpRequest calls have caching set to false.

For example:

$.ajax({cache: false, ...})

When the developer console is open, caching is less aggressive. Seems to be a bug (or maybe a feature?)

If you are using AngularJS version 1.X you could use the $log service instead of using console.log directly.

Simple service for logging. Default implementation safely writes the message into the browser's console (if present).

https://docs.angularjs.org/api/ng/service/$log

So if you have something similar to

angular.module('logExample', [])
  .controller('LogController', ['$scope', function($scope) {
    console.log('Hello World!');
 }]);

you can replace it with

angular.module('logExample', [])
  .controller('LogController', ['$scope', '$log', function($scope, $log) {
    $log.log('Hello World!');
 }]);

Angular 2+ does not have any built-in log service.