Why Firefox Says That Window.Event Is Undefined? (Call Function with Added Event Listener)

Why Firefox says that window.event is undefined? (call function with added event listener)

try getting the event using the parameter passed (named e in this case). i tested this and both window.event and the e is supported in chrome.

try checking for both, whichever exists

var ex = {
  exampl: function(e){

    console.log(window.event);
    console.log(e);  

    //check if we have "e" or "window.event" and use them as "evt"
    var evt = e || window.event    

  }
}

Firefox window.event is undefined error

That's because it is. window.event is for older versions of IE.

The typical way to do this is:

function postBackByObject(e) {
    e = e || window.event;
    var o = e.srcElement || e.target;
    // ...
}

Workaround for Firefox's lack of window.event?

Here's an ugly hack, based on the assumption that all event listeners will ultimately be registered by the EventTarget.addEventListener() method. The "solution" below changes EventTarget's prototype (yuck!) so as to wrap all event listeners in a method that will assign the event to window.event before delegating to the actual listener.

const addEventListener = EventTarget.prototype.addEventListener;
EventTarget.prototype.addEventListener = function(name, handler) {  addEventListener.call(this, name, function(event) {    window.event = event;        handler(event);  })};
function clicked() {  // just demonstrating that window.event is set  console.log(window.event.target.innerHTML);}
document.getElementById('one').addEventListener('click', clicked);document.getElementById('two').addEventListener('click', clicked);

<button id="one">Test 1</button><button id="two">Test 2</button>

Type error: event is undefined in firefox about javascript

Remove the var from var event = window.event. The variable is already declared (as an argument), so re-declaring it with var can only lead to problems.

To be specific, due to hoisting, here is what your code boils down to:

function MouseDown(event) {
    var event; // = undefined
    if( !event) { // always true
        event = window.event; // undefined in modern browsers
    }
    X = event.pageX; // ERROR!
}

Without the var, all is well!

event.path is undefined running in Firefox

The path property of Event objects is non-standard. The standard equivalent is the composedPath method. But it was new when the question was asked (2016); it's well-established as of this update in January 2023.

So you may want to try composedPath and fall back to path (or just use composedPath now it's established):

// Written in ES5 for compatibility with browsers that weren't obsolete
// yet when the question was posted, although they are now
var path = event.composedPath ? event.composedPath() : event.path;
if (path) {
    // You got some path information
} else {
    // This browser doesn't supply path information
}

Obviously that won't give you path information if the browser doesn't supply it, but it allows for both the old way and the new, standard way, and so will do its best cross-browser.

Example:

// Written in ES5 for compatibility with browsers that weren't obsolete
// yet when the question was posted, although they are now
document.getElementById("target").addEventListener("click", function (e) {
    // Just for demonstration purposes
    if (e.path) {
        if (e.composedPath) {
            console.log("Supports `path` and `composedPath`");
        } else {
            console.log("Supports `path` but not `composedPath`");
        }
    } else if (e.composedPath) {
        console.log("Supports `composedPath` (but not `path`)");
    } else {
        console.log("Supports neither `path` nor `composedPath`");
    }

    // Per the above, get the path if we can, first using the standard
    // method if possible, falling back to non-standard `path`
    var path = event.composedPath ? event.composedPath() : event.path;

    // Show it if we got it
    if (path) {
        console.log("Path (" + path.length + ")");
        Array.prototype.forEach.call(path, function(entry) {
            console.log(entry === window ? "window" : entry.nodeName);
        });
    }
});

.as-console-wrapper {
    max-height: 100% !important;
}

<div id="target">Click me</div>

Javascript - e (event) is undefined in firefox

Change your handlers to this...

jQuery('.reallyNice_slider').each(function(){
    var slider = new reallyNiceSlider(this);

    if(document.addEventListener)
        document.addEventListener('mousemove', 
                                  function(e){
                                    slider.sliderMove(e, slider)
                                  }, false);
    else
        document.attachEvent('onmousemove', 
                             function(){
                               slider.sliderMove(window.event, slider)
                             });

    this.style.visibility = 'visible';
 });

Then change your functions to receive the event object as the first argument.

this.sliderMove = function(e, obj){
  //var e = window.event;  // remove this
    var range = obj.range;
    var offset, cursor={x:0,y:0}, diff={x:0,y:0,total:0,ratio:0}, opacity, max = range.max+obj.safe, child;
    var selectedObj = null;

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