From my reading here I would expect this code to work, but it doesn't. I have tried two ways to add click events to a button called "lonext". Neither work. I'm not sure why this might be?
window.onload = function() {
var goSC = function() { //go to the sucess criteria section
document.getElementsByClassName("guidance1").style.display = "none";
document.getElementsByClassName("guidance2").style.display = "";
alert("button clicked");
//first try
document.getElementById("lonext").addEventListener("click", function() {
goSC();
}, false);
//second try
document.getElementById("lonext").onclick = goSC;
}
The getElementsByClassName returns an NodeList because you could have many elements in your DOM with the same class, not a single element.
So:
var goSC = function() {
var guidance1 = document.getElementsByClassName("guidance1");
for (var i = 0; i < guidance1.length; i++) {
guidance[i].style.display = "none";
}
var guidance2 = document.getElementsByClassName("guidance2");
for (var i = 0; i < guidance2.length; i++) {
guidance[i].style.display = "";
}
alert("button clicked");
});
window.onload = function() {
document.getElementById("lonext").onclick = goSC;
};
which if you used jQuery could be simplified to:
$(function() {
$('#lonext').click(function() {
$('.guidance1').hide();
$('.guidance2').show();
});
});
I would also strongly recommend you using a javascript debugging tool such as FireBug or Chrome Developer toolbar to inspect your javascript code and see potential errors with it. The Console tab will contain valuable information about possible errors in your javascript code.
Related
I have few textarea on which I want to get the default text selected when I tabbing upon it.
For a single textarea I've found a script which I adapted to my situation but is not an elegant solution.
How can I shorten it.
<script type="text/javascript">
var textBox1 = document.getElementById("textarea_1");
var textBox2 = document.getElementById("textarea_2");
var textBox3 = document.getElementById("textarea_3");
textBox1.onfocus = function() {
textBox1.select();
// Work around Chrome's little problem
textBox1.onmouseup = function() {
// Prevent further mouseup intervention
textBox1.onmouseup = null;
return false;
};
};
textBox2.onfocus = function() {
textBox2.select();
textBox2.onmouseup = function() {
textBox2.onmouseup = null;
return false;
};
};
textBox3.onfocus = function() {
textBox3.select();
textBox3.onmouseup = function() {
textBox3.onmouseup = null;
return false;
};
};
</script>
You can add a dedicated class name and refactor the code to be more generic using class name as selector an make it work for multiple textareas like this:
// Add the class 'auto-selectable' to the desired <texarea/> elements
var textBoxes = document.getElementByClassName('auto-selectable');
for(var i = 0; i < textBoxes.length; i++) {
var textBox = textBoxes[i];
textBox.select();
// Work around Chrome's little problem
textBox.onmouseup = function() {
// Prevent further mouseup intervention
textBox.onmouseup = null;
return false;
};
}
a small correction to Plamen's answer: Elements not Element
var textBoxes = document.getElementsByClassName('auto-selectable');
instead of:
var textBoxes = document.getElementByClassName('auto-selectable');
Let's say I have several textareas, and I want to add event listener to each textarea. When I type inside a textarea, I need to console the value typed inside it. I just can't figure out how to refer "this" to each textarea called in looping when being added event listener. The code below results in "undefined" in the browser console. Maybe you can set it right. Appricated the help. Thank you very much.
window.addEventListener("load", function(){
var char_max_inputs = document.querySelectorAll('.char_max');
for (var i = 0; i < char_max_inputs.length; i++){
var max_char = char_max_inputs[i].getAttribute("max_char");
var counter_id = char_max_inputs[i].getAttribute("counter_id");
char_max_inputs[i].addEventListener("keyup", function(){count_char(counter_id, max_char);}, false);
}
});
function count_char(counter_id, max_char) {
console.log(this.value);
}
You can solve it like this by using Function.prototype.bind
window.addEventListener("load", function() {
var char_max_inputs = document.querySelectorAll('.char_max');
for (var i = 0; i < char_max_inputs.length; i++) {
var max_char = char_max_inputs[i].getAttribute("max_char");
var counter_id = char_max_inputs[i].getAttribute("counter_id");
char_max_inputs[i].addEventListener("keyup", count_char.bind(char_max_inputs[i], counter_id, max_char), false);
}
});
function count_char(counter_id, max_char) {
console.log(this.value);
}
<textarea class="char_max"></textarea>
<textarea class="char_max"></textarea>
<textarea class="char_max"></textarea>
this can be very confusing in JavaScript, if not read about properly. An excellent resource to understand it is here
UPDATE
As pointed out in the comments, the example using call and bind together was incomplete. Removing it.
Is there a way to get all javascript associated with an html element by class name returned in an array? Any suggestion as to how one would achieve doing this? Are there any node packages that would allow me to do something like this?
For example:
HTML
<div class="click_me">Click Me</div>
JS
$('.click_me').on('click', function() { alert ('hi') });
I would want something like (psuedo-code either on the client or server side):
function meta() {
let js = [];
js = getAllJavascriptByClassName('click_me');
console.log(js[0]);
}
Output of meta()
$('.click_me').on('click', function() { alert ('hi') });
This will pull out all event handlers of all elements of given class.
But these handlers must be attached using jquery.
function getAllEventHandlersByClassName(className) {
var elements = $('.' + className);
var results = [];
for (var i = 0; i < elements.length; i++) {
var eventHandlers = $._data(elements[i], "events");
for (var j in eventHandlers) {
var handlers = [];
var event = j;
eventHandlers[event].forEach(function(handlerObj) {
handlers.push(handlerObj.handler.toString());
});
var result = {};
result[event] = handlers;
results.push(result);
}
}
return results;
}
// demo
$('.target').on('click',function(event){
alert('firstClick handler')
});
$('.target').on('click',function(event){
alert('secondClick handler')
});
$('.target').on('mousedown',function(event){
alert('firstClick handler')
});
console.log(getAllEventHandlersByClassName('target'));
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class='target'> </div>
You can use getEventListeners() which is part of the chrome devtools but for employing client side, there's an possible-duplicate question that partially answers this: How to find event listeners on a DOM node when debugging or from the JavaScript code? which basically shows (in the second voted answer) that depending on how the events are set (javascript attribute, eventListener, jquery, other lib) there are different ways to retrieve the functions.
The Visual Event 2 program mentioned in the first question seems to be more of a library doing what the second answer is suggesting so maybe this will solve your problem.
If you are interested only in jQuery solution I may suggest you (I assume there is only one event per type, but you need to cycle on all instances):
function getAllJavascriptByClassName(className) {
var elem = $('.' + className);
var result = [];
$('.' + className).each(function(index, element) {
var resultObjs = jQuery._data(element, "events");
var partialResult = [];
var x = Object.keys(resultObjs).forEach(function(currentValue, index, array) {
partialResult.push(resultObjs[currentValue][0].handler.toString());
});
result.push(partialResult);
});
return result;
}
function meta() {
let js = [];
js = getAllJavascriptByClassName('click_me');
console.log(JSON.stringify(js, null, 4));
}
$(function () {
$('.click_me').on('click', function (e) {
alert('Click event: hi')
});
$('.click_me:last').on('keypress', function (e) {
alert('Keypress event: hi')
});
meta();
});
<script src="https://code.jquery.com/jquery-1.12.3.min.js"></script>
<div class="click_me">Click Me</div>
<div class="click_me">Click Me</div>
I would personally override addEventListener at the right places (meaning at the very top) with some safe guards.
UNfortunately jquery event handlers appear to be quite hard to read...
var element = document.getElementById("zou");
element.addEventListener("click", function(e) {
console.log("clicked from addevent");
});
element.addEventListener("mouseup", function(e) {
console.log("mouseup from addevent");
});
$(element).on("mousedown", function(e) {
console.log("mousedown from $")
});
console.log(element.getListeners());
<script>
window.eventStorage = {};
(function() {
var old = HTMLElement.prototype.addEventListener;
HTMLElement.prototype.addEventListener = function(a, b, c) {
if (!window.eventStorage[this]) {
window.eventStorage[this] = [];
}
var val = {
"event": a,
"callback": b
};
var alreadyRegistered = false;
var arr = window.eventStorage[this];
for (var i = 0; i < arr.length; ++i) {
if (arr.event == a && arr.callback == b) {
alreadyRegistered = true;
break;
}
}
if (!alreadyRegistered) {
arr.push(val);
}
old.call(this, a, b, c);
}
HTMLElement.prototype.getListeners = function() {
return window.eventStorage[this] || {};
}
}());
</script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="zou">click on me</div>
My script contains a link a element with href attribute of "#login" as below.
Login
I want to my Javascript function detect the "href" element in the link and execute. How can I do this? My Javascript function is
window.onload = function() {
document.getElementsByTagName("a[href=#login]").onclick = function(e) {
e.preventDefault();
alert("working");
}
}
Why have I seen no querySelector love in these answers?
If you want to use that CSS selector to grab your link, nothing is stopping you:
window.onload = function() {
document.querySelector("a[href='#login']").onclick = function(e) {
e.preventDefault();
alert("working");
}
}
Login
EDIT:
I saw in another answer that you believe there may be multiple links on a page that match that selector, in which case you'll need to loop through them:
window.onload = function() {
var links = document.querySelectorAll("a[href='#login']"),
//always create anonymous functions outside of a loop :)
click = function(e) {
e.preventDefault();
alert("working");
}, i;
for (i = 0; i < links.length; i++) {
links[i].onclick = click;
}
}
Login
Login
Try this:
Login
function getValue()
{
alert("working");
e.preventDefault();
}
FIDDLE
Your getElementsByTagName is treating it like a jquery selector, which it is not designed to do.
It would be much simpler to give the tag an id and use getElementById:
window.onload = function() {
document.getElementById("loginLink").onclick = function(e) {
e.preventDefault();
alert("working");
}
}
Login
If for whatever reason you cannot change the html and you want to do it this way you would need to get all a tags then loop through each one to test the href attribute. Note you need to use a.getAttribute("href") to get "#login", rather than just a.href which oftens give you an full URL:
window.onload = function() {
var aTags = document.getElementsByTagName("a");
for(var i = 0; i < aTags.length; i++) {
var a = aTags[i];
if(a.getAttribute("href") == "#login") {
a.onclick = function(e) {
e.preventDefault();
alert("working");
}
}
}
}
Login
Test
Login Again
I'm having trouble with some javascript which uses getElementById. It works fine in FF, Safari and Chrome, but IE(8 - haven't tried others) bails out.
The relevant bit of html is a div called topnav:
<div id="topnav">
... some HTML ...
<div>
<div id="sub_1" class="lowernav">
... some HTML ...
</div>
<div id="sub_2" class="lowernav">
... some HTML ...
</div>
In my javascript, I want to find topnav. The full code (up to where it bails) is this:
<script>
window.onload = init();
function init() {
// Show current menu
showCurrentMenu();
}
function showCurrentMenu() {
hideMenus(); // Hide all menus and then show the current one
topnav = document.getElementById('topnav');
... rest of code ...
}
function hideMenus() {
var divlist = document.getElementsByTagName('div');
for(var ii=0; ii<divlist.length; ii++) {
if(divlist[ii].className != divlist[ii].className.replace('lowernav','')) {
divlist[ii].className += ' hidden';
}
}
}
... then some other code it hasn't reached yet...
Am I doing something wrong here? It may well be something really obvious, but for the life of me, I can't see it! All advice is much appreciated.
ETA: Ok, here's the whole code, as it currently stands:
<script>
window.onload = init;
function init() {
// Show current menu
showCurrentMenu;
// Attach 'onmouseover' event to main menu items
topnav = document.getElementById('topnav');
// Get all items in list
var menulist = topnav.getElementsByTagName('a');
for(var ii=0; ii<menulist.length; ii++) {
menulist[ii].onmouseover = showMenu;
}
document.getElementById('mainHomeNav').onmouseout = restoreMenu;
}
function restoreMenu(e) {
var targ;
if (!e) var e = window.event;
if (e.target) targ = e.target;
else if (e.srcElement) targ = e.srcElement;
if (targ.nodeType == 3) // defeat Safari bug
targ = targ.parentNode;
if (targ.id == "mainHomeNav") {
showCurrentMenu;
}
}
function hideMenus() {
var divlist = document.getElementsByTagName('div');
for(var ii=0; ii<divlist.length; ii++) {
if(divlist[ii].className != divlist[ii].className.replace('lowernav','')) {
divlist[ii].className += ' hidden';
}
}
}
function showCurrentMenu() {
hideMenus;
topnav = document.getElementById('topnav');
// Get all items in list
var menulist = topnav.getElementsByTagName('a');
for(var ii=0; ii<menulist.length; ii++) {
if(menulist[ii].className != menulist[ii].className.replace('thisSection','')) {
var thisid = menulist[ii].id;
var thissubmenu = document.getElementById(thisid + '_sub');
thissubmenu.className = thissubmenu.className.replace(/hidden/g,'');
}
}
}
function showMenu() {
hideMenus;
// show this menu
var submenu_id = this.id + '_sub';
var submenu = document.getElementById(submenu_id);
submenu.className = submenu.className.replace(/hidden/g,'');
}
</script>
The problem is
window.onload = init();
This will call the init function immediately, and then use its return value as the page's onload function. You need:
window.onload = init;
which will call the init function only after the page has fully loaded.
I found the problem - I didn't have 'var' in front of 'topmenu'.
So instead of
topnav = document.getElementById('topnav');
it should have been
var topnav = document.getElementById('topnav');
Thanks everyone for the help.
Your problem lies in the following line:
window.onload = init(); // this will CALL init() and assign the return value
Since init doesn't return anything, window.onload will be undefined.
Now the reason for it not working in IE, but in other Browsers is that those other Browsers might already have parsed a part of the DOM and therefore the call to showCurrentMenu works.
But that could just as well break, since from a technical point of view the document is not guaranteed to be loaded, to fix that you have to assign the actual function reference to window.onload by doing:
window.onload = init;