Transform any JavaScript function into a page event - javascript

I need to be able to achieve the following (one way or another):
function ShowContent() {}
document.onShowContent = function ()
{
// anything I want to happen....
}
What I'm trying to do is to add a kind of listener to me Advertisement code on the page that will auto refresh the ad slot when a specific function is called. Instead of having that function "ShowContent()" directly refresh the ad code, I want the ad code to refresh if it detects that "ShowContent()" has been called.
Thanks.

Modern javascript libraries make this easy. You can do it "by hand" of course, but here's a quick example with jQuery
First, the listener
$(document).bind( 'ShowContent', function()
{
// anything you want
});
Then the trigger
$(document).trigger( 'ShowContent' );
You could even go this route if you want
function ShowContent()
{
$(document).trigger( 'ShowContent' );
}

Here is a quick sample i threw together
var ev = (function(){
var events = {};
return {
on: function(name, handler){
var listeners = (name in events) ? events[name] : (events[name] = []);
listeners.push(handler);
},
raise: function(name){
var listeners = events[name];
if (listeners) {
var i = listeners.length;
while (i--) {
listeners[i]();
}
}
}
};
})();
// add a listener
ev.on("foo", function(){
alert("bar");
});
If you cannot manually alter the method in question to trigger the event, then you can 'wrap' it.
function methodIHaveNoControlOver(){
....
}
// intercept the call
var originalFn = methodIHaveNoControlOver;
// here we replace the FunctionDeclaration with a FunctionExpression containing a reference to the original FunctionDeclaration
methodIHaveNoControlOver = function(){
originalFn();
ev.raise("foo");
};
But note that this will not work if methodIHaveNoControlOver uses this to reference anything; so that will require more work.

Related

How to detect a window url change? [duplicate]

How can I check if a URL has changed in JavaScript? For example, websites like GitHub, which use AJAX, will append page information after a # symbol to create a unique URL without reloading the page. What is the best way to detect if this URL changes?
Is the onload event called again?
Is there an event handler for the URL?
Or must the URL be checked every second to detect a change?
I wanted to be able to add locationchange event listeners. After the modification below, we'll be able to do it, like this
window.addEventListener('locationchange', function () {
console.log('location changed!');
});
In contrast, window.addEventListener('hashchange',() => {}) would only fire if the part after a hashtag in a url changes, and window.addEventListener('popstate',() => {}) doesn't always work.
This modification, similar to Christian's answer, modifies the history object to add some functionality.
By default, before these modifications, there's a popstate event, but there are no events for pushstate, and replacestate.
This modifies these three functions so that all fire a custom locationchange event for you to use, and also pushstate and replacestate events if you want to use those.
These are the modifications:
(() => {
let oldPushState = history.pushState;
history.pushState = function pushState() {
let ret = oldPushState.apply(this, arguments);
window.dispatchEvent(new Event('pushstate'));
window.dispatchEvent(new Event('locationchange'));
return ret;
};
let oldReplaceState = history.replaceState;
history.replaceState = function replaceState() {
let ret = oldReplaceState.apply(this, arguments);
window.dispatchEvent(new Event('replacestate'));
window.dispatchEvent(new Event('locationchange'));
return ret;
};
window.addEventListener('popstate', () => {
window.dispatchEvent(new Event('locationchange'));
});
})();
Note, we're creating a closure, to save the old function as part of the new one, so that it gets called whenever the new one is called.
In modern browsers (IE8+, FF3.6+, Chrome), you can just listen to the hashchange event on window.
In some old browsers, you need a timer that continually checks location.hash. If you're using jQuery, there is a plugin that does exactly that.
Example
Below I undo any URL change, to keep just the scrolling:
<script type="text/javascript">
if (window.history) {
var myOldUrl = window.location.href;
window.addEventListener('hashchange', function(){
window.history.pushState({}, null, myOldUrl);
});
}
</script>
Note that above used history-API is available in Chrome, Safari, Firefox 4+, and Internet Explorer 10pp4+
window.onhashchange = function() {
//code
}
window.onpopstate = function() {
//code
}
or
window.addEventListener('hashchange', function() {
//code
});
window.addEventListener('popstate', function() {
//code
});
with jQuery
$(window).bind('hashchange', function() {
//code
});
$(window).bind('popstate', function() {
//code
});
EDIT after a bit of researching:
It somehow seems that I have been fooled by the documentation present on Mozilla docs. The popstate event (and its callback function onpopstate) are not triggered whenever the pushState() or replaceState() are called in code. Therefore the original answer does not apply in all cases.
However there is a way to circumvent this by monkey-patching the functions according to #alpha123:
var pushState = history.pushState;
history.pushState = function () {
pushState.apply(history, arguments);
fireEvents('pushState', arguments); // Some event-handling function
};
Original answer
Given that the title of this question is "How to detect URL change" the answer, when you want to know when the full path changes (and not just the hash anchor), is that you can listen for the popstate event:
window.onpopstate = function(event) {
console.log("location: " + document.location + ", state: " + JSON.stringify(event.state));
};
Reference for popstate in Mozilla Docs
Currently (Jan 2017) there is support for popstate from 92% of browsers worldwide.
With jquery (and a plug-in) you can do
$(window).bind('hashchange', function() {
/* things */
});
http://benalman.com/projects/jquery-hashchange-plugin/
Otherwise yes, you would have to use setInterval and check for a change in the hash event (window.location.hash)
Update! A simple draft
function hashHandler(){
this.oldHash = window.location.hash;
this.Check;
var that = this;
var detect = function(){
if(that.oldHash!=window.location.hash){
alert("HASH CHANGED - new has" + window.location.hash);
that.oldHash = window.location.hash;
}
};
this.Check = setInterval(function(){ detect() }, 100);
}
var hashDetection = new hashHandler();
Add a hash change event listener!
window.addEventListener('hashchange', function(e){console.log('hash changed')});
Or, to listen to all URL changes:
window.addEventListener('popstate', function(e){console.log('url changed')});
This is better than something like the code below because only one thing can exist in window.onhashchange and you'll possibly be overwriting someone else's code.
// Bad code example
window.onhashchange = function() {
// Code that overwrites whatever was previously in window.onhashchange
}
this solution worked for me:
function checkURLchange(){
if(window.location.href != oldURL){
alert("url changed!");
oldURL = window.location.href;
}
}
var oldURL = window.location.href;
setInterval(checkURLchange, 1000);
None of these seem to work when a link is clicked that which redirects you to a different page on the same domain. Hence, I made my own solution:
let pathname = location.pathname;
window.addEventListener("click", function() {
if (location.pathname != pathname) {
pathname = location.pathname;
// code
}
});
Edit: You can also check for the popstate event (if a user goes back a page)
window.addEventListener("popstate", function() {
// code
});
Best wishes,
Calculus
If none of the window events are working for you (as they aren't in my case), you can also use a MutationObserver that looks at the root element (non-recursively).
// capture the location at page load
let currentLocation = document.location.href;
const observer = new MutationObserver((mutationList) => {
if (currentLocation !== document.location.href) {
// location changed!
currentLocation = document.location.href;
// (do your event logic here)
}
});
observer.observe(
document.getElementById('root'),
{
childList: true,
// important for performance
subtree: false
});
This may not always be feasible, but typically, if the URL changes, the root element's contents change as well.
I have not profiled, but theoretically this has less overhead than a timer because the Observer pattern is typically implemented so that it just loops through the subscriptions when a change occurs. We only added one subscription here. The timer on the other hand would have to check very frequently in order to ensure that the event was triggered immediately after URL change.
Also, this has a good chance of being more reliable than a timer since it eliminates timing issues.
Although an old question, the Location-bar project is very useful.
var LocationBar = require("location-bar");
var locationBar = new LocationBar();
// listen to all changes to the location bar
locationBar.onChange(function (path) {
console.log("the current url is", path);
});
// listen to a specific change to location bar
// e.g. Backbone builds on top of this method to implement
// it's simple parametrized Backbone.Router
locationBar.route(/some\-regex/, function () {
// only called when the current url matches the regex
});
locationBar.start({
pushState: true
});
// update the address bar and add a new entry in browsers history
locationBar.update("/some/url?param=123");
// update the address bar but don't add the entry in history
locationBar.update("/some/url", {replace: true});
// update the address bar and call the `change` callback
locationBar.update("/some/url", {trigger: true});
To listen to url changes, see below:
window.onpopstate = function(event) {
console.log("location: " + document.location + ", state: " + JSON.stringify(event.state));
};
Use this style if you intend to stop/remove listener after some certain condition.
window.addEventListener('popstate', function(e) {
console.log('url changed')
});
The answer below comes from here(with old javascript syntax(no arrow function, support IE 10+)):
https://stackoverflow.com/a/52809105/9168962
(function() {
if (typeof window.CustomEvent === "function") return false; // If not IE
function CustomEvent(event, params) {
params = params || {bubbles: false, cancelable: false, detail: null};
var evt = document.createEvent("CustomEvent");
evt.initCustomEvent(event, params.bubbles, params.cancelable, params.detail);
return evt;
}
window.CustomEvent = CustomEvent;
})();
(function() {
history.pushState = function (f) {
return function pushState() {
var ret = f.apply(this, arguments);
window.dispatchEvent(new CustomEvent("pushState"));
window.dispatchEvent(new CustomEvent("locationchange"));
return ret;
};
}(history.pushState);
history.replaceState = function (f) {
return function replaceState() {
var ret = f.apply(this, arguments);
window.dispatchEvent(new CustomEvent("replaceState"));
window.dispatchEvent(new CustomEvent("locationchange"));
return ret;
};
}(history.replaceState);
window.addEventListener("popstate", function() {
window.dispatchEvent(new CustomEvent("locationchange"));
});
})();
While doing a little chrome extension, I faced the same problem with an additionnal problem : Sometimes, the page change but not the URL.
For instance, just go to the Facebook Homepage, and click on the 'Home' button. You will reload the page but the URL won't change (one-page app style).
99% of the time, we are developping websites so we can get those events from Frameworks like Angular, React, Vue etc..
BUT, in my case of a Chrome extension (in Vanilla JS), I had to listen to an event that will trigger for each "page change", which can generally be caught by URL changed, but sometimes it doesn't.
My homemade solution was the following :
listen(window.history.length);
var oldLength = -1;
function listen(currentLength) {
if (currentLength != oldLength) {
// Do your stuff here
}
oldLength = window.history.length;
setTimeout(function () {
listen(window.history.length);
}, 1000);
}
So basically the leoneckert solution, applied to window history, which will change when a page changes in a single page app.
Not rocket science, but cleanest solution I found, considering we are only checking an integer equality here, and not bigger objects or the whole DOM.
Found a working answer in a separate thread:
There's no one event that will always work, and monkey patching the pushState event is pretty hit or miss for most major SPAs.
So smart polling is what's worked best for me. You can add as many event types as you like, but these seem to be doing a really good job for me.
Written for TS, but easily modifiable:
const locationChangeEventType = "MY_APP-location-change";
// called on creation and every url change
export function observeUrlChanges(cb: (loc: Location) => any) {
assertLocationChangeObserver();
window.addEventListener(locationChangeEventType, () => cb(window.location));
cb(window.location);
}
function assertLocationChangeObserver() {
const state = window as any as { MY_APP_locationWatchSetup: any };
if (state.MY_APP_locationWatchSetup) { return; }
state.MY_APP_locationWatchSetup = true;
let lastHref = location.href;
["popstate", "click", "keydown", "keyup", "touchstart", "touchend"].forEach((eventType) => {
window.addEventListener(eventType, () => {
requestAnimationFrame(() => {
const currentHref = location.href;
if (currentHref !== lastHref) {
lastHref = currentHref;
window.dispatchEvent(new Event(locationChangeEventType));
}
})
})
});
}
Usage
observeUrlChanges((loc) => {
console.log(loc.href)
})
I created this event that is very similar to the hashchange event
// onurlchange-event.js v1.0.1
(() => {
const hasNativeEvent = Object.keys(window).includes('onurlchange')
if (!hasNativeEvent) {
let oldURL = location.href
setInterval(() => {
const newURL = location.href
if (oldURL === newURL) {
return
}
const urlChangeEvent = new CustomEvent('urlchange', {
detail: {
oldURL,
newURL
}
})
oldURL = newURL
dispatchEvent(urlChangeEvent)
}, 25)
addEventListener('urlchange', event => {
if (typeof(onurlchange) === 'function') {
onurlchange(event)
}
})
}
})()
Example of use:
window.onurlchange = event => {
console.log(event)
console.log(event.detail.oldURL)
console.log(event.detail.newURL)
}
addEventListener('urlchange', event => {
console.log(event)
console.log(event.detail.oldURL)
console.log(event.detail.newURL)
})
for Chrome 102+ (2022-05-24)
navigation.addEventListener("navigate", e => {
console.log(`navigate ->`,e.destination.url)
});
API references WICG/navigation-api
Look at the jQuery unload function. It handles all the things.
https://api.jquery.com/unload/
The unload event is sent to the window element when the user navigates away from the page. This could mean one of many things. The user could have clicked on a link to leave the page, or typed in a new URL in the address bar. The forward and back buttons will trigger the event. Closing the browser window will cause the event to be triggered. Even a page reload will first create an unload event.
$(window).unload(
function(event) {
alert("navigating");
}
);
window.addEventListener("beforeunload", function (e) {
// do something
}, false);
You are starting a new setInterval at each call, without cancelling the previous one - probably you only meant to have a setTimeout
Enjoy!
var previousUrl = '';
var observer = new MutationObserver(function(mutations) {
if (location.href !== previousUrl) {
previousUrl = location.href;
console.log(`URL changed to ${location.href}`);
}
});
Another simple way you can do this is by adding a click event, through a class name to the anchor tags on the page to detect when it has been clicked, then you can now use the window.location.href to get the url data which you can use to run your ajax request to the server. Simple and Easy.

How is the parameter involved in order to let function one "know" that it shall react to what happens in function two?

The following code actually works, but I don't understand why. How come that when I pass the "event"-parameter to the function zaehle(), the function actually "knows" that it is supposed to react on what happens in the setup function?
I just can't see what connnects the zaehle() and the setup() function or how the parameter that I pass to zaehle() would be involved.
I hope I could make the question clear. If not I'll gladly try to explain it somehow else. It really bugs me and I feel like I can't go on studying until I get it.
<body>
<div id="eins">0</div>
<div id="zwei">0</div>
<div id="drei">0</div>
<div id="vier">0</div>
<div id="funf">0</div>
</body>
JS
var mouseoverZaehler = 0;
function zaehle(event) {
mouseoverZaehler++;
event.target.innerHTML = mouseoverZaehler;
}
function setup() {
document.getElementById("eins").addEventListener("mouseover", zaehle);
document.getElementById("zwei").addEventListener("mouseover", zaehle);
document.getElementById("drei").addEventListener("mouseover", zaehle);
document.getElementById("vier").addEventListener("mouseover", zaehle);
document.getElementById("funf").addEventListener("mouseover", zaehle);
}
window.addEventListener("load", setup);
Here is what happens step by step:
Page loads
setup function is called (because of window.addEventListener("load", setup))
Each element in setup function gets a mouseover event listener attached to it and when it fires zaehle function is called (because of document.getElementById("number").addEventListener("mouseover", zaehle))
You move your mouse over any of the elements
zaehle function gets called - mouseoverZaehler is incremented and innerHTML of the targeted element is set to the updated value of mouseoverZaehler
Check out addEventListener docs for further details.
The addEventListener calls in your setup function tell the browser that when a mouseover event occurs on the relevant element, it should call the function you're giving it (zaehle, in your case). It's the browser that passes the argument to zaehle, later, when calling it.
You could imagine addEventListener, conceptually, as putting that handler function on a list for the event on the element:
// VERY conceptual, leaves out a lot of details
function addEventListener(eventName, handler) {
this.events[eventName].handlers.push(handler);
}
...and then later, when the event occurs, the browser creates an event object and calls those handlers:
// Again, VERY conceptual, leaves out a lot of details
var event = /*...*/;
element.events[eventName].handlers.forEach(function(handler) {
handler.call(element, event);
});
Here's a working analogue of what's going on:
function FakeElement () {
this.events = Object.create(null);
}
FakeElement.prototype.addEventListener = function(eventName, handler) {
var eventEntry = this.events[eventName];
if (!eventEntry) {
eventEntry = this.events[eventName] = {
handlers: []
};
}
eventEntry.handlers.push(handler);
};
FakeElement.prototype.trigger = function(eventName) {
var event = {type: eventName}; // "Browser" creates the event
var eventEntry = this.events[eventName];
var handlers = eventEntry && eventEntry.handlers;
if (handlers) {
handlers.forEach(function(handler) {
handler.call(this, event); // "Browser" calls handler, passing
}); // the event into it
}
};
// Using it:
function zaehle(event) {
console.log("zaehle got event: " + event.type);
}
var e = new FakeElement();
e.addEventListener("mouseover", zaehle);
console.log("added handler for mouseover to element");
// Simulate the event occurring
var timer = setInterval(function() {
e.trigger("mouseover");
}, 500);
setTimeout(function() {
clearInterval(timer);
}, 3000);
You have registered your callback/function zaehle() for mouseover event. So when that event occurs for a specific div, browser calls the callback with event object which contains information about the event and the target i.e event occurred on which element.

Define the order of execution of functions after event in javascript

Just, before reading, I have read about this thread: Order of execution of functions bound to an event in Javascript but its not helping. Actually,
I have an anonymous function, define like that:
<input type="button" name="blablabla" value="Send" onclick="javascript:blablabla">
So, this function is on a button, use to validate forms. As you can see, It's an anonymous function, and I don't have any access on this code. This function start when I click on it. Okay, I have understood that
But, this function is not totally full, and I want to add my own, with her own logic of check. So I want my checks first, and then call the anonymous function. Here is my code:
function check() {
console.log("debut de check");
var participant = document.getElementById("new_participant_name");
var participant1 = document.getElementById("new_participant2_name");
var participant2 = document.getElementById("new_participant3_name");
participant = participant.value;
participant1 = participant1.value;
participant2 = participant2.value;
var trois_participants = (participant2) ? true : false;
if (!participant1 || !participant)
{
console.log("pas de participant1 ou participant, sert à rien de gérer la suite");
//if the script come here, I want to stop processing, and don't want to call the anonymous function.
return ;
}
}
window.onload = function()
{
document.getElementById("InsertButton").addEventListener('click', function () {
check();
})};
So, I want to call my function (check) before the anonymous function, but, with the same event. I don't know if I am totally understable... thanks per avance
EDIT: Sorry guys, My code have a bug before, yes the code is inlined, I will try all of your solutions tomorrow, thanks guys
If (and only if) the existing handler is attached using an inline onclick="..." handler, you can obtain its value, and then overwrite it:
window.onload = function() {
var el = document.getElementById('InsertButton');
var old_click = el.onclick;
el.onclick = undefined;
el.addEventListener('click', function() {
check();
old_click(this);
});
}
Why not create your own handler??
Element.prototype.myEventListener=function(name,func){
this.addEventListener(name,function(){
if(!check()){return;}
func();
});
};
Now you can do:
document.body.myEventListener("click",function(){
alert("t");
});
Check will always be called before the registered handler.
Note, to block the call, check must return false:
function check(){
return false;//no custom eventlistener fires
return true;//all will fire
}
Use the useCapture flag so you can intercept the event while it's travelling down to the button.
At that point you can perform your check, and if it fails you can call stopPropagation on the event to prevent it from reaching the handlers that are attached to its bubbling phase.
Also, by nature, events are quite bad at managing the order of execution. In general they depend on the order of registration of the listeners.
// code over which you have no control and can't change
var btn = document.getElementById("greeter");
btn.addEventListener("click", function() {
console.log("hello");
})
// code you can add later
function check() {
return Math.random() > 0.5;
}
window.addEventListener("click", function(e) {
var greeter = document.getElementById("greeter");
if (e.target === greeter && !check()) {
e.stopPropagation();
}
}, true)
<button id="greeter">hello world</button>

How to show the result of this jQuery function without the need of clicking the button?

I have this function below, however I want to make it work on windows load and show the result without clicking the button.
This is the code I use https://raw.githubusercontent.com/SuyashMShepHertz/indexedDB_sample/master/index.html
How to do this?
$("#getBtn").click(function(){
var type = 'permanent';
var request = db.transaction(["hashes"],"readwrite").objectStore("hashes").get(type);
request.onsuccess = function(event){
$("#result").html("Name : "+request.result.name);
};
});
just put your code in
$( window ).load(function() {
//Code Here
});
If you need it both on click and initially when the page loads, make it a reusable function:
function doTheThing() {
var type = 'permanent';
var request = db.transaction(["hashes"], "readwrite").objectStore("hashes").get(type);
request.onsuccess = function(event) {
$("#result").html("Name : " + request.result.name);
};
}
Then call it from both places you need it:
On page load
On click
To call it on page load, just make sure your script is at the end of the HTML (just before the closing </body> tag; this is best practice unless you have a good reason for doing something else) and call it:
doTheThing();
If you can't put the script at the end of the HTML, you can use jQuery's ready callback instead:
// Concise, but easy to misunderstand:
$(doTheThing);
// Or more verbose but also more clear:
$(document).ready(doTheThing);
(See note below about doing it directly or indirectly.)
To call it on click, hook it up, either directly or indirectly:
// Directly
$("#getBtn").click(doTheThing);
// Or indirectly
$("#getBtn").click(function() {
doTheThing();
});
The only reason for hooking it up indirectly would be to avoid having it receive the event object jQuery will pass it automatically, and to avoid having its return value examined by jQuery to see if it should stop propagation and prevent the default event action.
To avoid creating globals, I'd make sure the entire thing is in a scoping function:
(function() {
function doTheThing() {
var type = 'permanent';
var request = db.transaction(["hashes"], "readwrite").objectStore("hashes").get(type);
request.onsuccess = function(event) {
$("#result").html("Name : " + request.result.name);
};
}
doTheThing();
$("#getBtn").click(doTheThing);
})();
just put it in $(document).ready, like this
$(document).ready(function(){
var type = 'permanent';
var request = db.transaction(["hashes"],"readwrite").objectStore("hashes").get(type);
request.onsuccess = function(event){
$("#result").html("Name : "+request.result.name);
};
});

How to "scope" event listeners?

This is my code:
var myFunction(){
document.addEventListener("deviceready", self.onDeviceReady, false); // scoped event listener
function onDeviceReady() {
// ...
}
}
As far as I see when the event (deviceready) is triggered, the local (to myFunction) callback is run.
However the event listeners is global so another function with the same with global scope may be called as well, once the event is triggered.
How to make not only the callback, but the listener itself locally scoped to a function (I know how to do it for a DOM element but that's different)?
Elements themselves are scoped globally. As soon as you attach something to them, they are scoped that way. Consider the following ::
function myfunc(){
document.getElementById('someId').something = 'test';
}
This will now be accessed everywhere.
I see what you want to get at so you could try several things. Here is something you could try. This will check to see if an event already exists for an element and not let you add another.
var Marvel = {
on : function(element, action, callback){
Marvel.listeners = Marvel.listeners || {};
Marvel.listeners[action] = Marvel.listeners[action] || [];
for(var index in Marvel.listeners[action]){
if(Marvel.listeners[action][index].element == element){
return console.error("A '"+action+"' event is already established for:", element, Marvel.listeners[action][index]), false
}
}
element.addEventListener(action,callback);
Marvel.listeners[action].push({ element: element, callback: callback });
},
off: function(element, action){
if(!Marvel.listeners || !Marvel.listeners[action])
return console.error("off: No '"+action+"' listener has been created. Listeners: ", Marvel.listeners || 'none'), false;
for(var index in Marvel.listeners[action]){
if(Marvel.listeners[action][index].element == element){
element.removeEventListener(action, Marvel.listeners[action][index].callback);
Marvel.listeners[action].splice(index, 1);
return true
}
}
return console.error("A '"+action+"' event has not yet been established for:", element, Marvel.listeners[action]), false;
}
}
Usage:
Marvel.on(document, click, function(e){
console.log(e.target);
});
Marvel.off(document, click);
This sets an event listener to be stored in a separate object and checks to see if it already exists when adding new ones, and additionally allows the capability to have an off function to turn them off.
You can find the full explanation for this on my site in my profile in the Javascript Tracking Events section.
Your code should be like this :
function myFunction() {
document.addEventListener("deviceready", function () {
//...
}, false); // scoped event listener
}

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