I dont know a whole lot about javascript and i was wondering if this script would run or do i need to put the "if statement" inside some kind of onPageLoad function to run this? Please help.
<script>
if (time<20)
{
alert("Hello World!");
}
</script>
Sure it would run -- but it would depend on something else having run first so that time has a value.
For example, this would work (even though it's bad practice because it sets a property on window):
<script>
time = 10;
</script>
<script>
if (time<20)
{
alert("Hello World!");
}
</script>
You would also find it impossible to guarantee that any variables you need for temporary processing are kept out of the reach of other scripts. To overcome this limitation, you can (and except in the most trivial of sites, should) wrap the code inside an anonymous function that is invoked on the spot:
<script>
(function() {
// your code here
})();
</script>
If you want to access DOM Elements you have to put the script tag at the end of the page. Or you use something like onload of the body tag (or an equivalent funciton in JS framework)
It would run, realize time is undefined, generate an error and halt operations from that point on.
If "time" is seted on server side, so, you may write onload property body dinamically like this:
<body onload="functionName(<?php echo()?>)">
and then:
<script type="text/javascript">
function functionName(time) {
if(time < 30) { ... }
}
</script>
Related
I want to execute a piece of C# code whenever I run a JavaScript function but it doesn't seem to behave the way I want it to here is an example:
Let's say that I have a variable property int Counter {get; set; } in the Model that I want to increment every time I run a JavaScript function:
<script type="text/javascript">
function MyFunction(){
//Do some stuff
#{Model.Counter++;}
}
</script>
What is really happening is that when the page loads #{Model.Counter++;} is getting executed regardless of not being called from the function.
And whenever I run the function again its ignoring it completely.
Meaning this piece of code #{Model.Counter++;} is getting executed once when the page loads and never again.
How do I fix that and make it execute every time I run the function?
You can use ActiveX control to execute Compiled program. but you should know that your html code only will work in IE.
You will have to create a hidden field for model.counter somewhere inside a view form
<input type="hidden" id="modelCounter" asp-for="Counter" value="#Model.Counter" />
after this you can change Counter using javascript
function MyFunction(){
//Do some stuff
var counter=$("#modelCounter").val();
counter++;
$("#modelCounter").val(counter);
}
I don't think what you want is possible (maybe with Blazor? - but that is WebAssembly).
Instead you can assign a new javascript variable to your model property.
E.g.:
<script type="text/javascript">
function MyFunction(){
//Do some stuff
let counter = #{Model.Counter};
counter++;
// Do some stuff with counter
}
// When you are done, post the counter back if needed on server side
</script>
Try This
#{
var a=Model.Counter;
}
do this outside the script
and inside the function or script
do
#a++;
or
var c = #a;
c++;
hope it works
I have a web element that only appears while the page (or a part of the page) is still loading and disappears when the page has been completely loaded. I would like to see precisely when this element disappears and I can do that by repeatedly running something like that in the browser console:
$("div.v-app-loading")
or alternatively:
document.getElementsByClassName('v-app-loading')
But in most cases everything happens too fast and I am unable to catch the exact moment. There must be a way to create a loop that will just run in the console and execute one of the commands I mentioned say every 0.5sec or even more frequently.
Could anyone point me to the right direction?
You can use Javascript's setInterval() as following:
function yourFunction(){
//do something here...
}
setInterval(yourFunction, 500); //Will run the function every half a second(500ms = 0.5s)
Maybe it's easier to use jQuery to detect when the page is loaded:
HTML
<body class="loading">
JS
// do something initially here
$(window).load(function () {
// do something when finished loading
$('body').removeClass('loading');
});
Edit: If you rather wanted to check for existence of an elemtent, do it in a recursive function call. You can throttle it with setTimeout, but you don't need to:
function checkElement() {
if ($('.v-app-loading').length) {
checkElement();
// or: setTimeout(checkElement, 100);
} else {
// Element disappeared
}
}
checkElement();
How can I unload a JavaScript resource with all its defined objects from the DOM?
Im developing a simple framework that enables to load html fragments into a "main" html. Each fragment is self contained and may include references to additional JS and CSS files. The JS and CSS resources are parsed and dynamically added to the html. When the fragment is removed/replaced from the DOM I want to remove its JS and CSS.
If I remove the script element in the example below, the functions defined in page1.js are still available.
<html>
<head>
<script src="page1.js" type="text/javascript"></script>
</head>
<body>
...
Is there a way to unload page1.js objects from the DOM?
========= The test code I use =======
I tried the advice i got in the comments below; to delete the added objects using a cleanup function - but even this fails. The sources i used for testing:
<html>
<head>
<script type="text/javascript">
function loadJSFile(){
var scriptTag = document.createElement("script");
scriptTag.setAttribute("type", "text/javascript");
scriptTag.setAttribute("src", "simple.js");
var head = document.getElementsByTagName("head")[0];
head.appendChild(scriptTag);
}
function unloadJSFile(){
delete window.foo;
delete window.cleanup;
alert("cleanedup. typeof window.foo is " + (typeof window.foo));
}
</script>
</head>
<body>
Hello JavaScript Delete
<br/>
<button onclick="loadJSFile();">Click to load JS</button>
<br/>
<button onclick="foo();">call foo()</button>
<br/>
<button onclick="unloadJSFile();">Click to unload JS</button>
</body>
</html>
simple.js source:
var foo = function(){
alert("hello from foo");
}
This cannot be done.
When a script is executed, function definitions are added to the global window object. There may be debugging symbols attached to the function that indicate where the function came from, but this information is not available to scripts.
About the only way you could achieve something like this would be to create a pseudo-namespace in the script and then throw away that whole namespace when you are done with it. However, this question hints to me that you are trying to do something the wrong way. Perhaps elaborating on your scenario would help us provide alternate solutions.
No, that is not possible. You could build a simple cleanup function that removes all variables that were defined in that file:
var foo = 'bar';
var cleanup = function () {
delete window.foo;
delete window.cleanup;
};
// unload all resources
cleanup();
Another approach would be to use a modular object structure for your fragments, that clean up after themselves. That involves a slightly higher overhead but is probably worth it, as it makes the code much easier to read and maintain:
// creates the object using the second parameter as prototype.
// .create() is used as constructor
GlobalModuleHandlerThingy.addModule('my_module', {
create: function () {
this.foo = 'bar';
return this;
},
foo: null,
destroy: function () {
// unload events, etc.
}
});
GlobalModuleHandlerThingy.getModule('my_module').foo; // => bar
GlobalModuleHandlerThingy.unloadModule('my_module'); // calls .destroy() on the module and removes it.
perhaps you need to consider conditionally loading it rather than conditionally unloading it...
you can make them = null
function fnc1 (){
}
window.fnc1 = null
//or
window["fnc1"] = null
If you need to unload a specific object, it's fairly easy: just set it to {}
ie: myobj = {};
So if you know what objects are created in a particular include, it won't be hard at all.
On the other hand, if you don't know what objects are created in a particular include, there isn't a mechansim to find out - you can't ask Javascript to tell you what was defined in a particular include.
However, I would say that if you don't know what objects are being loaded in a particular javascript file, you're probably not doing yourself any favours in loading it (you should always have a reasonable idea what code does in your site), or in trying to unload it manually (if you don't know what it does, that implies its a third party include, which means that unsetting it manually is likely to break things).
Was researching for something like that myself and thought I'll post my findings
Wrap your stuff in a global namespace in js file so it can be removed easily, ie
var stuff = { blabla: 1, method: function(){} };
When you need to get rid of it, simply set stuff = {}, or null even
Remove script tag from page
*** If you use requirejs - require js remove definition to force reload
Note: as long as you don't reference modules inside the namespace from anywhere else everything will be collected by GC and you are good to go.
I figured a trick for this. I was wondering here days finding an answer for this and I just realized a perfect trick to do this without trying to unload the java Script. only you have to do is create a global variable like currentPage in your main page's java script and when you loading the page assign the page name to currentPage . then in every other .js file use $('document').ajaxComplete() insted of $('document').ready() add an if statement as first line inside every $('document').ajaxComplete() function. set it to check currentPage variable equals to a new page name. add all other events inside if statement. i don't know English very well so check my code. and This is my first answer here so sorry if i make some mistakes.
main.html
<body>
<div id='container></div>
<button id="load1">
<button id="load1">
</body>
main.js
var currentPage = "";
$(document).ready(function () {
$('#load1').click(function () {
loadSource('page1', 'body');
});
$('#load2').click(function () {
loadSource('page2', 'body');
});
});
function loadSource( page, element){
currentPage = page;
$('#container').load('views/' + page + '.php', element);
$.getScript('js/' + page + '.js');
$('#css').prop('disabled', true).remove();
$('head').append('<link rel="stylesheet" href="css/' + page + '.css" type="text/css" />');
}
all of my pages scripts and styles are in seperate folders views, js, css.
page1.html
<body>
<button id="test1">
<button id="test2">
</body>
page1.js
$(document).ajaxComplete(function () {
if(currentPage == 'page1'){
/*$('#test1').click(function () {
console.log('page1');
});*/
$('#test2').click(function () {
console.log('page1');
});
}
});
page2.html
<body>
<button id="test1">
<button id="test2">
</body>
page2.js
$(document).ajaxComplete(function () {
if(currentPage == 'page2'){
$('#test1').click(function () {
console.log('page2');
});
/*$('#test2').click(function () {
console.log('page2');
});*/
}
});
i commented one button in each script to check if that button still has old script's affect.
Not sure the best way to phrase the question, but suppose you are using jQuery to setup various things like so:
<script>
function doSecond(){
alert("Hi");
}
function dofirst(){
var x = asdasd;
}
$(dofirst);
$(doSecond);
</script>
So, imagine that dofirst and dosecond are completely independent. If dofirst throws an exception, which of course it will, then doSecond will never fire. I understand why this happens, but I'm wondering if there is a way of getting around this without having to wrap EVERY kind of jQuery handler that I want to set up in a try catch. E.g., I'd rather not do:
try{
$(doFirst);
}
catch{
//maybe log here?
}
try{
$(doSecond);
}
catch{
//maybe log here?
}
Now, if you're wondering why I want to do this? Well, take for example the code on the page you're looking at right now:
<script type="text/javascript">
$(function() {
$('#title').focus(function() { $('#how-to-tag').hide(); $('#how-to-format').hide(); $('#how-to-title').fadeIn('slow'); });
$('#wmd-input').focus(function() { $('#how-to-tag').hide(); $('#how-to-format').fadeIn('slow'); $('#how-to-title').hide(); });
$('#tagnames').focus(function() { $('#how-to-tag').fadeIn('slow'); $('#how-to-format').hide(); $('#how-to-title').hide(); });
});
</script>
Is it really necessary to have certain dom elements fade out when you click on them? No. But if you make a mistake in that function, then quite possibly other javascript that you really, really do need to run may never get setup.
A couple of ways to ensure things run independently of each other:
As you said, try/catch around each
Call each in a setTimeout (or
whatever the jQuery syntactic sugar
is for that)
Separate into different <script>
blocks
Obviously not ever throwing an exception is a ridiculous suggestion. Especially in the world of many browsers/versions/servers up/servers down. There are so many ways of website JS to break it's hard to find a site of any size which doesn't throw an exception of some type (on console examination).
You could create a simple wrapper (or extend existing jQuery methods)
function safeonload(fn){
$(function(){
try{
fn();
}catch{
//log?
}
});
}
safeonload(doFirst);
safeonload(doSecond);
Is there an event that fires when JavaScript files are loaded? The problem came up because YSlow recommends to move JavaScript files to the bottom of the page. This means that
$(document).ready(function1) is fired before the js file that contains the code for function1 is loaded.
How to avoid this kind of situation?
I don't have a reference for it handy, but script tags are processed in order, and so if you put your $(document).ready(function1) in a script tag after the script tags that define function1, etc., you should be good to go.
<script type='text/javascript' src='...'></script>
<script type='text/javascript' src='...'></script>
<script type='text/javascript'>
$(document).ready(function1);
</script>
Of course, another approach would be to ensure that you're using only one script tag, in total, by combining files as part of your build process. (Unless you're loading the other ones from a CDN somewhere.) That will also help improve the perceived speed of your page.
EDIT: Just realized that I didn't actually answer your question: I don't think there's a cross-browser event that's fired, no. There is if you work hard enough, see below. You can test for symbols and use setTimeout to reschedule:
<script type='text/javascript'>
function fireWhenReady() {
if (typeof function1 != 'undefined') {
function1();
}
else {
setTimeout(fireWhenReady, 100);
}
}
$(document).ready(fireWhenReady);
</script>
...but you shouldn't have to do that if you get your script tag order correct.
Update: You can get load notifications for script elements you add to the page dynamically if you like. To get broad browser support, you have to do two different things, but as a combined technique this works:
function loadScript(path, callback) {
var done = false;
var scr = document.createElement('script');
scr.onload = handleLoad;
scr.onreadystatechange = handleReadyStateChange;
scr.onerror = handleError;
scr.src = path;
document.body.appendChild(scr);
function handleLoad() {
if (!done) {
done = true;
callback(path, "ok");
}
}
function handleReadyStateChange() {
var state;
if (!done) {
state = scr.readyState;
if (state === "complete") {
handleLoad();
}
}
}
function handleError() {
if (!done) {
done = true;
callback(path, "error");
}
}
}
In my experience, error notification (onerror) is not 100% cross-browser reliable. Also note that some browsers will do both mechanisms, hence the done variable to avoid duplicate notifications.
When they say "The bottom of the page" they don't literally mean the bottom: they mean just before the closing </body> tag. Place your scripts there and they will be loaded before the DOMReady event; place them afterwards and the DOM will be ready before they are loaded (because it's complete when the closing </html> tag is parsed), which as you have found will not work.
If you're wondering how I know that this is what they mean: I have worked at Yahoo! and we put our scripts just before the </body> tag :-)
EDIT: also, see T.J. Crowder's reply and make sure you have things in the correct order.
Take a look at jQuery's .load() http://api.jquery.com/load-event/
$('script').load(function () { });
Further to #T.J. Crowder 's answer, I've added a recursive outer loop that allows one to iterate through all the scripts in an array and then execute a function once all the scripts are loaded:
loadList([array of scripts], 0, function(){// do your post-scriptload stuff})
function loadList(list, i, callback)
{
{
loadScript(list[i], function()
{
if(i < list.length-1)
{
loadList(list, i+1, callback);
}
else
{
callback();
}
})
}
}
Of course you can make a wrapper to get rid of the '0' if you like:
function prettyLoadList(list, callback)
{
loadList(list, 0, callback);
}
Nice work #T.J. Crowder - I was cringing at the 'just add a couple seconds delay before running the callback' I saw in other threads.
I always make a call from the end of the JavaScript files for registering its loading and it used to work perfect for me for all the browsers.
Ex: I have an index.htm, Js1.js and Js2.js. I add the function IAmReady(Id) in index.htm header and call it with parameters 1 and 2 from the end of the files, Js1 and Js2 respectively. The IAmReady function will have a logic to run the boot code once it gets two calls (storing the the number of calls in a static/global variable) from the two js files.
Change the loading order of your scripts so that function1 was defined before using it in ready callback.
Plus I always found it better to define ready callback as an anonymous method then named one.
Like T.J. wrote: the order is defined (at least it's sequential when your browser is about to execute any JavaScript, even if it may download the scripts in parallel somehow). However, as apparently you're having trouble, maybe you're using third-party JavaScript libraries that yield some 404 Not Found or timeout? If so, then read Best way to use Google’s hosted jQuery, but fall back to my hosted library on Google fail.