I want to access variable from iframe without editing iframeContent.html page. I don't know why alert window still shows 'undefined'
<!DOCTYPE html>
<html>
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<script type="text/javascript">
var iframe0=0;
var iframe0document=0;
var inputIframe=0;
function getIframeText() {
var iframe0 = document.getElementById("iframe123");
var iframe0document=iframe0.contentDocument||iframe0.contentWindow.document;
var inputIframe = iframe0document.getElementById("wynik2");
alert(inputIframe.value);
};
</script>
</head>
<body>
<div>
<button onclick="getIframeText()">get iframe text</button>
<iframe id="iframe123" src="iframeContent.html" >
</div>
</body>
</html>
iframeContent.html:
<html>
<head>
<title>IFrame Child Example</title>
<script type="text/javascript">
var asd="12";
</script>
</head>
<body>
<div id="wynik2"></div>
<script type="text/javascript">
document.getElementById("wynik2").innerHTML=asd;
</script>
</body>
</html>
Frame on parent page looks good (shows number 12). I'm testing my page on Chrome but through command window typing 'allow file access from files'. So this isn't problem. Global variables are also set (am I doing it right?) so I don't know why is still udefined.
use inputIframe.innerText instead of inputIframe.value . "wynik2" is a div, right? cheers! :)
I'm trying to load bootstrap.min.js file.
I have two options.
The first one is to load it from a remote server:
<!DOCTYPE html>
<html lang='ru'>
<head>
<meta charset='utf-8'>
<script src="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/js/bootstrap.min.js"></script>
</head>
<body>
...
</body>
</html>
The second one is to load it from my server:
<!DOCTYPE html>
<html lang='ru'>
<head>
<meta charset='utf-8'>
<script src="js/bootstrap.min.js"></script>
</head>
<body>
...
</body>
</html>
In the first case the script will load asynchronously which means the rendering of my page won't be blocked.
In the second case the script will block the rendering of my page. Am I correct?
How will blootstrap.min.js be loaded (async or sync) if I try to do this :
<!DOCTYPE html>
<html lang='ru'>
<head>
</head>
<body>
<script>
var bootstrap = document.createElement('script');
bootstrap.src = "http://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/js/bootstrap.min.js";
var head = document.getElementsByTagName('head')[0];
head.appendChild(bootstrap);
</script>
...
</body>
</html>
And this:
<!DOCTYPE html>
<html lang='ru'>
<head>
</head>
<body>
<script>
var bootstrap = document.createElement('script');
bootstrap.src = "js/bootstrap.min.js";
var head = document.getElementsByTagName('head')[0];
head.appendChild(bootstrap);
</script>
...
</body>
</html>
I have a hunch that in both cases the rendering won't be blocked. What do you think? Thanks!
If you put the source-loading code at the end of your <body> tag, the rendering won't be blocked, even though the new script tags are appended to the head. That's because most of the rendering is already done when you get to that part.
In newer browsers, you can add an async attribute to the script tag, which will not block rendering. So I suspect loading the file asynchronously via JS will not block rendering either, even if you do it near the top of the file.
I'm trying to create a redirect page but I need to use two parameters to create the address link.
<!DOCTYPE html>
<!--
Test file
-->
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<!--<meta http-equiv="refresh" content="0;url=link" />-->
</head>
<body>
<p>Redirecting...</p>
<script language="javascript">
var chapterx = document.getElementById("chapter").value;
var linex = document.getElementById("line").value;
var link = "http://www.mypage.com/help?chapter=" + chapterx + "," + linex;
//window.prompt(link);
window.location = link;
</script>
</body>
</html>
I'm testing this by loading the page from my PC, not from the server.
I have very basic concept about HTML and JS and I can't figure out what I'm doing wrong.
I read something from Redirect from an HTML page to create that code.
Plus, theres any way to write the 'link' variable before redirect to see what happen?
Also I have Firebug installed but I cant found the variables that I declared to see their status.
Your code is correct. But it will not work because JavaScript detects an error on that line:
var chapterx = document.getElementById("chapter").value;
You don't have any element on your page with the chapter id. Your next line is erroneous too because there is no element on your page with the line id.
I added this to your code:
<div id="chapter"></div>
<div id="line"></div>
after <p>Redirecting...</p> and it successfully redirected me to:
http://www.mypage.com/help?chapter=undefined,undefined
Hopefully that helped?:)
Reading the link posted by Lucio I make the following code
<!DOCTYPE html>
<!--
Test file
-->
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<!--<meta http-equiv="refresh" content="0;url=link" />-->
</head>
<body>
<p>Redirecting...</p>
<script language="javascript">
var chapterx = decodeURIComponent(window.location.search.match(/(\?|&)chap\=([^&]*)/)[2]);
var linex = decodeURIComponent(window.location.search.match(/(\?|&)lin\=([^&]*)/)[2]);
var link = "http://www.myweb.com/help.html?chapter=" + chapterx + "," + linex;
window.location = link;
</script>
</body>
</html>
This is my site: http://vani.valse.com.my/pixel
I tested in https://developers.google.com/speed/pagespeed/insights.
It asks to remove render blocking js file which is "js/jquery-1.7.1.min.js".
But I don't have this file anywhere in my site and all js files are compressed and placed at the footer.
I even defer the page from loading but nothing works. Below is my defer code:
<script type="text/javascript">
function downloadJSAtOnload() {
var element = document.createElement("script");
element.src = "js/jquery-1.7.1.min.js";
document.body.appendChild(element);
}
if (window.addEventListener)
window.addEventListener("load", downloadJSAtOnload, false);
else if (window.attachEvent)
window.attachEvent("onload", downloadJSAtOnload);
else window.onload = downloadJSAtOnload;
</script>
Can anyone advise why does the error shown even when the file is nowhere to be found?Many thanks.
HTML (index.php)
<!doctype html>
<html class="no-js" lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width,initial-scale=1">
<title>Pixel Marketing - Home</title>
<link rel="stylesheet" href="css/foundation.min.css">
</head>
<body id="home">
<div class="row collapse">
<div class="menu">
<?php
include('inc/menu.php');
?>
</div>
</div>
<!--content here-->
<script src="js/foundation.min.js"></script>
<script>
$(document).foundation();
</script>
</body>
</html>
It seems path not provided correctly in
element.src = "js/jquery-1.7.1.min.js";
Either you write the path correctly
element.src = "full-path-to-jquery/jquery-1.7.1.min.js";
you can pull it from CDN
element.src = "https://code.jquery.com/jquery-1.7.1.min.js";
It's best practice to include all the scripts at the end of the page, just right before closing the body tag. This is because when the browser finds a script tag, it downloads and executes it before continuing reading the page, hence "blocking" the page from loading.
You are actually including jquery near the top of the page:
<script src="js/jquery-1.7.1.min.js" type="text/javascript"></script>
And it does give an error in the console when loading the page because yes, you don't have that file. Remove it and the script right after it if you don't need it, and you should be fine.
Why do I get an error or Uncaught TypeError: Cannot set property 'innerHTML' of null?
I thought I understood innerHTML and had it working before.
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Untitled Document</title>
<script type ="text/javascript">
what();
function what(){
document.getElementById('hello').innerHTML = 'hi';
};
</script>
</head>
<body>
<div id="hello"></div>
</body>
</html>
You have to place the hello div before the script, so that it exists when the script is loaded.
Let us first try to understand the root cause as to why it is happening in first place.
Why do I get an error or Uncaught TypeError: Cannot set property
'innerHTML' of null?
The browser always loads the entire HTML DOM from top to bottom. Any JavaScript code written inside the script tags (present in head section of your HTML file) gets executed by the browser rendering engine even before your whole DOM (various HTML element tags present within body tag) is loaded. The scripts present in head tag are trying to access an element having id hello even before it has actually been rendered in the DOM. So obviously, JavaScript failed to see the element and hence you end up seeing the null reference error.
How can you make it work as before?
You want to show the hi message on the page as soon as the user lands on your page for the first time. So you need to hook up your code at a point when you are completely sure of the fact that DOM is fully loaded and the hello id element is accessible/available. It is achievable in two ways:
Reorder your scripts: This way your scripts get fired only after the DOM containing your hello id element is already loaded. You can achieve it by simply moving the script tag after all the DOM elements i.e. at the bottom where body tag is ending. Since rendering happens from top to bottom so your scripts get executed in the end and you face no error.
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Untitled Document</title>
</head>
<body>
<div id="hello"></div>
<script type ="text/javascript">
what();
function what(){
document.getElementById('hello').innerHTML = 'hi';
};
</script>
</body>
</html>
Use event hooking: Browser's rendering engine provides an event based hook through window.onload event which gives you the hint that browser has finished loading the DOM. So by the time when this event gets fired, you can be rest assured that your element with id hello already loaded in the DOM and any JavaScript fired thereafter which tries to access this element will not fail. So you do something like below code snippet. Please note that in this case, your script works even though it is present at the top of your HTML document inside the head tag.
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Untitled Document</title>
<script type ="text/javascript">
window.onload = function() {
what();
function what(){
document.getElementById('hello').innerHTML = 'hi';
};
}
</script>
</head>
<body>
<div id="hello"></div>
</body>
</html>
You could tell javascript to perform the action "onload"... Try with this:
<script type ="text/javascript">
window.onload = function what(){
document.getElementById('hello').innerHTML = 'hi';
};
</script>
Just put your JS in window.onload
window.onload = function() {
what();
function what() {
document.getElementById('hello').innerHTML = 'hi';
};
}
The JavaScript part needs to run once the page is loaded, therefore it is advised to place JavaScript script at the end of the body tag.
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Example</title>
</head>
<body>
<div id="hello"></div>
<script type ="text/javascript">
what();
function what(){
document.getElementById('hello').innerHTML = 'hi';
};
</script>
</body>
</html>
Javascript looks good. Try to run it after the the div has loaded. Try to run only when the document is ready. $(document).ready in jquery.
Here Is my snippet try it. I hope it will helpfull for u.
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Untitled Document</title>
</head>
<body>
<div id="hello"></div>
<script type ="text/javascript">
what();
function what(){
document.getElementById('hello').innerHTML = 'hi';
};
</script>
</body>
</html>
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Example</title>
</head>
<body>
<div id="hello"></div>
<script type ="text/javascript">
what();
function what(){
document.getElementById('hello').innerHTML = '<p>hi</p>';
};
</script>
</body>
</html>
You could try using the setTimeout method to make sure your html loads first.
The root cause is: HTML on a page have to loaded before javascript code.
Resolving in 2 ways:
1) Allow HTML load before the js code.
<script type ="text/javascript">
window.onload = function what(){
document.getElementById('hello').innerHTML = 'hi';
}
</script>
//or set time out like this:
<script type ="text/javascript">
setTimeout(function(){
what();
function what(){
document.getElementById('hello').innerHTML = 'hi';
};
}, 50);
//NOTE: 50 is milisecond.
</script>
2) Move js code under HTML code
<div id="hello"></div>
<script type ="text/javascript">
what();
function what(){
document.getElementById('hello').innerHTML = 'hi';
};
</script>
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Untitled Document</title>
</head>
<body>
<div id="hello"></div>
<script type ="text/javascript">
what();
function what(){
document.getElementById('hello').innerHTML = 'hi';
};
</script>
</body>
</html>
I have had the same problem and it turns out that the null error was because I had not saved the html I was working with.
If the element referred to has not been saved once the page is loaded is 'null', because the document does not contain it at the time of load. Using window.onload also helps debugging.
I hope this was useful to you.
This error can appear even if you load your script after the html render is finished. In this given example your code
<div id="hello"></div>
has no value inside the div. So the error is raised, because there is no value to change inside. It should have been
<div id="hello">Some random text to change</div>
then.
Add jquery into < head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.0/jquery.min.js"></script>
Use $document.ready() : the code can be in < head> or in a separate file like main.js
1) using js in same file (add this in the < head>):
<script>
$( document ).ready(function() {
function what(){
document.getElementById('hello').innerHTML = 'hi';
};
});
</script>
2) using some other file like main.js (add this in the < head>):
<script type="text/javascript" src="/path/to/main.js" charset="utf-8"></script>
and add the code in main.js file :)
You need to change div into p. Technically innerHTML means it is inside the <??? id=""></???> part.
Change:
<div id="hello"></div>
into
<p id="hello"></p>
Doing:
document.getElementById('hello').innerHTML = 'hi';
will turn
<div id="hello"></div> into this <div id="hello">hi</div>
which actually does not make sense.
You can also try to change:
document.getElementById('hello').innerHTML = 'hi';
into this
document.getElementById('hello').innerHTML='<p> hi </p> ';
to make it work.
The error is self-explaining it is not getting the HTML tag in which You want to set the Data So make tag available to JS then only You can set Data to that.
No doubt, most of the answers here are correct, but you can also do this:
document.addEventListener('DOMContentLoaded', function what() {
document.getElementById('hello').innerHTML = 'hi';
});
There are different possible cause as discussed would just like to add this for someone who might have the same issue as mine.
In my case I had a missing close div as shown below
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Untitled Document</title>
</head>
<body>
<div> //I am an open div
<div id="hello"></div>
<script type ="text/javascript">
what();
function what(){
document.getElementById('hello').innerHTML = 'hi';
};
</script>
</body>
</html>
Missing a close div can result in disorganization of the transversal from child to parent or parent to child hence resulting in an error when you try to access an element in the DOM
Let the DOM load. To do something in the DOM you have to Load it first. In your case You have to load the <div> tag first. then you have something to modify. if you load the js first then that function is looking your HTML to do what you asked to do, but when that time your HTML is loading and your function cant find the HTML. So you can put the script in the bottom of the page. inside <body> tag then the function can access the <div> Because DOM is already loaded the time you hit the script.
I have moved my <script> tag below the <body> tag. Let’s try
<body>
<p>The time is <span id="time"></span>.</p>
</body>
<script>
// Allways keep script at end for date and time object //
var d = new Date();
document.getElementById("time").innerHTML = d;
</script>
This happened to me when using Django template tags on an if-check to see if there was a value available for a field - if no value I removed everything associated with the value from the page to keep things neat The only problem was the content I removed included the div and id I was trying to work with! If there was a value present there was no issue as the div that contained the id I was working with was present. If there was no value I received the error. Once it hit me that's what was going on then easy fix to just add the div in there if the if-check is false.
Before
{% if model.value %}
<div id='my-id'>{{model.value}}</div>
{% endif %}
After
{% if model.value %}
<div>{{model.value}}</div>
{% else %}
<div id='my-id'></div>
{% endif %}