问题
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>
回答1:
You have to place the hello div before the script, so that it exists when the script is loaded.
回答2:
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>
回答3:
I see that all the techies have provided the solution on how to get rid of the problem but nobody has catered to the reason or 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
helloid element is already loaded. You can achieve it by simply moving the script tag after all the DOM elements i.e. at the bottom wherebodytag 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>- Using event hooking: Browser's rendering engine provides an event based hook through
window.onloadevent 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 withhelloid 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 theheadtag.
<!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>回答4:
Just put your JS in window.onload
window.onload = function() {
what();
function what() {
document.getElementById('hello').innerHTML = 'hi';
};
}
回答5:
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.
回答6:
<!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>回答7:
The JavaScript Part Need To Run Once Page Is Loaded Therefor It Is Advised To Place JavaScript Script At The End Of 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>回答8:
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>回答9:
You could try using the setTimeout method to make sure your html loads first.
回答10:
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>
回答11:
<!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>回答12:
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.
回答13:
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 :)
回答14:
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.
回答15:
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.
回答16:
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.
来源：https://stackoverflow.com/questions/18239430/cannot-set-property-innerhtml-of-null