JS is not working [duplicate] - javascript

This question already has answers here:
Why does jQuery or a DOM method such as getElementById not find the element?
(6 answers)
Closed 6 years ago.
I don't understand why simple code is not working is my browser.
<head>
<script src="../static/js/jquery-1.12.3.min.js" ></script>
<script src="../static/js/jquery-ui.min.js"></script>
<link href="../static/js/jquery-ui.min.css" rel="stylesheet"/>
<script>
$("#totalCart").html("99,75");
</script>
</head>
<body>
<div id="totalCart">Total </div>
</body>
when I start this code in Chrome I see nothing, why?

You're using a selection before DOM is loaded.
The good practice is to include all script at the end of your body.
Or you can use
$(document).ready(function(){
//your code
});

Try putting
<script>
$("#totalCart").html("99,75");
</script>
just before
</body>
Explanation:
For jQuery to grab an element via $("#totalCart") - and, likewise, for non-library javascript to grab an element via document.getElementById('totalCart') - that element has to first exist.
In your original structure, the script runs as soon as it is parsed - but this happens before the element is parsed... effectively, at the moment the script runs, the element does not yet exist.
By the time the element is parsed and does exist, the script has already run and it is not invoked a second time.
If you place the <script> at the very end of the document (just before <body>) then all elements will already have been parsed by the browser rendering engine and they will exist.

Related

How to call javascript and write it on html? [duplicate]

This question already has answers here:
Why does jQuery or a DOM method such as getElementById not find the element?
(6 answers)
Closed 3 years ago.
so I'm using this Javascript (API) that has a bunch of function. How do I go about writing it to an HTML file?
so one of the function is "api.ping()" which works fine on powershell, but I cant get it to print that in an HTML file.
So in the script I wrote
document.getElementById("demo").innerHTML = api.ping();
and the HTML is
<!DOCTYPE html>
<html>
<body>
<script type="index.js"></script>
<p id="demo"></p>
</body>
</html>
I'm trying to put the value returned from the call onto the HTML file.
I think your index.js file is probably not being included. You'll want to change the tag line to read:
<script type="text/javascript" src="index.js"></script>
Assuming that index.js is in the same directory as this HTML file.

Basic code not working with jQuery [duplicate]

This question already has answers here:
Why does jQuery or a DOM method such as getElementById not find the element?
(6 answers)
Closed 6 years ago.
I am very new to jQuery, literally just trying to get it to work for the first time. Only the alert box works, but none of the other very simple methods I am trying out. Here are the files:
HTML:
<!DOCTYPE HTML>
<html>
<head>
<title>jquery</title>
<script type="text/javascript" src="jquery-3.1.0.min.js"></script>
<script type="text/javascript" src="myJavaScript.js"></script>
</head>
<body>
<h1 id="title">This is a title</h1>
<p> This is some sample text.</p>
</body>
</html>
JavaScript file:
$(document).ready(function (){alert("this works!")});
$("#title").text("but this is not not working");
As you can see the example can't be simpler. I have off course downloaded the jquery-3.1.0.min.js file and put it in the same folder as the html. If I comment out the link, the alert stops working, so I now the file is being referenced OK. Why is the second line of jQuery not working? Many thanks, P
Because the DOM(the entire structure of your application) isn't loaded yet. You need to use a $(document).ready(makes sure the DOM is loaded before running jQuery code) or an event handler to make the change visible.

Cannot set property "onchange" of null [duplicate]

This question already has answers here:
Why does jQuery or a DOM method such as getElementById not find the element?
(6 answers)
Closed 9 years ago.
I'm trying to get the element with getElementById(), but it returns null even though the element exists. What am I doing wrong?
<html>
<head>
<title>blah</title>
<script type="text/javascript">
alert(document.getElementById("abc"));
</script>
</head>
<body>
<div id="abc">
</div>
</body>
You have to put this in a document load event. The DOM hasn't gotten to abc by the time the script is executed.
Your script runs before the DOM has been loaded. To fix this you can place your code in the window.onload function like so:
window.onload = function() {
alert(document.getElementById("abc"));
};
An alternative is to place your script right before the closing </body> tag.
If you don't want to attach to the load event then simply put your script at the bottom of the body, so it will execute at the end-
<html>
<head>
<title>blah</title>
</head>
<body>
<div id="abc">
</div>
<script type="text/javascript">
alert(document.getElementById("abc"));
</script>
</body>
</html>
This is because the script runs before the page has rendered.
For proof add this attribute to the body tag:
<body onload="alert(document.getElementById('abc'));" >
But it doesn't exist, not at that point in the HTML. HTML documents are parsed top-to-bottom, just like programs run. The best solution is just to put your script tag at the bottom of the page. You could also attach your JavaScript to the onload event.

Beginner javascript text display [duplicate]

This question already has answers here:
Code working in jsFiddle but not in browser
(2 answers)
Closed 9 years ago.
I am having a problem with my JavaScript, when I put it into JSFiddle it works fine. But it wont work locally? Here is the fiddle: http://jsfiddle.net/4Ukkz/
var String = "preacher preacher, 5th grade teacher";
document.getElementById('text').innerHTML=String;
So the problem is. In the JSFiddle, the text will display, But locally nothing will display.
Note. It works in the fiddle. but not on my computer
In JSFiddle, your code is automatically wrapped with
window.onload = function() {
// your code
};
This is necessary because in your code, script.js is included above <div id="text"></div>. If you don't wait until that element exists, document.getElementById('text') will return null and the attempt to set innerHTML will fail.
The solution is to wrap your code as above or move your script tag below the div.
May be you don't have a script.js file with the javascript code you pasted in the fiddle?
And move the script element after your body. So your JavaScript code runs after all the elements in the body have been created.
So something like this:
<html>
<title>hi</title>
<head>
<link rel="stylesheet" type="text/css" href="style.css" />
</head>
<body>
<div id="text"></div>
</body>
<script type='text/javascript' src='script.js'></script>
</html>

where to embed javascript section in a html page [duplicate]

This question already has answers here:
when and where to put javascript in html
(7 answers)
Closed 9 years ago.
the thing is i'm unable to figure out where to embed javascript in html page whether in head section or body section.
example 1:
<html>
<head>
<title>events</title>
<script>
document.getElementById("b").onclick=function(){displayDate()};
function displayDate()
{
document.getElementById("demo").innerHTML=Date();
}
</script>
</head>
<body>
<p id="demo"></p>
<button id="b">new</button>
</body>
</html>
in the above example I placed script tags in head section but it is not working.
example: 2
<html>
<head>
<title>events</title>
<script>
function upper()
{
var x=document.getElementById("t");
x.value=x.value.toUpperCase();
}
</script>
</head>
<body >
enter some text:<input type="text" id="t" onChange="upper()"/>
</body>
</html>
in the second example I placed the javascript in head section it is working properly.first example demonstrates that on clicking a button date will be displayed in the second example in a text box when data is entered and if we come out of the box the letters in the box will we converted to uppercase.
To have it more readable I prefer to always place JavaScript in the head section. If you need to access elements from there, use the window.onload event:
<head>
<title>events</title>
<script type="text/javascript">
window.onload = function() {
document.getElementById("b").onclick = function() {
displayDate();
};
};
function displayDate()
{
document.getElementById("demo").innerHTML=Date();
}
</script>
</head>
This would work just fine.
Your second example worked because you just defined a function, you didn't try to access any element.
You can put it in the head. The problem is that your examples are not the same. The first one doesn't work because the current date is retrieved by calling Date(), when it should be new Data().getDate(). The second example works because the code is valid.
The problem you're running into is that you're trying to reference an element before it is loaded into the DOM.
When you're putting the script in the HEAD tag, the dom hasn't been loaded yet and the document.getElementById won't find what you're looking for.
You have a few different options to deal with this. You can put the script at the end of the page, which will work for your small example here.
Probably a better option is to take a look at learning/using jquery or another js utility. Jquery makes it easy to solve this issue by giving you a "ready" event. This ready event will be triggered when the DOM is fully loaded. So:
$(document).ready(
function()
{
$("#demo").html((new Date()).toString());
});
Is all you really need. With this approach, it doesn't matter where the script it on the page.

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