How do I call the JavaScript function properly? - javascript

<!DOCTYPE html>
<html lang="en">
<head>
<title>JavaScript Example</title>
<script>
function displayString() {
return "<h1>Main Heading</h1>"
}
displayString();
document.write("Execute during page load from the head<br>");
</script>
</head>
<body>
<script>
document.write("Execute during page load from the body<br>");
</script>
</body>
</html>
So this is my problem. No matter where I put the displayString(), the h1 just never seems to show up on the browser. Can anybody please help me see where I am wrong? I am new to JavaScript. Oh, and what I am trying to do is to call the function.

You need to write the returned String to the document:
<!DOCTYPE html>
<html lang="en">
<head>
<title>JavaScript Example</title>
<script>
function displayString() {
return "<h1>Main Heading</h1>"
}
document.write(displayString());
document.write("Execute during page load from the head<br>");
</script>
</head>
<body>
<script>
document.write("Execute during page load from the body<br>");
</script>
</body>
</html>

No matter where I put the displayString(), the h1 just never seems to
show up on the browser.
If you wish to add a new element to a document, several approaches are available:
document.write (effectively deprecated)
.innerHTML (sometimes useful, but can be slow)
DOM API - recommended approach
The recommended approach is to use the DOM API.
DOM stands for Document Object Model. Essentially it's the markup of your document represented as a tree-like structure of nodes. There are many DOM API functions which allow you to:
add
remove
append
prepend
insert
update
new DOM nodes.
Any DOM node may be added, removed or updated, including:
parent elements
child elements
sibling elements
element attributes
ids, classNames, classLists
custom data-* attributes
text nodes
Here is an example:
function displayMainHeading () {
let mainHeading = document.createElement('h1');
mainHeading.textContent = 'Main Heading';
document.body.prepend(mainHeading);
}
displayMainHeading();
<p>Paragraph 1</p>
<p>Paragraph 2</p>
Further Reading
This is a good primer to get you started:
A Beginners Guide To DOM Manipulation by Iqra Masroor

Related

how to isolate js script from the html code?

i'd like to isolate the javascript code from the html code in two diferent files, originally I had this code:
<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
</head>
<body>
<p id="body">HTML Text</p>
</body>
</html>
<script>
$(document).ready(function () {
$("#body").text("JS Text");
});
</script>
and the output of the <-p-> was the expected "JS Text".
Then I tried to isolate the js script to another file (script.js):
window.onload = function(){
var text = document.getElementById('body');
text.innerHTML ='JS Text';
}
I've also make the reference at the html file:
<script type="text/javascript"src="scripts.js"></script>
but then the output text is no longer the expected (JS Text) but (HTML text)
what else do I need to make the js script work again?
First, it is invalid to place anything after the closing HTML tag, so while your first bit of code worked, it was invalid.
If you remove the JavaScript and place it in its own file, it will continue to work as long as you reference the file properly (use a relative reference and test the file on a web server) and place the script element just prior to the closing body tag so that when the script is processed and attempts to find the right DOM element, the DOM will have been loaded at that time.
FYI:
If you have JQuery in the referenced script file, then your
script that references JQuery will need to occur in the HTML prior
to the script that uses it.
The type attribute in the script tag has not been needed in
several years.
It's not a good idea to name anything body so that you won't cause
confusion with the body element.
Don't use .innerHTML when the string you are working with doesn't
contain any HTML. .innerHTML has security and performance
implications. Use .textContent instead.
<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
</head>
<body>
<p id="body">HTML Text</p>
<script src="relativePathToFile.js"></script>
</body>
</html>

document.getElementsByTagName returning undefined on placing the script after body

I know that this is a frequently asked question.
I have tried all the methods like using onload() for body tag,
placing the script after the DOM elements and using self invoking function.
Yet I get that my element is undefined.
P.S: document.getElementsByTagName('') replaced with document.getElementById('') works fine. Why is that? Please explain both of my doubts. Here is my simple code
<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body onload="loadHandler()">
<p>Drag me!</p>
<script type="text/javascript">
function loadHandler() {
document.getElementsByTagName('p').setAttribute('draggable', true);
}
</script>
</body>
</html>
getElementsByTagName (as the name suggests) returns an array of elements. If you want the first one, take the first one.
.highlight{ color: red}
<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body onload="loadHandler()">
<p>Drag me!</p>
<script type="text/javascript">
function loadHandler() {
var elem = document.getElementsByTagName('p')[0];
elem.setAttribute('draggable',true)
elem.classList.add('highlight');
}
</script>
</body>
</html>
As for why dragging is not working, perhaps the documentation might shed some light
By default, only text selections, images, and links can be dragged. For all others elements, the event ondragstart must be set for the drag and drop mechanism to work, as shown in this comprehensive example.
getElementsByTagName returns array of results, not just a single result like getElementById. Try to use getElementsByTagName('p')[0].

Nested iframes, AKA Iframe Inception

Using jQuery I am trying to access div id="element".
<body>
<iframe id="uploads">
<iframe>
<div id="element">...</div>
</iframe>
</iframe>
</body>
All iframes are on the same domain with no www / non-www issues.
I have successfully selected elements within the first iframe but not the second nested iframe.
I have tried a few things, this is the most recent (and a pretty desperate attempt).
var iframe = jQuery('#upload').contents();
var iframeInner = jQuery(iframe).find('iframe').contents();
var iframeContent = jQuery(iframeInner).contents().find('#element');
// iframeContent is null
Edit:
To rule out a timing issue I used a click event and waited a while.
jQuery().click(function(){
var iframe = jQuery('#upload').contents().find('iframe');
console.log(iframe.find('#element')); // [] null
});
Any ideas?
Thanks.
Update:
I can select the second iframe like so...
var iframe = jQuery('#upload').contents().find('iframe');
The problem now seems to be that the src is empty as the iframe is generated with javascript.
So the iframe is selected but the content length is 0.
Thing is, the code you provided won't work because the <iframe> element has to have a "src" property, like:
<iframe id="uploads" src="http://domain/page.html"></iframe>
It's ok to use .contents() to get the content:
$('#uploads).contents() will give you access to the second iframe, but if that iframe is "INSIDE" the http://domain/page.html document the #uploads iframe loaded.
To test I'm right about this, I created 3 html files named main.html, iframe.html and noframe.html and then selected the div#element just fine with:
$('#uploads').contents().find('iframe').contents().find('#element');
There WILL be a delay in which the element will not be available since you need to wait for the iframe to load the resource. Also, all iframes have to be on the same domain.
Hope this helps ...
Here goes the html for the 3 files I used (replace the "src" attributes with your domain and url):
main.html
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>main.html example</title>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<script>
$(function () {
console.log( $('#uploads').contents().find('iframe').contents().find('#element') ); // nothing at first
setTimeout( function () {
console.log( $('#uploads').contents().find('iframe').contents().find('#element') ); // wait and you'll have it
}, 2000 );
});
</script>
</head>
<body>
<iframe id="uploads" src="http://192.168.1.70/test/iframe.html"></iframe>
</body>
iframe.html
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>iframe.html example</title>
</head>
<body>
<iframe src="http://192.168.1.70/test/noframe.html"></iframe>
</body>
noframe.html
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>noframe.html example</title>
</head>
<body>
<div id="element">some content</div>
</body>
var iframeInner = jQuery(iframe).find('iframe').contents();
var iframeContent = jQuery(iframeInner).contents().find('#element');
iframeInner contains elements from
<div id="element">other markup goes here</div>
and iframeContent will find for elements which are inside of
<div id="element">other markup goes here</div>
(find doesn't search on current element) that's why it is returning null.
Hey I got something that seems to be doing what you want a do. It involves some dirty copying but works. You can find the working code here
So here is the main html file :
<!DOCTYPE html>
<html>
<head>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<script type="text/javascript">
$(document).ready(function(){
Iframe = $('#frame1');
Iframe.on('load', function(){
IframeInner = Iframe.contents().find('iframe');
IframeInnerClone = IframeInner.clone();
IframeInnerClone.insertAfter($('#insertIframeAfter')).css({display:'none'});
IframeInnerClone.on('load', function(){
IframeContents = IframeInner.contents();
YourNestedEl = IframeContents.find('div');
$('<div>Yeepi! I can even insert stuff!</div>').insertAfter(YourNestedEl)
});
});
});
</script>
</head>
<body>
<div id="insertIframeAfter">Hello!!!!</div>
<iframe id="frame1" src="Test_Iframe.html">
</iframe>
</body>
</html>
As you can see, once the first Iframe is loaded, I get the second one and clone it. I then reinsert it in the dom, so I can get access to the onload event. Once this one is loaded, I retrieve the content from non-cloned one (must have loaded as well, since they use the same src). You can then do wathever you want with the content.
Here is the Test_Iframe.html file :
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<div>Test_Iframe</div>
<iframe src="Test_Iframe2.html">
</iframe>
</body>
</html>
and the Test_Iframe2.html file :
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<div>I am the second nested iframe</div>
</body>
</html>
You probably have a timing issue. Your document.ready commend is probably firing before the the second iFrame is loaded. You dont have enough info to help much further- but let us know if that seems like the possible issue.
You should use live method for elements which are rendered later, like colorbox, hidden fields or iframe
$(".inverter-value").live("change",function() {
elem = this
$.ajax({
url: '/main/invertor_attribute/',
type: 'POST',
aysnc: false,
data: {id: $(this).val() },
success: function(data){
// code
},
dataType: 'html'
});
});
I think the best way to reach your div:
var your_element=$('iframe#uploads').children('iframe').children('div#element');
It should work well.
If browser supports iframe, then DOM inside iframe come from src attribute of respective tag. Contents that are inside iframe tag are used as a fall back mechanism where browser does not supports iframe tag.
Ref: http://www.w3schools.com/tags/tag_iframe.asp
I guess your problem is that jQuery is not loaded in your iframes.
The safest approach is to rely on pure DOM-based methods to parse your content.
Or else, start with jQuery, and then once inside your iframes, test once if typeof window.jQuery == 'undefined', if it's true, jQuery is not enabled inside it and fallback on DOM-based method.

Get the content of another page's div with jQuery Ajax

I would like page.html to ajax-request the content of side.html and extract the content of two of its divs. But I cannot find the correct way to parse the response, despite everything I tried.
Here is side.html:
<!DOCTYPE html>
<html>
<head>
<title>Useless</title>
</head>
<body>
<div id="a">ContentA</div>
<div id="b">ContentB</div>
</body>
</html>
and here is page.html
<!DOCTYPE html>
<html>
<head>
<title>Useless</title>
<script type='text/javascript' src='jquery-1.9.0.min.js'></script>
</head>
<body>
Hello
<script type="text/javascript">
jQuery.ajax({
url: "side.html",
success: function(result) {
html = jQuery(result);
alert(html.find("div#a").attr("id"));
alert(html.find("div#a").html());
alert(html.find("div#a"));
},
});
</script>
</body>
</html>
When I access this page, I get no error, and the three alert()s yield undefined, undefined and [object Object]. What am I doing wrong? Example is live here.
You need to change this line:
html = jQuery(result);
To this:
html = jQuery('<div>').html(result);
And actually, even better you should declare this as a local variable:
var html = jQuery('<div>').html(result);
Explanation
When you do jQuery(result), jQuery pulls the children of the <body> element and returns a wrapper around those elements, as opposed to returning a jQuery wrapper for the <html> element, which I tend to agree would be pretty dumb.
In your case, the <body> of sidebar.html contains several elements and some text nodes. Therefore the jQuery object that is returned is a wrapper for those several elements and text nodes.
When you use .find(), it searches the descendants of the elements wrapped by the jQuery object that you call it on. In your case, the <div id="a"> is not one of these because it is actually one of the selected elements of the wrapper, and cannot be a descendant of itself.
By wrapping it in a <div> of your own, then you push those elements "down" a level. When you call .find() in my fixed code above, it looks for descendants of that <div> and therefore finds your <div id="a">.
Comment
If your <div id="a"> was not at the top level, i.e. an immediate child of the <body>, then your code would have worked. To me this is inconsistent and therefore incorrect behaviour. To solve this, jQuery should generate the container <div> for you, when it is working its <body> content extraction magic.
Try this :
$.get(url,function(content) {
var content = $(content).find('div.contentWrapper').html();
...
}

Javascript: Can't get element using getElementById [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.
Ok. I need fresh eyes because I'm still on this s***d problem for one hour!
Here is my simple HTML code (testssio.html) that include javascript script:
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
var ssio = document.getElementById('ssio');
ssio.html = "it finally works!";
</script>
</head>
<body>
<div id="ssio"></div>
</body>
</html>
But it doesn't work! Using the debugger, I get:
Uncaught TypeError: Cannot set property 'html' of null /testssio/:6
Does anyone get it? I know it's not the correct place to look for debugging help, but I'll be crazy if I don't get it! So please, any help?
Tahnks in advance.
The reason for this is that scripts in the head load before the page is rendered. This means your content is not yet rendered and therefore not a part of document.
If you want to see this work, try moving your script below the element renders, like this:
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<div id="ssio"></div>
<script type="text/javascript">
var ssio = document.getElementById('ssio');
ssio.innerHTML = "it finally works!";
</script>
</body>
</html>
A more standardized way of doing this is with events. Many people use jQuery but it can be done with plain js. This would mean changing your script like this:
<script type="text/javascript">
function WinLoad() {
var ssio = document.getElementById('ssio');
ssio.innerHTML = "It finally works!";
}
window.onload = WinLoad;
</script>
This way you can still leave it in the <head>.
Also, using .html is from jQuery. It is generally used as .html(content). If you want to use the plain javascript version use .innerHTML = content.
I mention jQuery so much because it is a highly used API. This quote is from their site:
jQuery is a fast and concise JavaScript Library that simplifies HTML document traversing, event handling, animating, and Ajax interactions for rapid web development. jQuery is designed to change the way that you write JavaScript.
Your code is running too early before the DOM is loaded and thus document.getElementById() doesn't find the element in the document yet.
You can either move your script tag down to right before the </body> tag or you can wait for the DOM to load before running your code with either the window onload event or a DOMReady event.
There are two errors here. First, you need to put the SCRIPT tag after the element. Second, it's not .html, but .innerHTML. So here is the corrected code:
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<div id="ssio"></div>
<script type="text/javascript">
var ssio = document.getElementById('ssio');
ssio.innerHTML = "it finally works!";
</script>
</body>
</html>
you can use something like this
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
document.onload= function(){
var ssio = document.getElementById('ssio');
ssio.html = "it finally works!";
}
</script>
</head>
<body>
<div id="ssio"></div>

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