I've read many tutorials and tried them, but they don't work.
Just for example I wrote this simple code:
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<p id="testElement"> Html text</p>
<script>
var paragraph = document.getElementById("testElement");
paragraph.innerHTML = "Test Message";
</script>
</body>
</html>
I get Test Message text in my page.
Then I put my JS code to an external file: '/js/js.js'
var paragraph = document.getElementById("testElement");
paragraph.innerHTML = "Test Message";
And modify the HTML file to:
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" src="/js/js.js"></script>
</head>
<body>
<p id="testElement"> Html text</p>
</body>
</html>
When I open the HTML file in a browser, I only get Html text. My JS does not work. Please explain what I am doing wrong.
Your problem is that javascript linked in head is executed before the body is loaded, so you can just put the script at the end of the body like this:
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<p id="testElement"> Html text</p>
<script type="text/javascript" src="js/js.js"></script>
</body>
</html>
Check the JavaScript error console.
Your code runs before the document is rendered so the node testElemet doesn't exist.
Either move your script-include down as the last element in the body or wrap your code in a load/ready event.
function on_document_ready(callback) {
if (document.readyState === "complete") {
callback();
} else {
document.addEventListener("DOMContentLoaded", callback);
}
}
on_document_ready(function () {
var paragraph = document.getElementById("testElemet");
paragraph.innerHTML = "Test Message";
});
This should work fine:
var paragraph = document.getElementById("testElement");
paragraph.innerHTML = "Test Message";
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<p id="testElement">Html text</p>
<script type="text/javascript" src="/js/js.js"></script>
</body>
</html>
Please make sure that <script type="text/javascript" src="/js/js.js"></script> is placed just before </body>.
Try this
var doSomething = function()
{
var paragraph = document.getElementById("testElement");
paragraph.innerHTML = "Test Message";
}
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" src="js.js"></script>
</head>
<body onload = "doSomething();">
<p id="testElement"> Html text</p>
</body>
</html>
Try saving both the files in the same folder.
Make use of your browsers developer console, to determine whether any errors have occurred.
Regarding 'onload', you can have a look at this link.
Related
I have written a JavaScript alert message code it displays the alert message first in both codes 1 and 2 before Html content. What should I do to run the HTML content first and then a javascript code?
Code 1
<!DOCTYPE html>
<html>
<head>
<title>Hello, World !</title>
</head>
<body>
<h1>I am learning JavaScript.</h1>
<div id="Content">
<p>This is a paragraph tag. Here the content of html.</p>
</div>
<script src="text.js"></script>
</body>
</html>
Code 2
<!DOCTYPE html>
<html>
<head>
<title>Hello, World !</title>
</head>
<body>
<h1>I am learning JavaScript.</h1>
<div id="Content">
<p>This is a paragraph tag. Here the content of html.</p>
</div>
<script>
alert(" This is alert message.");
</script>
</body>
</html>
There is a load event, which will fire AFTER the page is loaded. You can listen to the event:
window.addEventListener('load', function() {
console.log('All assets are loaded');
alert ("This is an alert MSG");
})
You can use setTimeout() for this
<html>
<head>
<title>Hello, World !</title>
</head>
<body>
<h1>I am learning JavaScript.</h1>
<div id="Content">
<p>This is a paragraph tag. Here the content of html.</p>
</div>
<script>
setTimeout(()=>{
alert(" This is alert message.")
},2000)
</script>
</body>
</html>
You can use window.onload function. This function called after body load.
<!DOCTYPE html>
<html>
<head>
<title>Hello, World !</title>
</head>
<body>
<h1>I am learning JavaScript.</h1>
<div id="Content">
<p>This is a paragraph tag. Here the content of html.</p>
</div>
<script>
window.onload = function () {
alert(" This is alert message.");
}
</script>
</body>
</html>
In your first code just put defer attribute as below
<script defer src="text.js"></script>
A script that will be downloaded in parallel to parsing the page, and executed after the page has finished parsing
for more detail refer to the URL
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script
create your Script like below
<script type = "text/javascript">
function displayalert() {
alert ("This is an alert MSG");
}
</script>
add this code in your body(this is a button)
<input type = "button" value = "Click me" onclick = "displayalert();" />
when you click on this button you will see the alert
We are using the onclick attribute and call the displayalert() function where the alert() is defined.
<!DOCTYPE html>
<html>
<head>
<script>
document.getElementById("passage").innerHTML = "Paragraph changed!";
</script>
</head>
<body>
<div id="passage">hello</div>
<div id="question"></div>
<div id="answers"></div>
</body>
</html>
Why is document.getElementById("passage").innerHTML = "Paragraph changed!" not working for me? I just end up with a blank screen, not even the original "hello".
Your script is called before the element is loaded, try calling the script after loading element
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<div id="passage">hello</div>
<div id="question"></div>
<div id="answers"></div>
<script>
document.getElementById("passage").innerHTML = "Paragraph changed!";
</script>
</body>
</html>
If you check the console, you can see an error
Uncaught TypeError: Cannot set property 'innerHTML' of null
That is the HTML page is parsed and executed top down.
So, it can't identify what is the element you are mentioning.
So, you should either use an EventListener or place the script just before the end of body tag
Method 1 Event Listener
<!DOCTYPE html>
<html>
<head>
</head>
<script>
window.onload=function(){
document.getElementById("passage").innerHTML = "Paragraph changed!";
};
</script>
<body>
<div id = "passage">hello</div>
<div id = "question"></div>
<div id = "answers"></div>
</body>
</html>
Method 2 : script is just above body tag
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<div id = "passage">hello</div>
<div id = "question"></div>
<div id = "answers"></div>
<script>
document.getElementById("passage").innerHTML = "Paragraph changed!";
</script>
</body>
</html>
You script should be executed once the page is loaded.
Otherwise all elements of the page may not be still attached to the dom when you refer to them.
Rather than moving the script after the element declaration that may be error prone (you should always be aware of the order of script), you could use
event designed to be executed after the dom is totally loaded.
For example onload attribute of body :
<body onload='document.getElementById("passage").innerHTML = "Paragraph changed!";'>
Your script is calling before element is loaded.
Try
$(document).ready(function()
{
document.getElementById("passage").innerHTML = "Paragraph changed!";
});
JS:
(function(){
document.getElementById("passage").innerHTML = "Paragraph changed!";
})
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
if (document.getElementById("popup")) {
window.alert("hi");
}
</script>
</head>
<body>
<h1 id="popup">dfdfs</h1>
</body>
</html>
i have a simple javascript which shows alert when the h1 id exits ,but i am not getting the alert message.code in jquery also can help.
Put your <script> tag at the end of the body:
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<h1 id="popup">dfdfs</h1>
<script type="text/javascript">
if (document.getElementById("popup")) {
window.alert("hi");
}
</script>
</body>
</html>
Write your script after the element so that it runs after element is present. See the code:
<!DOCTYPE html>
<html>
<body>
<h1 id="popup">dfdfs</h1>
<script type="text/javascript">
if (document.getElementById("popup")) {
window.alert("hi");
}
</script>
</body>
</html>
Plunkr for the same is: "http://plnkr.co/edit/0fznytLHtKNuZNqFjd5G?p=preview"
Because, you're executing the script before document is completely loaded, the element #popup is not found.
Use DOMContentLoaded
Use DOMContentLoaded to check if the DOM is completely loaded.
<script type="text/javascript">
document.addEventListener("DOMContentLoaded", function(event) {
console.log("DOM fully loaded and parsed");
if (document.getElementById("popup")) {
window.alert("hi");
}
});
</script>
Using jQuery ready
Using jQuery, you can use ready method to check if DOM is ready.
$(document).ready(function() {
if ($("#popup").length) {
window.alert("hi");
}
});
Moving script to the end of body
You can move your script to the end of body.
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<h1 id="popup">dfdfs</h1>
// Move it here
<script type="text/javascript">
if (document.getElementById("popup")) {
window.alert("hi");
}
</script>
</body>
</html>
Your script is above the h1 element that you're trying to retrieve. Because of this, it is being run before the element actually exists.
Either move the script to the bottom of the page, or wrap it in a jQuery ready block. And consider moving it to an external file.
$(function() {
if(document.getElementById("popup")) {
window.alert("hi");
}
});
try this easy way. no need of jquery.
<html>
<head>
</head>
<body>
<h1 id="popup">dfdfs</h1>
<script type="text/javascript">
if(document.getElementById("popup")) {
window.alert("hi");
}
</script>
</body>
</html>
It is good practice to use the <script> tags in <body> because it improves the performance by loading it quicker.
And then use
<body>
<script>
$(function() {
if(document.getElementById("popup")) {
window.alert("hi");
}
});
</script>
</body>
Below code gives you solution
$(document).ready(function() {
if (document.getElementById("popup")) {
window.alert("hi");
}
});
So we can do:
<html>
<head>
<title>JavaScript Popup Example 3</title>
</head>
<script type="text/javascript">
function exitpop()
{
my_window = window.open("", "mywindow1", "status=1,width=350,height=150");
//my_window.document.write('somehow add JS');
my_window.document.write('<h1>Popup Test!</h1><br/>');
my_window.document.write('J_\alpha(x) = \sum_{m=0}^\infty \frac{(-1)^m}{m! \, \Gamma(m + \alpha + 1)}{\left({\frac{x}{2}}\right)}^{2 m + \alpha} ');
}
</script>
<body onunload="javascript: exitpop()" >
<h1>JavaScript Popup Example 4</h1>
</body>
</html>
but how to for example add to header of that html page with something like <script type="text/javascript" src="path-to-MathJax/MathJax.js"></script> to enable MathML and tex formulas rendering?
Yep, you just need to concatenate the script tags, like so: jsfiddle demo
The money-shot code sample is:
jswin = window.open("", "jswin", "width=350,height=150");
jswin.document.write("Here's your popup!");
jswin.document.write('<scr'+'ipt>alert("Here\'s your alert()!");</scr'+'ipt>');
Use javascript to create a node named script, and sets it's attributes with javascript. Then append the node to document.head.
<html>
<head>
<title>JavaScript Popup Example 3</title>
</head>
<script type="text/javascript">
function exitpop()
{
var my_window = window.open("", "mywindow1", "status=1,width=350,height=150");
var head = my_window.document.getElementsByTagName("head").item(0);
alert(head.innerHTML);
var script = my_window.document.createElement ("script");
script.src = "a.js";
head.appendChild (script);
alert(head.innerHTML);
}
</script>
<body onunload="javascript: exitpop()" >
<h1>JavaScript Popup Example 4</h1>
</body>
</html>
You can consider using an iframe, you can set its head and body altogether, and you can put it in the window.
I'm working on a Chrome extension where I need to pass highlighted text into a browser_action. I found the following code in a Google Group, and at the time it was written it was still valid - but it doesn't work anymore..
Does anyone know an alternative solution?
background.html:
<html>
<head>
<script type="text/javascript">
var selection_callbacks = [];
function getSelection(callback) {
selection_callbacks.push(callback);
chrome.tabs.executeScript(null, { file: "contentscript.js" });
};
chrome.extension.onRequest.addListener(function (request) {
var callback = selection_callbacks.shift();
callback(request);
});
</script>
</head>
<body>
</body>
</html>
popup.html:
<html>
<head>
<script type="text/javascript">
function onSelection(text) {
document.getElementById("output").innerHTML = text;
}
chrome.extension.getBackgroundPage().getSelection(onSelection);
</script>
</head>
<body>
<div id="output">
This should be replaced with the selected text
</div>
</body>
</html>
contentscript.js:
chrome.extension.sendRequest(window.getSelection().toString());
You could use a real content script instead of injecting JavaScript into the page with chrome.extension.executeScript. You could then have background.html ask the content script for the selection using chrome.tabs.sendRequest.