Alright so first off, total Newbie here, so my questions answer might be extreemley simple because i have missed some thing critical.
I am trying to have a switch statement, switch out the innerHTML of an h1 tag with an id="bbref". I set the userName Variable to "Lister" and created my switch statement to write a different line into the h1 tag base don what name was input for userName.
for some reason however my code is just not working... any thoughts.. or noticeable brain-farts on my end?
here is the code:
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Javascript Learning</title>
<script type="text/javascript">
var userName = "Lister";
switch (userName) {
case "Lister" :
document.write.getElementById("bbref").innerHTML = "Lister Is the Man!";
break;
case "Rimmer":
document.write.getElementById("bbref").innerHTML = "Rimmer is a Smeg head...";
break;
default :
doacument.write.getElementById("bbref").innerHTML = "It's all about \"The Cat\""
}
</script>
</head>
<body>
<header></header>
<section>
<article>
<h1 id="bbref">Test Title</h1>
</article>
</section>
<footer></footer>
</body>
</html>
You're messing up your functions a little there, change:
document.write.getElementById("bbref").innerHTML = "Lister Is the Man!";
to:
document.getElementById("bbref").innerHTML = "Lister Is the Man!";
And so on for the rest.
document.getElementById("bbref") will fetch the element and .innerHTML will be the HTML inside the element, changing it will directly change the visible HTML. So there's no need to write anything.
Fiddle:
http://jsfiddle.net/H4hzE/
window.onload/$(document).ready()
The other issue you would be having here is that your javascript code is executing before your HTML is rendering. Bind your code to window.onload or $(document).ready() (if using jQuery) to run the code after the page loads.
window.onload Examples:https://developer.mozilla.org/en-US/docs/DOM/window.onload
jQuery's $(document).ready():http://api.jquery.com/ready/
Fiddle (using window.onload):
http://jsfiddle.net/H4hzE/1/
Since you say you're new to JavaScript, it's probably worthwhile sharing some info regarding document.write() as I think you may have misunderstood it's functionality a little bit. :)
http://www.w3schools.com/jsref/met_doc_write.asp
http://javascript.info/tutorial/document-write
https://developer.mozilla.org/en-US/docs/DOM/document.write
document.write() and document.getElementById() are two different methods. In this case you just want to use getElementById, so omit the .write in all 3 cases, e.g.:
document.getElementById("bbref").innerHTML = "Lister Is the Man!";
Related
I don't know how to declare a variable here in javascript. I have an example situation that if the paragraph is equals to a, the alert will popup.
<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body>
<p id="sample">a</p>
</body>
</html>
<script type="text/javascript">
var sample = getElementById('sample');
if (sample == "a") {
alert("Correct")
};
</script>
You're declaring your variable just fine, however if you want the text within the element, you also need to use the innerHTML property. And when you use the getElementById method, you need to use it on the document object like document.getElementById:
var sample = document.getElementById('sample');
if (sample.innerHTML == "a") {
alert("Correct")
};
<p id="sample">a</p>
sample is a variable and you are correct but it is storing a reference to a DOM Element with id sample. To get the inner html of that you need
var sample = getElementById('sample').innerHTML;
Also, use === over == for no casting etc. Refer here
I will recommend you to have a quick look at JS from w3schools and then move to MDN. Nobody will report you here if you show your efforts, so relax :).
Your declaration is fine, but the assignment part is missing document as the object which has the .getElementById method. Then, once you have the reference to the element, you then need to access its content with .textContent (you can't compare the entire element to a value that the element might contain). As a side note on this, when the string you wish to set/get doesn't contain any HTML, you should use .textContent so that the browser doesn't parse the string for HTML unnecessarily. Often, people will suggest that the content of an element should be gotten/set using .innerHTML and, while that will work, it's wasteful if the string doesn't contain any HTML.
Also, the <script> must be located within the head or the body, not outside of them. I would suggest placing it just prior to the closing body tag so that by the time the processing reaches the script, all of the HTML elements have been parsed into memory and are available.
Lastly (and this is really just a side point), an HTML page also needs the title element to have something in it, otherwise it won't be valid. While browsers don't actually do HTML validation, it's important to strive for valid HTML so that you can be sure that your pages will work consistently across all devices. You can validate your HTML at: http://validator.w3.org.
<!DOCTYPE html>
<html>
<head>
<title>Something Here</title>
</head>
<body>
<p id="sample">a</p>
<script type="text/javascript">
var sample = document.getElementById('sample');
if (sample.textContent == "a") {
alert("Correct")
};
</script>
</body>
</html>
So basically I want to change image in every 5 second, so I wrote the following Javascript code and tag it to html. But the console keep saying that "No javaScript on this page" and the code does not apply
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>JavaScript for Programmers</title>
</head>
<body>
<h2>Mood Change</h2>
<p>The mood of this web page changes every 5 seconds.</p>
<p><img id="mood" src="frown.gif" alt="mood"></p>
<script async src="../scripts/moody.js"></scripts>
</body>
</html>
var images=[]
images[0]="smile.gif";
images[1]="frown.gif";
var myMood= document.getElementById("mood");
function change(){
if(myMood==images[0]){
myMood.src=images[1];
}
else if(myMood.src==imgaes[1]){
myMood.src=images[0];
}
}
setInterval(change,5000);
</scripts> should be </script>
Also your JS could look like this: http://jsbin.com/nawono/2/edit
var myMood= document.getElementById("mood");
var images=[
"smile.gif",
"frown.gif"
];
function change(){
myMood.src= images.reverse()[0];
}
setInterval(change,5000);
Ahh, to explain images.reverse()[0];, it reverses the array order and we always take out the 0 indexed key. Quite nice
The reason your code didn't work is you comparison is in appropriate. Where you have:
var images=[]
images[0]="smile.gif";
images[1]="frown.gif";
var myMood= document.getElementById("mood");
function change(){
if (myMood == images[0]) {
then myMood is a DOM element and images[0] is a string. Those two will never almost never be equal (unless the DOM element's toString methods produces exactly the same string).
You probably meant:
if (myMood.src == images[0]) {
so that you compare two strings that are more likely to be the same.
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>
I'm trying to write a javascript function that adds some DOM nodes to the document in the place it was called, like this:
...
<div>
<script type="text/javascript">
pushStuffToDOMHere(args);
</script>
</div>
...
i try to do it 'cleanly', without using node id property of the div, or innerHTML string manipulation. for that I need to know where in the document the script tag is located.
is there a way to do it?
Talking about cleanly, I don't think your approach is particularly clean. It is a much better idea to give the div a unique id and execute your javascript when the DocumentReady-event fires.
Do you have an overriding reason for doing it this way? If not the suggestion to use a unique id makes the most sense. And you can always use a library like jQuery to make this even easier for yourself.
However, the following quick test shows that if you use document.write() in the function then it writes the value into the place where the function was called from.
<html>
<head>
<script type="text/javascript">
function dosomething(arg){
document.write(arg);
}
</script>
</head>
<body>
<div>The first Div</div>
<div>The
<script type="text/javascript">
dosomething("Second");
</script>
Div
</div>
<div>The
<script type="text/javascript">
dosomething("Third");
</script>
Div
</div>
</body>
</html>
But, again the question, are you sure this is what you want to do?
Although I agree with n3rd and voted him up, I understand what you are saying that you have a specific challenge where you cannot add an id to the html divisions, unless by script.
So this would be my suggestion for inlining a script aware of its place in the DOM hierarchy, in that case:
Add an id to your script tag. (Yes, script tags can have ids, too.)
ex. <script id="specialagent" type="text/javascript">
Add one line to your inline script function that gets the script element by id.
ex. this.script = document.getElementById('specialagent');
...And another that gets the script element's parentNode.
ex. var targetEl = this.script.parentNode;
Consider restructuring your function to a self-executioning function, if you can.
Ideally it executes immediately, without the necessity for an 'onload' call.
see summary example, next.
SUMMARY EXAMPLE:
<script id="specialagent" type="text/javascript">
var callMe = function(arg1,arg2,arg3) {
this.script = document.getElementById('specialagent');
var targetEl = this.script.parentNode.nodeName=="DIV" && this.script.parentNode;
//...your node manipulation here...
}('arg1','arg2','arg3');
</script>
The following TEST code, when run, proves that the function has identified its place in the DOM, and, importantly, its parentNode. The test has division nodes with an id, only for the purpose of the test. They are not necessary for the function to identify them, other than for testing.
TEST CODE:
<html>
<head>
<title>Test In place node creation with JS</title>
</head>
<body>
<div id="one">
<h2>Child of one</h2>
<div id="two">
<h2>Child of two</h2>
<script id="specialagent" type="text/javascript">
var callMe = function(arg1,arg2,arg3) {
this.script = document.getElementById('specialagent');
var targetEl = this.script.parentNode;
/*BEGIN TEST*/
alert('this.script.id: ' + this.script.id);
alert('targetEl.nodeName: ' + targetEl.nodeName + '\ntargetEl.id: '+targetEl.id);
alert('targetEl.childNodes.length: ' + targetEl.childNodes.length);
var i = 0;
while (i < targetEl.childNodes.length) {
alert('targetEl.childNodes.'+i+'.nodeName = ' + targetEl.childNodes[i].nodeName);
++i;
}
/*END TEST - delete when done*/
//...rest of your code here...to manipulate nodes
}('arg1','arg2','etc');
</script>
</div>
</div>
</body>
</html>
Not really sure what your trying to achieve but this would pass the dom element to the function when clicked. You could then use jquery in the function to do what you wanted like so
...
<script type="text/javascript">
function pushStuffToDOMHere(element)
{
$(element).append("<p>Hello</p>"); // or whatever
}
</script>
<div onclick="pushStuffToDOMHere(this);">
</div>
...
my solution is a compbination of the (good) answers posted here:
as the function is called, it will document.write a div with a unique id.
then on document.onload that div's parent node can be easily located and appended new children.
I chose this approach because some unique restrictions: I'm not allowed to touch the HTML code other than adding script elements. really, ask my boss...
another approach that later came to mind:
function whereMI(node){
return (node.nodeName=='SCRIPT')? node : whereMI(node.lastChild);
}
var scriptNode = whereMI(document);
although, this should fail when things like fireBug append themselves as the last element in the HTML node before document is done loading.
I read that you should define your JavaScript functions in the <head> tag, but how does the location of the <script> (whether in the <head>, <body>, or any other tag) affect a JavaScript function.
Specifically, how does it affect the scope of the function and where you can call it from?
Telling people to add <SCRIPT> only in the head sounds like a reasonable thing to do, but as others have said there are many reasons why this isn't recommended or even practical - mainly speed and the way that HTML pages are generated dynamically.
This is what the HTML 4 spec says :
The SCRIPT element places a script
within a document. This element may
appear any number of times in the HEAD
or BODY of an HTML document.
And some sample HTML. Doesn't it look pretty all formatted here :)
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A document with SCRIPT</TITLE>
<META http-equiv="Content-Script-Type" content="text/tcl">
<SCRIPT type="text/vbscript" src="http://someplace.com/progs/vbcalc">
</SCRIPT>
</HEAD>
<BODY>
<SCRIPT type="text/javascript">
...some JavaScript...
</SCRIPT>
</BODY>
</HTML>
And something to look forward to in HTML 5 :
New async attribute in <SCRIPT> :
Note: There are ways [sic] a script can be
executed:
The async attribute is "true": The
script will be executed asynchrously
with the rest of the page, so the
script will be executed while the page
continues the parsing.
The async attribute is "false", but
the defer attribute is "true": The
script will be executed when the page
is finished with the parsing.
The normal rules of play still stand; don't use stuff before it's defined. :)
Also, take note that the 'put everything at the bottom' advice isn't the only rule in the book - in some cases it may not be feasible and in other cases it may make more sense to put the script elsewhere.
The main reason for putting a script at the bottom of a document is for performance, scripts, unlike other HTTP requests, do not load in parallel, meaning they'll slow down the loading of the rest of your page. Another reason for putting scripts at the bottom is so you don't have to use any 'DOM ready' functions. Since the script tag is below all elements the DOM will be ready for manipulation!
EDIT: Read this: http://developer.yahoo.com/performance/rules.html#js_bottom
One of the aspects of placement is performance. See this fine article within the YSlow discussion for why it's sometimes recommended you put them at the bottom of the document.
As for issues of scope, the usual visibility rules for Javascript (vars defined inside or outside of functions, local, global, closures, etc.) are not affected so far as I know.
Position of script tag does matter.
If you bind a Function with document Element then the document element has to be loaded first before we implement function. suppose getTeachers() is function in getTeachers.js file.
This will give you an error:
<html xmlns="http://www.w3.org/1999/xhtml">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Unit Teachers</title>
<head>
<script type="text/javascript" src="getTeachers.js"></script>
<script type="text/javascript">
document.getElementById("buttonId").onclick=function(){getResults()};
</script>
</head>
<body>
<form>
<input type = "button" id="buttonId" value = "Press for Results" /><br />
</form>
<span id="results" /></span>
</body>
</html>
It gives error before head is loaded first and it cannot find element with id specified.
The below code is correction:
<html xmlns="http://www.w3.org/1999/xhtml">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Unit Teachers</title>
<head>
<script type="text/javascript" src="getTeachers.js"></script>
</head>
<body>
<form>
<input type = "button" id="buttonId" value = "Press for Results" /><br />
</form>
<script type="text/javascript">
document.getElementById("buttonId").onclick=function(){getResults()};
</script>
<span id="results" /></span>
</body>
</html>
If your script refers to an ID on the page and the page has not been rendered (i.e. script is before HTML, or your script is executed with onload, rather then the DOM is ready) you can also get an error.
It doesn't. Most programming framework scatter scripts all throughout the page. I've only rarely seen problems because of that (and only from older browsers).
If you pull Javascripts in through XMLHttpRequest, like Diodeus said, it probably won't work. In my case, there was no error, the browser just ignores the new script(s).
I ended up using this, not terribly elegant but works for me so far:
http://zeta-puppis.com/2006/03/07/javascript-script-execution-in-innerhtml-the-revenge/
How to use execJS: http://zeta-puppis.com/2006/02/23/javascript-script-execution-in-innerhtml/
Note: Watch out for < in this line: for(var i=0;i<st.length; i++)
If you have an inline script (outside functions) located before functions it may call, you may get an error because they may not be not available yet. Not saying it is always going to happen, just that it may depending on browser type or version.
Javascript's scoping rules are similar to perl - you can call any function at the current or any higher scope level. The only restriction is that the function has to be defined at the time you call it. The position in the source is irrelevant - only the position in time matters.
You should avoid putting scripts in the <head> if possible as it slows down page display (see the link Alan posted).