Forum Moderators: open
<!--<HTML>
<HEAD>
<TITLE>imagesByButtos</TITLE>
<SCRIPT TYPE="text/javascript">
var pr1= new Image();
pr1.scr="images1.jpeg"
var pr2= new Image();
pr2.scr="images2.jpeg"
var pr3= new Image();
pr3.scr="images3.jpeg"
var pr4= new Image();
pr4.scr="images4.jpeg"
var pr5= new Image();
pr5.scr="images5.jpeg"
var pr6= new Image();
pr6.scr="images6.jpeg"
var people=new Array( pr1.scr, pr2.scr, pr3.scr, pr4.scr, pr5.scr, pr6.scr);
function chImage(imageName, arrayName, elementNum)
{
document.images[imageName].src = arrayName[elementNum ];
}
</SCRIPT>
</HEAD>
<!-- <BODY onload="chImage( chpeople, people,5)"> can't pass chpeople to function this way -->
<!--<BODY onload="chImage( chpeople, people,5)"> can pass 'chpeople' to function this way -->
<BODY onload="chImage(0, people,5)"> <!-- can pass zero to function this way -->
<IMG NAME = "chpeople" SRC="images1.jpeg" BORDER="0" ALIGN="bottom" ALT="changing people"><BR>
</BODY>
</HTML>-->
However when I pass at the argument of the image object name without quotes my function fails.
This is because the image name is a name - it is not a global variable holding the image of that name. Some browsers may, in the past, have flatted element names and ids into globals (IE still does with ids) but it's not a reliable technique.
You are referencing image objects via the document.images collection. Like all collections, the member elements can be referenced by source index, id or name (if an image, form element or frame) so you need
document.images["_name_"]
//or
document.images[_index_]
If you don't use quotes on the string, then javascript sees it as a variable, and then turn that into a string for the array access, so you effectively get:
document.images["undefined"]
I have read that the default data type for JavaScript is strings.
There is no default data type.
--------------------------------------
function chImage(imageName, array, elementNum)
{
document.images[imageName].src = arrayName[elementNum ];
}...
chImage('chpeople', people, 5)"> ');
//
--------- easier?---------------------
//
function chImage(imageElmName, src )
{
document.images[imageName].src = src;
}...
chImage('chpeople', people[5] )"> ');
//
---------------------------------------
//
Serious typographical error.
You are using scr not src. It still works because objects can have arbitrary properties added to them. However, the preloading won't happen.
[b]A)[/b] myFunction[red]([/red][green]"hello"[/green][red])[/red][b]B)[/b] myFunction[red]([/red]hello[red])[/red]
In case (A) we're passing a string to the function. It is string "literal", that is to say it is nothing more than what it contains.
In case (B) we're passing a variable (the bread & butter of all programming). What value that variable has depends on the value we have given it, and in what scope the statement is executing in
- there may be a global variable,
hellohelloIn the above, we have neither declared nor initialised
helloUnder no circumstances, will
hello"hello"However, it is possible, in various ways, to use the string,
"hello"helloSummary:
A string literal is a string literal; a variable name is a variable name.
You can set, access or change the properties of any (touch wood) object that you will come across in Javascript in 2 ways:
To demo this, I'll create a Javascript Object-type object. This is just to make things easy, but the concept applies to all objects, including document elements.
// create an object with a property¦value
var obj1 = {bananas: 1};alert( obj1.bananas );
alert( obj1["bananas"]);
// or even
alert(ob1["bana"+"nas"]);
Object properties are actually stored internally as strings. This is why the following statement, from your code, works:
document.images[imageName].src = ...If we want to reference an image with the name, "image1", then we can:
document.images.image1;
//or
document.images["image1"];
// or,
// if we have a variable, imageName = "image1";
document.images[imageName];
// but this will not work
// (a common mistake)
document.images.imageName;In PHP, you can access an array member without using quotes:
$myArray[bananas]
You'll get away with a warning. The environment in PHP is different, because PHP knows you are not expecting the value of a variable,
$bananas$In JS, the only property access that can be made without quotes (optional) is, as you know, numerical index:
myArray[5]
