Is it possible to define a global variable in a JavaScript function?
I want use the trailimage
variable (declared in the makeObj
function) in other functions.
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title></title>
<script type="text/javascript">
var offsetfrommouse = [10, -20];
var displayduration = 0;
var obj_selected = 0;
function makeObj(address) {
**var trailimage = [address, 50, 50];**
document.write('<img id="trailimageid" src="' + trailimage[0] + '" border="0" style=" position: absolute; visibility:visible; left: 0px; top: 0px; width: ' + trailimage[1] + 'px; height: ' + trailimage[2] + 'px">');
obj_selected = 1;
}
function truebody() {
return (!window.opera && document.compatMode && document.compatMode != "BackCompat") ? document.documentElement : document.body;
}
function hidetrail() {
var x = document.getElementById("trailimageid").style;
x.visibility = "hidden";
document.onmousemove = "";
}
function followmouse(e) {
var xcoord = offsetfrommouse[0];
var ycoord = offsetfrommouse[1];
var x = document.getElementById("trailimageid").style;
if (typeof e != "undefined") {
xcoord += e.pageX;
ycoord += e.pageY;
}
else if (typeof window.event != "undefined") {
xcoord += truebody().scrollLeft + event.clientX;
ycoord += truebody().scrollTop + event.clientY;
}
var docwidth = 1395;
var docheight = 676;
if (xcoord + trailimage[1] + 3 > docwidth || ycoord + trailimage[2] > docheight) {
x.display = "none";
alert("inja");
}
else
x.display = "";
x.left = xcoord + "px";
x.top = ycoord + "px";
}
if (obj_selected = 1) {
alert("obj_selected = true");
document.onmousemove = followmouse;
if (displayduration > 0)
setTimeout("hidetrail()", displayduration * 1000);
}
</script>
</head>
<body>
<form id="form1" runat="server">
<img alt="" id="house" src="Pictures/sides/right.gif" style="z-index: 1; left: 372px;
top: 219px; position: absolute; height: 138px; width: 120px" onclick="javascript:makeObj('Pictures/sides/sides-not-clicked.gif');" />
</form>
</body>
</html>
Classic example:
Modern, safe example following best practice by using an IIFE:
Nowadays, there's also the option of using the WebStorage API
or
Performancewise, I'm not sure whether it is noticeably slower than storing values in variables.
Widespread browser support as stated on Can I use...
I realize there is probably a lot of syntax errors in this but its the general idea... Thanks so much LayZee for pointing this out... You can find what a local and session Storage is at http://www.w3schools.com/html/html5_webstorage.asp. I have needed the same thing for my code and this was a really good idea.
UPDATE1: If you read the comments there's a nice discussion around this particular naming convention.
UPDATE2: It seems that since my answer has been posted the naming convention has gotten more formal. People who teach, write books etc. speak about
var
declaration, andfunction
declaration.UPDATE3: Here is the additional wikipedia post that supports my point: http://en.wikipedia.org/wiki/Declaration_(computer_programming)#Declarations_and_Definitions
...and to answer the main question. DECLARE variable before your function. This will work and it will comply to the good practice of declaring your variables at the top of the scope :)
if you are making a startup function, you can define global functions and variables in such way:
Because the function is invoked globally with this argument, this is global scope here. So, the something should be a global thing.
It is very simple define the trailimage variable outside the function and set its value in makeObj function. Now you can access its value from anywhere.
Here is a sample code that might can be helful.
Here I found a nice answer How-can-one-declare-a-global-variable-in-JavaScript