srcElement in IE = what in Netscape?

[Dan]

Hi,

When i click down with the mouse, i want to be sure that the image "myimg"
is clicked before doing something. With IE i use 'srcElement' and it works:

<IMG ID="myimg" SRC="bugs.gif" onMouseDown="downtest()">
<script>
function downtestIE()
{strid =window.event.srcElement.id
if (strid=="myimg")
{ etc ...

But how to do the same for Netscape? I tried with 'currentTarget' but get
always: 'e has no properties'
<script>
var e;
function downtest(e)
{strid=e.currentTarget
if (strid=="myimg")
{ etc ...

Any help is welcome
Dan

 

[Lasse Reichstein Nielsen]

When i click down with the mouse, i want to be sure that the image "myimg"
is clicked before doing something. With IE i use 'srcElement' and it works:

The official name is "target". Also, there is no "window.event" in
Mozilla/Netscape, that is a Microsoft invention as well.

<IMG ID="myimg" SRC="bugs.gif" onMouseDown="downtest()">

<script>

<script type="text/javascript">

The type attribute is mandatory.

function downtestIE()

Try:

function downtest(event) {
event = event || window.event; // IE doesn't pass event as argument.
var tgt = event.target || event.srcElement; // IE doesn't use .target
var strid = tgt.id;

if (strid=="myimg")
{ etc ...

/L

 

[Dan]

Thanks for replying...
I tried different ways about this and maybe you can help me understand some
differences:
1) this works ('ev' is used instead of 'event')
<IMG ID="myimg" SRC="bugs.gif" >
<script type="text/javascript">
var ev;
lap=document.getElementById("myimg")
function downtest(ev)
{
var strid = ev.target.id;
alert(strid)
}
lap.onmousedown=downtest // WHY NOT
lap.onmousedown=downtest(ev) ??
</script>

2) this works too ('event' used)
<IMG ID="myimg" SRC="bugs.gif" onMouseDown=downtest(event)>
<script type="text/javascript">
lap=document.getElementById("myimg")
function downtest(event)
{
var strid = event.target.id;
alert(strid)
}
</script>

3) this doesn't work: why can 'event' not be replaces by 'ev'? error= ev has
no properties
<IMG ID="myimg" SRC="bugs.gif" onMouseDown=downtest(ev)>
<script type="text/javascript">
var ev;
lap=document.getElementById("myimg")
function downtest(ev)
{
var strid = ev.target.id;
alert(strid)


thanks for your time
Dan

 

[Dan]

thanks

Please don't top-post.



This (global) variable declaration is not necessary. The (local) function
parameter overshadows it inside the function, and you never assign anything
to the global variable.


Why not what? It looks absolutely correct, although I would end my
sentences with a semicolon. Mostly because I find it more readable.


This is not what you want. You don't want to call the function now
and assigne the result (which is "undefined" since there is no return
statment in it) to "lap.onmousedown".

If you have both of these lines, the latter overwrites the former,
which might be why you don't see the result.


You should have quotes around the "onmousedown" attribute value,
since it contains "(" and ")". In practice, it is easier to always
put quotes around than to worry which charaters are legal and
which aren't.

You call the "downtest" function with the value of the "event"
variable. The javascript code in the onmousedown attribute value is
evaluated in a context, where "event" refers to the current event
(probably why Microsoft decided to just have one global event
variable). The *value* of the variable "event" is used as argument
to the downtest function.


The name of the function argument is irrelevant, you can call it "ev",
"event", "foo" or even "body" without affecting how this function works.
A function argument is local to the function, so
---
var x=4;
function foo(x){
x=2;
return x;
}
foo(12);
alert(x);
---
will alert "4". The variable "x" outside the function and the one inside
are two different variables, and the following is *completely* equivalent:
---
var x=4;
function foo(y){
y=2;
return y;
}
foo(12);
alert(x);
---
(in programming language theory, that is a well known concept: renaming
of "bound" variables doesn't change the behavior of the program).


Here the code "downtest(ev)" is executed in an environment where
there is a variable, called "event", referring to the current event.
The "ev" variable is the one you declare below, and it only contains
"undefined".


That means that at this point, the local variable (also called "ev")
has the value "undefined", and you can't find the property "target"
of a value that is "undefined".

/L