extendscript object is invalid - extendscript

Question

InDesign scripting question.
I know what need to write with var. I just try to understand what happen...
There is my script:
function myalert(s){
var w = new Window('palette')
ws = w.add('statictext',undefined,s)
w.show()
$.sleep(1000)
w.close()
}
myalert('hello')
alert(ws)
alert:
1. [Object StaticText]
2. JavaScript Error! Object is invalid...
Question: why this happen? Why error after alert? ws already deleted from memory? Then why I see alert? Not deleted? Then why I see error?

Answer 1

First myalert() executes and you see 'hello' alert.
Then myalert() finishes and ws gets deleted along with w (which is local to myalert()).
Then you try accessing ws in global scope - after it was deleted - and get the error.
See:
var w = 100 // global
function myalert(s){
var w = new Window('palette') // local (shadows 100)
ws = w.add('statictext',undefined,s) // global
w.show()
$.sleep(1000)
w.close()
alert('In myalert() w = ' + w)
alert('In myalert() ws = ' + ws)
}
myalert('hello')
alert('Global, w = ' + w)
alert('Global, ws = ' + ws)
If you don't use var, both w and ws will stay in global scope:
function myalert(s){
w = new Window('palette')
ws = w.add('statictext',undefined,s)
w.show()
$.sleep(1000)
w.close()
alert('[myalert] w = ' + w)
alert('[myalert] ws = ' + ws)
}
myalert('hello')
alert('[global] w = ' + w)
alert('[global] ws = ' + ws)
PS. You can also dump objects on console with $.writeln('ws = ' + ws)