Q1321 Can you explain the scope of global and local variables in relation to functions?
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Q1321 Can you explain the scope of global and local variables in relation to functions?
Take for example the following code:
<script language="JavaScript"><!--
// declare global variable
var variable1;
// declare and initialise global variables
var variable2 = '2';
variable3 = '3';
document.write('1 = ' + variable1 + '<br>'); // 1 = undefined
document.write('2 = ' + variable2 + '<br>'); // 2 = 2
document.write('3 = ' + variable3 + '<br>'); // 3 = 3
document.write('6 = ' + variable6 + '<br>'); // 6 = undefined
document.write('6 = ' + variable6 + '<br>'); // JavaScript Error: variable6 is not defined.
function myFunction() {
// declare and initialise local variables
var variable1 = '1 amended';
var variable2;
// initialise global variable value
variable3 = '3 amended';
// declare local variable
var variable4;
// declare and initialise local variable
var variable5 = '5';
// declare and initialise global variable
variable6 = '6';
document.write('1 = ' + variable1 + '<br>'); // 1 = 1 amended
document.write('2 = ' + variable2 + '<br>'); // 2 = undefined
document.write('3 = ' + variable3 + '<br>'); // 3 = 3 amended
document.write('4 = ' + variable4 + '<br>'); // 4 = undefined
document.write('5 = ' + variable5 + '<br>'); // 5 = 5
document.write('6 = ' + variable6 + '<br>'); // 6 = 6
document.write('7 = ' + variable7 + '<br>'); // 7 = undefined
document.write('8 = ' + variable8 + '<br>'); // 8 = undefined
// declare local variable
var variable7;
// declare and initialise local variable
var variable8 = '8';
document.write('8 = ' + variable8 + '<br>'); // 8 = 8
document.write('9 = ' + variable9 + '<br>'); // JavaScript Error: variable9 is not defined.
}
myFunction();
document.write('1 = ' + variable1 + '<br>'); // 1 = undefined
document.write('2 = ' + variable2 + '<br>'); // 2 = 2
document.write('3 = ' + variable3 + '<br>'); // 3 = 3 amended
document.write('4 = ' + variable4 + '<br>'); // JavaScript Error: variable4 is not defined.
document.write('5 = ' + variable5 + '<br>'); // JavaScript Error: variable5 is not defined.
document.write('6 = ' + variable6 + '<br>'); // 6 = 6
document.write('7 = ' + variable7 + '<br>'); // JavaScript Error: variable7 is not defined.
document.write('8 = ' + variable8 + '<br>'); // JavaScript Error: variable8 is not defined.
document.write('9 = ' + variable9 + '<br>'); // JavaScript Error: variable9 is not defined.
//--></script>
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If we declare but not initalise a variable outside a function it
should be global in scope, but undefined until the point at which it
is initialised - e.g. variable1.
If we declare (with or without the var keyword) and initialise a
variable outside a function it should be global in scope and
accessible immediately - e.g. variable2 and variable3
If we declare (and optionally initialise) a variable with the var
keyword inside a function, even though a global variable of the same
name exists outside of the function, then it should be local in scope
and not effect the value of the global variable - e.g. variable1 and
variable2.
If we declare and initialise a variable without the var keyword inside
a function, if a global variable of the same name exists outside of
the function, then it should effect the value of the global variable,
and still remain global - e.g. variable3.
If we declare but not initalise a variable with the var keyword inside
a function it should be local in scope, but undefined across the
complete function until the point at which it is initialised -
e.g. variable4 and variable7.
If we declare and initialise a a variable with the var keyword inside
a function it should be local in scope and accessible immediately -
e.g. variable5.
If we declare and initialise a variable without the var keyword inside
a function it should be global in scope, but not accessible prior to
the function being invoked - e.g. variable6.
If we declare and initalise a variable with the var keyword inside
a function it should be local in scope, but undefined across the
complete function until the point at which it is initialised -
e.g. variable8.
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