JavaScript undefined property
JavaScript Global Functions Definition and Usage
undefined property is used to store the JavaScript undefined value.
Browser Support
All major browsers support undefined property
Examples
Examples
Determine whether a variable is defined:
<script>
var t1="";
var t2;
if (t1===undefined)
{
alert("t1 is undefined");
}
if (t2===undefined)
{
alert("t2 is undefined");
}
</script>
var t1="";
var t2;
if (t1===undefined)
{
alert("t1 is undefined");
}
if (t2===undefined)
{
alert("t2 is undefined");
}
</script>
Examples of the above output:
t2 is undefined
try it"
JavaScript Global Functions