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JavaScript undefined Property
JavaScript Global Functions
Definition and Usage
The undefined property indicates that a variable has not been assigned a value.
Browser Support
The undefined property is supported in all major browsers.
Example
Example
Test if variables are undefined:
<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>
The output of the code above will be:
t2 is undefined
Try it yourself »
JavaScript Global Functions
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