Detecting existance of a variable

[Fabian]

How can I check whether or not a variable exists in a script? I'm
thinking in terms of

if (my variable exists) { myfunction(); }

 

[Richard Cornford]

How can I check whether or not a variable exists in a script? I'm
thinking in terms of

if (my variable exists) { myfunction(); }

if(typeof x != 'undefined'){
...
}

Is as near as you can get. But a variable that is declared but has not
yet been assigned a value will also return 'undefined' from a typeof
test. A declared variable could be said to "exist" but in reality this
is probably suitable to your problem.

Richard.

 

[KC Wong]

How can I check whether or not a variable exists in a script? I'm

thinking in terms of

if (my variable exists) { myfunction(); }

It's an ugly hack, but you can use a try...catch block to do it.

try {
var i = myVariable;
// My variable is there...
myFunction();
} catch (exception) {
// My variable is not there
}


HTH,

KC

 

[Fabian]

Richard Cornford hu kiteb:

if(typeof x != 'undefined'){
...
}

Is as near as you can get. But a variable that is declared but has not
yet been assigned a value will also return 'undefined' from a typeof
test. A declared variable could be said to "exist" but in reality this
is probably suitable to your problem.

Thanks. That did the job. I have a javascript page separated into two
files, a data file and a parser file. By checking for the existance of
the variable, it can continue to handle the older version of the data
file.