Today, one of my major misconceptions regarding the handling of “undefined” variables in JavaScript got corrected.
I had to call a function if that function was loaded, else show an alert window as
if (foo) {
foo();
} else {
alert("something");
}
In the scenario where foo was yet to be loaded, I got an error saying “foo is not defined”. I was a bit taken back as until today I was under the misconception that in JavaScript if a variable is not defined (not not initialized..the pun is not intentional ;)) and I use it in a condition evaluation, it evaluates to false. This was because usually I do not do it as above. I usually check as to whether a variable is defined or not using the typeof function as below.
if (typeof foo != 'undefined') {
foo();
} else {
alert("something");
}
So, moral of the story. In JavaScript, I can use a variable in condition evaluation only if it has been defined (does not matter whether it has been initialized or not).
