How to compare variables to undefined, if I don’t know whether they exist?
37735
How can I check for "undefined" in JavaScript?
151869
What's the scope of a variable initialized in an if statement?
125415
Why is undefined == undefined but NaN != NaN?
78285
How to check for equals? (0 == i) or (i == 0)
141197
In JavaScript, is there an easier way to check if a property of a property exists?
105797
Why can't we define a variable inside an if statement?
9266
Why does Chrome debugger think closed local variable is undefined?
53586
How can I type-check variables in Python?
91340
Testing if a variable is empty in a shell script
70566
How do I check if an object has a key in JavaScript?
89549
Can anyone explain this 'variable does not exist error'?
3528
How to check if a variable is the same as at least one of two other variables?
5377
Is there a standard function to check for null, undefined, or blank variables in JavaScript?
317
What is the scope of variables in JavaScript?
123815
How to find JavaScript variable by its name
53203
Checking for undefined
96317
How to check type of variable in Java?