If a is undefined, this works:
if(window.a) {}
while this throws an error:
if(a)
Can someone explain why?
If a is undefined, this works:
if(window.a) {}
while this throws an error:
if(a)
Can someone explain why?
Share Improve this question edited Apr 13, 2011 at 16:40 Pops 30.9k37 gold badges137 silver badges153 bronze badges asked Mar 30, 2010 at 8:16 Andreas KöberleAndreas Köberle 111k58 gold badges280 silver badges307 bronze badges 01 Answer
Reset to default 10window.a is a property of window and it's undefined. a is a variable, and it's undeclared.
To use a variable, you should first declare it using the var statement. Since you didn't declare a, the interpreter raises an error. Object properties are not needed to be explicitly declared in order to use them. Crockford writes in The Good Parts:
If you attempt to extract a value from an object, and if the object does not have a member with that name, it returns the undefined value instead.