You'll be enrolled at LMU Munich â Germany's #1 ranked university, take language courses at JYM, and design your own program of study.
Undefined is defined. Define means to set the limits, explain. So, undefine means not to set limits or not to explain.
x === undefined will only work if the variable has actually been declared with var x (but not assigned a value). Therefore it is safer to use window.x which will not result in an error if the variable hasn't been declared. Use the === compare operator to check whether the variable is really boolean false.