variable === undefined vs. typeof variable === “undefined”

Question

The jQuery Core Style Guidelines suggest two different ways to check whether a variable is defined.

• Global Variables: typeof variable === "undefined&

Answer 1

Who is interested in the performance gain of variable === undefined, may take a look here, but it seems to be a chrome optimization only.

• http://jsperf.com/type-of-undefined-vs-undefined/30
• http://jsperf.com/type-of-undefined-vs-undefined