I couldn't resist - the other answers are undoubtedly true, but you really can't walk past the following code:

var aﾠ = 1; var a = 2; var ﾠa = 3; if(aﾠ==1 && a== 2 &&ﾠa==3) { console.log("Why hello there!") }

Note the weird spacing in the if statement (that I copied from your question). It is the half-width Hangul (that's Korean for those not familiar) which is an Unicode space character that is not interpreted by ECMA script as a space character - this means that it is a valid character for an identifier. Therefore there are three completely different variables, one with the Hangul after the a, one with it before and the last one with just a. Replacing the space with _ for readability, the same code would look like this:

var a_ = 1; var a = 2; var _a = 3; if(a_==1 && a== 2 &&_a==3) { console.log("Why hello there!") }

Check out the validation on Mathias' variable name validator. If that weird spacing was actually included in their question, I feel sure that it's a hint for this kind of answer.

Don't do this. Seriously.

Edit: It has come to my attention that (although not allowed to start a variable) the Zero-width joiner and Zero-width non-joiner characters are also permitted in variable names - see Obfuscating JavaScript with zero-width characters - pros and cons?.

This would look like the following: