Change the minified version of `undefined` to `1..u`

This returns undefined, and it’s two bytes shorter than void 0 (it’s also 5 bytes shorter than undefined). The . operator has a higher priority than the void operator, so it’s safe. A plugin could also replace all instances of void 0 in other code with 1..u.

[loganfsmyth]

Doesn’t seem like a good idea since everything would break if someone did Object.prototype.u = 4. We could hoist the definition with a var u = void 0; at the top of the file if there are more than a couple references to undefined though.

[ashsearle]

A little brain-dump for @loganfsmyth’s hoisting suggestion…

Remember that undefined is the default value for a variable, so this could be shorter at var u; or let u; (although I guess it would be more robust to use const u = void 0)

Also, there may be opportunities to piggy-back on a list of other variables declared, so could be as little as 2 additional characters. e.g. if a and b are already defined in a var a,b; declaration, then we only add ,u to get var a,b,u;

Or, if you want to use const for robustness, you place the const immediately after an uninitialised variable declaration: var a,b;const u=a;