splicein DefineListt removing undefined values in source array

[mikemitchel]

How often can you reproduce it?

• Always
• Sometimes
• Rarely
• Unable
• I didn’t try

Description:
If the source array for a new DefineList contains only values of undefined at each index, it passes the allSame test here when calling splice:

can-define/list/list.js

Lines 294 to 297 in ea827f8

	// Now lets check if anything will change
	if (this[i + index] !== args[listIndex]) {
	allSame = false;
	}

as it thinks nothing will change, and ends up returning a DefineList of length 0. As long as at least one element in the source array is not undefined it works as expected.

var undefinedList = new DefineList([undefined, undefined])
console.log('so much empty', undefinedList.length) //=> 0

See this codepen example:
https://codepen.io/mikemitchel/pen/eYOMwmE

Expected results:
I expected in the first example of the codepen to have a DefineList of length 2, with the value at each index being undefined.

Environment:

Software	Version
can-define version	"^2.7.10"
Browser	Chrome Version 76.0.3809.132 (Official Build) (64-bit)
Operating system	MacOS 10.14.6 (18G95)