Extend with respect for undefined
xtendr is a basic utility library which allows you to extend an object by
appending all of the properties from each object in a list. When there are
identical properties, the right-most property that is not undefiend
takes presedence, except where all values are undefined.
An undefined value will not overwrite a value, because the object property as the name describes, is actually undefined.
Furthermore, the resuling object will have all keys set, even if the only value for that key is undefined. The preserves your right to define the enumerable keys, but to respect undefined values where you do not wish to override.
xtendr patches xtend to respect the meaning of undefined vs null
var extend = require("xtendr")
// extend returns a new object. Does not mutate arguments
var combination = extend({
a: "a"
}, {
a: undefined,
b: "b",
c: undefined
})
// { a: "a", b: "b", c: undefined }