Objects and this

Key points

1. 1this is set by the call: obj.method() gives obj, a detached method gets undefined in strict code or the global object otherwise.
2. 2call and apply run a function now with a chosen this (apply takes an array of arguments); bind returns a new function.
3. 3Spread and Object.assign copy only the top level. Nested objects stay shared; Object.assign also changes its first argument.
4. 4Object.create links a new object to a prototype. Changes to the prototype are seen later, and Object.keys lists only own properties.
5. 5seal blocks adding and deleting, freeze also blocks changes, and both are shallow. defineProperty flags default to false.