What was the rationale behind having the receiver in functions default to the global object?

Question

In early versions of JavaScript, what was the rationale behind having the receiver (aka context) default to the global object?

function a() {
  console.log(this); // window
}

Answer 1

Brendan Eich answered:

So that top-level functions (the only kind in first release) can act as window or frame (later, iframe) methods. Still used.

JS jargon nit: "receiver" is the standard OO term in languages that influenced JS, rather than highly-overloaded "context".

Question posed to Brendan Eich:

So ES1 did not have methods? (cf ur comment on top level fns)

Brendan Eich:

No, JS1 in '95 (no "ES" then) had methods via function-valued properties, but all functions were top level. ES1 standardized.

ES3 in '99 added function expressions & nested functions (closures), which I didn't have time to implement in those 10 days.

To go back to orig q: in window w, function m(){} makes w.m() callable from other reachable windows/frames with this == w.