apply(this_obj, params_array)

Allows you to call another function while overwriting its this value. The first parameter that apply() accepts is the object to be bound to this inside the function and the second is an array of parameters to be passed to the function being called.

function whatIsIt(){
  return this.toString();
}
>>> var myObj = {};
>>> whatIsIt.apply(myObj);

"[object Object]"

>>> whatIsIt.apply(window);

"[object Window]"

call(this_obj, p1, p2, p3, ...)

Same as apply() but accepts parameters one by one, as opposed to as one array.

length

The number of parameters the function expects.

>>> alert.length

1

>>> parseInt.length

2