Question

var a = [1,4,5]; var e = a.length--; 

Here e variable will contain 5. But if I do:

var e = a.length-=1; 

Here e will contain 2 the number of elements array.
So the first is a language ‘tip’ to simulate a pop() array methods?

In the language syntax doing:

a-- 

or

a-=1 

is semantically the same.

Answer 1

var a = [1, 4, 5]; var e = a.length--; 

is the same as

var a = [1, 4, 5]; var e = a.length; a.length = a.length - 1; 

whereas

 var a = [1, 4, 5];  var e = a.length -= 1; 

is the same as

var a = [1, 4, 5]; a.length = a.length - 1; var e = a.length; 

and

var a = [1, 4, 5]; var e = --a.length; 

In other words: x– returns the value before decreasing whereas –x (and x -= 1) returns the value after decreasing. All these code snippets pop the last element off the array a.

Note that in the first example, e = a.length--, e will have the value 3, not 5, therefore it is not the same as a.pop().