Question

What does this mean in var definition:

var array = array || [];

… and next two parts of javascript are equal each other?

var array = array || [];
array.push([1],[2]);
array.push([3]);

=

var array = array.push([1],[2],[3]) || [];

?

Answer 1

It means that if array is a falsy value (undefined, null etc.) – the value that will be assigned to the var array is an empty array – [];

EDIT:

the second part of your question – no these are not equivalent.

For instance, when array is undefined:

var array = array.push([1],[2],[3]) || [];

this will throw an exception.

This:

var array = array || [];
array.push([1],[2]);
array.push([3]);

will not.