I'm not sure of the terminology to search for an answer to this. Given:
this.snake = [{x: 0, y: 0}];
var curhead = this.snake[0];
Does curhead contain a copy of the dictionary(?) at snake[0] or a direct reference to it?
4 Answers
JavaScript always copies by value.
Objects in JavaScript, including Arrays, are only ever accessed by reference though. (i.e. foo = [] generates an array and assigns a reference to it to foo).
So you will get a copy of the first value in the array, which is a reference to the object.
This is distinct from being a reference to the first value in the array.
Given:
var array = [ { value: 1 } ];
var reference = array[0];
array.unshift( { value: 2 } );
If reference was a reference to the first value in the array, then by changing the first value it would point to the object with value : 2.
Since it is a copy of the value, it continues to be a reference to the object with value : 1 (which is now the second value in the array).
Comments
It is an array of objects with only one element. So
this.snake[0]
Will contain a reference to {x: 0, y: 0}.
Paras
Comments
Now curHead and snake[0] refers to the exact same memory location . Try changing a value in curHead it will change snake[0] as well
curhead.x = 1
console.log(curhead)
//Object {x: 1, y: 0}
console.log(this.snake)
//[{x: 1, y: 0}]
Fun things happen when you try to assign a completely new object to curhead , lets say curhead = 'hi' . Then javaScript will create a new heap space for curhead and this.snake will be unchanged to its value {x: 1, y: 0}
curheadwill have a reference.