Memory Heap: where objects are stored

When a program creates an object { hp: 100 }, its data needs to be stored somewhere. V8 stores objects in a memory area called the heap.

Consider how an object is created and a second reference appears:

const player = { hp: 100 };
const target = player;
target.hp = 80;
// player.hp is also 80

1. const player = { hp: 100 } creates a player object. In the interactive diagram, V8 allocates heap memory for it and stores its hp property there. The variable player receives a reference to this object.
2. const target = player reads the value of player and assigns it to target. This copies the reference: both variables now provide access to the same object. No second object is created.
3. target.hp = 80 follows the reference to the object and changes its hp property. The references themselves stay the same. As a result, player.hp also becomes 80.

The diagram shows the connections between the variables and the object. The engine determines the actual memory layout. Below, we will execute the example line by line: the object, references, and property values appear as execution proceeds.