The Memory Plot of Javascript

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Execute JS code

  • Preparation before execute JS code
    • Ready Work
    • Provide API: window/ document/ setTimeout
    • Above code does not belong to JS itself
    • We call these code as runtime env
    • Once put JS code into the runtime env, it starts to execute JS code

Where is the JS code running?

 Memory

Stack and Heap

Heap and Stack

  • Red area divided into Stack and Heap
  • The data structure about a stack and heap will be talked later
  • Stack: Each data stored in order
  • Heap: Each data stored randomly

    Rules:

    • There are two data types: Object and non-object
    • Non-Object stores in the Stack
    • Object stores in the Heap
    • ’=’ operator always copy right content to left

    • Example(When the value has been changed):

      Change Value Window in memory Window in memory 2

When you need to know the structure of a function

  • use console.dir(window.Object)

What the difference between __proto__ and prototype?

  • Both of then store the address of the prototype
  • However, prototype only exists in functions
  • __proto__ exists in every new object

Important Picture Note

Change Value