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Creation Phase

Creation Phase

Introduction

The Creation Phase (also called Memory Allocation Phase) is the first of two phases in every execution context. During this phase, JavaScript sets up memory space for variables and functions before any code is executed.

What Happens

Create the LexicalEnvironment (scope)
Create the VariableEnvironment
Set up the this binding
Allocate memory for variables (initialized to undefined)
Store function declarations (fully hoisted)

Example

// What you write:
console.log(myVar);  // undefined
var myVar = 10;

// Behind the scenes (creation phase):
// var myVar; → allocated, initialized to undefined
// Then execution phase runs:
// console.log(myVar); → undefined
// myVar = 10; → assigned

Hoisting During Creation

// During creation phase:
var a;              // allocated, set to undefined
function greet() {} // fully stored in memory
let b;              // allocated, NOT initialized (TDZ)
const c;            // allocated, NOT initialized (TDZ)

The this Binding

// Global context: this = global object
console.log(this); // window (browser)

// Function context: this depends on how the function is called
function showThis() {
  console.log(this);
}

Summary

Creation phase runs before any code executes
Variables with var are initialized to undefined
Function declarations are fully hoisted
let and const are allocated but not initialized
this binding is set up

Further Reading