Global environment record object and declarative with Example

In JavaScript, the global environment record is a concept related to how variable and function declarations are handled within the global scope. The global environment record is essentially a data structure that stores global variables and functions. It's part of the global execution context, which is created when a JavaScript program starts running.

Global Environment Record

The global environment record is responsible for:

1. Binding Global Variables: It keeps track of all global variables and functions declared using var, let, const, and function declarations.

2. Handling Global Object: In browsers, the global object is window, and in Node.js, it's global. The global environment record associates global variables with this global object.

3. Declarative vs. Imperative Binding: In the global environment, bindings can be created both declaratively (e.g., using var, let, const, and function declarations) and imperatively (e.g., by assigning properties directly on the global object).

Example of Global Environment Record

Consider the following JavaScript code:

javascript

// Global variable declaration
var globalVar = 'I am a global variable';

// Function declaration
function globalFunc() {
    console.log('I am a global function');
}

// Block scope variable with let
let blockVar = 'I am block scoped';

// Block scope constant with const
const blockConst = 'I am block scoped constant';

// Imperative global assignment
window.imperativeVar = 'I am an imperative global variable'; // in browsers
global.imperativeVar = 'I am an imperative global variable'; // in Node.js

How It Works

1. Global Variables and Functions: globalVar and globalFunc are declared globally. They are stored in the global environment record and can be accessed throughout the script.

2. Block Scope Variables: blockVar and blockConst are declared with let and const, respectively. They are block-scoped and will not be part of the global environment record but are scoped to the block they are declared in.

3. Imperative Assignment: The lines where imperativeVar is assigned to the global object (window in browsers or global in Node.js) demonstrate imperative global binding. This explicitly adds properties to the global object.

In summary, the global environment record maintains a reference to global variables and functions and manages their declarations and assignments. It ensures that these global bindings are accessible throughout the script execution.