JavaScript has three types of execution contexts: global, function, and eval. Each is created at different times and serves a different purpose.

Created when the JavaScript script first runs:

// This runs in the global execution context
const globalVar = 'I am global';

function outer() {
  // Function execution context
}

• Only one global context exists
• It’s the default context
• In browsers: this = window
• In Node.js: this = global
• Remains active until the program ends

Created every time a function is called (not defined):

function first() {
  // Function EC for first()
  function second() {
    // Function EC for second()
  }
  second();
}

first();
// Creates: Global EC → first() EC → second() EC

• Each function call creates a new context
• Multiple function contexts can exist (stacked)
• Each has its own variable environment and this binding

Created when code is executed inside eval():

eval('var x = 10;'); // Creates an eval execution context

• Rarely used (and discouraged)
• Has its own scope
• Can access the enclosing scope

flowchart LR
    A["Script Starts"] --> B["Global EC Created"]
    B --> C["Function Called"]
    C --> D["Function EC Created"]
    D --> E["Function Returns"]
    E --> F["Function EC Destroyed"]
    F --> G["More Functions?"]
    G -->|Yes| C
    G -->|No| H["Program Ends"]
    H --> I["Global EC Destroyed"]

• MDN: Execution Context
• Next: Creation Phase