Function execution context in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a function execution context in JavaScript?

It is the environment where a function runs. It stores information like variables, parameters, and the value of this while the function executes.

intermediate

What are the three main parts of a function execution context?

1. Variable Environment (stores variables and parameters)
2. Scope Chain (links to outer contexts)
3. this value (context of the function call)

beginner

When is a function execution context created?

It is created every time a function is called, before the function code runs, and destroyed after the function finishes.

intermediate

How does the scope chain affect variable access inside a function?

The scope chain lets the function access variables from its own context and from outer contexts, like the global scope or parent functions.

advanced

What is the value of this inside a function execution context?

It depends on how the function is called. For example, in a regular function call, this is undefined in strict mode or the global object otherwise. In methods, this is the object owning the method.

When is a new function execution context created in JavaScript?

A Every time a function is called

B Only once when the function is defined

C When the script loads

D When the browser refreshes

A new execution context is created each time a function is called to keep track of its variables and state.

Which part of the function execution context stores the function's parameters and local variables?

A Variable Environment

B Scope Chain

C <code>this</code> value

D Call Stack

The Variable Environment holds the function's parameters and local variables.

What does the scope chain in a function execution context do?

A Defines the value of <code>this</code>

B Stores the function's code

C Links to outer variable environments for variable lookup

D Manages asynchronous calls

The scope chain connects the current context to outer contexts to find variables.

What is the value of this inside a regular function call in strict mode?

A The global object

B The object owning the function

C The function itself

D Undefined

In strict mode, this is undefined in regular function calls.

What happens to a function execution context after the function finishes running?

A It stays in memory forever

B It is destroyed and removed from the call stack

C It becomes global context

D It pauses until called again

After the function finishes, its execution context is removed from the call stack and destroyed.

Explain what a function execution context is and what it contains.

Think about what the function needs to remember while it runs.

Describe how the scope chain works inside a function execution context.

Imagine looking for a variable inside nested boxes.

Practice

1. What does the function execution context in JavaScript primarily keep track of?

easy

A. Variables and parameters inside the function

B. The browser window size

C. The user's keyboard input globally

D. The network requests made by the page

Solution

1. Step 1: Understand what execution context means

   The function execution context is created when a function runs and it keeps track of what happens inside that function.

2. Step 2: Identify what is tracked inside the function

   It specifically keeps track of variables and parameters declared or passed inside the function.

3. Final Answer:

   Variables and parameters inside the function -> Option A

4. Quick Check:

   Execution context tracks variables and parameters [OK]

Hint: Execution context tracks function's own variables and parameters [OK]

Common Mistakes:

• Thinking it tracks global browser info
• Confusing with event listeners
• Assuming it tracks network requests

2. Which of the following is the correct way to define a function in JavaScript that creates a new execution context when called?

easy

A. var greet = 'Hi';

B. function greet() { console.log('Hi'); }

C. console.log('Hi');

D. if (true) { console.log('Hi'); }

Solution

1. Step 1: Identify function declaration syntax

   Only the syntax starting with the keyword function defines a function that creates an execution context when called.

2. Step 2: Check other options

   Options B, C, and D do not define functions; they are variable assignment or direct statements.

3. Final Answer:

   function greet() { console.log('Hi'); } -> Option B

4. Quick Check:

   Function declaration uses function keyword [OK]

Hint: Look for the 'function' keyword to define a function [OK]

Common Mistakes:

• Confusing variable assignment with function definition
• Thinking console.log alone defines a function
• Using if statement as a function

3. What will be the output of the following code?

function test() {
  let x = 5;
  return x + 3;
}
console.log(test());

medium

A. undefined

B. 5

C. 8

D. Error

Solution

1. Step 1: Analyze the function body

   The function test declares a variable x with value 5 inside its execution context.

2. Step 2: Calculate the return value

   The function returns x + 3, which is 5 + 3 = 8.

3. Final Answer:

   8 -> Option C

4. Quick Check:

   Return value is 5 + 3 = 8 [OK]

Hint: Add local variable and return value inside function [OK]

Common Mistakes:

• Confusing return value with variable value
• Expecting undefined because of missing global variable
• Thinking function does not return anything

4. Identify the error in the following code related to function execution context:

function add() {
  console.log(sum);
  let sum = 10 + 5;
}
add();

medium

A. TypeError because sum is not a function

B. No error, outputs 15

C. SyntaxError due to missing return statement

D. ReferenceError because 'sum' is used before declaration

Solution

1. Step 1: Understand variable hoisting with let

   Variables declared with let are not hoisted like var. Accessing them before declaration causes ReferenceError.

2. Step 2: Check the console.log usage

   The code tries to log sum before it is declared, causing ReferenceError.

3. Final Answer:

   ReferenceError because 'sum' is used before declaration -> Option D

4. Quick Check:

   Using let variable before declaration causes ReferenceError [OK]

Hint: Don't access let variables before declaration inside function [OK]

Common Mistakes:

• Assuming let variables are hoisted like var
• Expecting output 15 without error
• Confusing ReferenceError with SyntaxError

5. Consider this code:

function outer() {
  let a = 10;
  function inner() {
    let b = 20;
    return a + b;
  }
  return inner();
}
console.log(outer());

What does this example demonstrate about function execution contexts?

hard

A. Inner function can access variables of outer function's execution context

B. Inner function cannot access outer function variables

C. Outer function loses its execution context after returning

D. Variables declared in inner function are global

Solution

1. Step 1: Understand nested function execution contexts

   The inner function creates its own execution context but can access variables from the outer function's context due to closure.

2. Step 2: Analyze the return value

   The inner function returns a + b where a is from outer context and b is local, showing access to outer variables.

3. Final Answer:

   Inner function can access variables of outer function's execution context -> Option A

4. Quick Check:

   Closures allow inner functions to access outer variables [OK]

Hint: Inner functions access outer variables via closure [OK]

Common Mistakes:

• Thinking inner function variables are global
• Assuming outer context is lost immediately
• Believing inner cannot access outer variables