this in global scope in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to log the global this value in a browser environment.

Javascript

console.log([1]);

Drag options to blanks, or click blank then click option'

Aself

Bthis

Cwindow

DglobalThis

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'this' directly in strict mode returns undefined.

Using 'window' only works in browsers, not in Node.js.

In modern JavaScript, globalThis is the standard way to access the global object in any environment.

2fill in blank

medium

Complete the code to check if 'this' in the global scope equals the global object.

Javascript

console.log(this === [1]);

Drag options to blanks, or click blank then click option'

Aself

Bwindow

CglobalThis

Dglobal

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'global' which is Node.js specific.

Using 'window' which is browser specific.

this in the global scope equals globalThis in non-strict mode.

3fill in blank

hard

Fix the error in the code to correctly log the global object using 'this' in a function.

Javascript

function showGlobal() {
  'use strict';
  console.log([1]);
}
showGlobal();

Drag options to blanks, or click blank then click option'

AglobalThis

Bthis

Cwindow

Dself

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'this' inside strict mode function returns undefined.

Using 'window' which may not exist in all environments.

In strict mode, this inside a function is undefined, so use globalThis to access the global object.

4fill in blank

hard

Fill both blanks to create a function that returns true if 'this' in global scope equals the global object.

Javascript

function checkGlobal() {
  return this === [1] || this === [2];
}
console.log(checkGlobal());

Drag options to blanks, or click blank then click option'

AglobalThis

Bwindow

Cself

Dglobal

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'global' which is Node.js specific.

Using 'self' which is less common.

This function checks if this is either globalThis or window, covering most browser environments.

5fill in blank

hard

Fill all three blanks to create an arrow function that returns the global object using 'this' and fallback options.

Javascript

const getGlobal = () => [1] || [2] || [3];
console.log(getGlobal());

Drag options to blanks, or click blank then click option'

AglobalThis

Bwindow

Cself

Dthis

Attempts:

3 left

💡 Hint

Common Mistakes

Using only 'this' which may be undefined in arrow functions.

Not providing fallback options.

Arrow functions don't have their own this, so fallback to window or self to get the global object in browsers.

Practice

1. In JavaScript, what does this refer to when used in the global scope (outside any function) in a browser environment?

easy

A. The document object

B. The current function

C. The global object, which is window in browsers

D. Undefined

Solution

1. Step 1: Understand global scope context

   In the global scope, this refers to the global object in JavaScript.

2. Step 2: Identify the global object in browsers

   In browsers, the global object is window, so this points to window.

3. Final Answer:

   The global object, which is window in browsers -> Option C

4. Quick Check:

   this in global scope = window [OK]

Hint: Remember: global this is window in browsers [OK]

Common Mistakes:

• Thinking this is undefined in global scope by default
• Confusing this with the current function
• Assuming this points to document

2. Which of the following is the correct way to check if this in the global scope refers to the window object?

easy

A. console.log(this === document);

B. console.log(this === window);

C. console.log(this === global);

D. console.log(this === null);

Solution

1. Step 1: Recall global this in browsers

   In the browser global scope, this points to the window object.

2. Step 2: Compare this with window

   Using this === window returns true if this is the global object.

3. Final Answer:

   console.log(this === window); -> Option B

4. Quick Check:

   this === window is true in global scope [OK]

Hint: Check this === window to confirm global this [OK]

Common Mistakes:

• Using document instead of window
• Using global which is Node.js specific
• Comparing this to null

3. What will be the output of the following code in a browser's global scope?

console.log(this === window);
'use strict';
console.log(this);

medium

A. true and then global object

B. true and then undefined

C. false and then window object

D. true and then window object

Solution

1. Step 1: Evaluate first console.log before strict mode

   Before 'use strict', this in global scope equals window, so this === window is true.

2. Step 2: Evaluate second console.log after strict mode

   Strict mode affects this inside functions, but in global scope this still points to window, so it logs the window object.

3. Final Answer:

   true and then window object -> Option D

4. Quick Check:

   Global this = window even with strict mode [OK]

Hint: Strict mode doesn't change global this in browsers [OK]

Common Mistakes:

• Assuming this becomes undefined in global scope with strict mode
• Confusing strict mode effects inside functions vs global scope
• Thinking this equals global in browsers

4. Consider this code snippet:

'use strict';
function checkThis() {
  console.log(this);
}
checkThis();

What is the problem if you want to log the global object using this inside checkThis?

medium

A. this is undefined because of strict mode inside the function

B. this points to the global object as expected

C. this points to the function itself

D. Syntax error due to strict mode

Solution

1. Step 1: Understand strict mode effect inside functions

   In strict mode, this inside a regular function called without an object is undefined.

2. Step 2: Check the function call context

   The function checkThis is called directly, so this is not bound to the global object.

3. Final Answer:

   this is undefined because of strict mode inside the function -> Option A

4. Quick Check:

   Strict mode makes this undefined in functions called globally [OK]

Hint: Strict mode sets this to undefined inside functions [OK]

Common Mistakes:

• Assuming this always points to global object
• Thinking strict mode causes syntax errors here
• Confusing function this with global this

5. You want to create a global variable myGlobal and access it via this.myGlobal in the global scope under strict mode. Which code snippet correctly achieves this in a browser environment?

hard

A. window.myGlobal = 10; console.log(this.myGlobal);

B. let myGlobal = 10; console.log(this.myGlobal);

C. const myGlobal = 10; console.log(this.myGlobal);

D. var myGlobal = 10; console.log(this.myGlobal);

Solution

1. Step 1: Understand variable declaration and global object

   In strict mode, variables declared with var, let, or const do not become properties of window.

2. Step 2: Check how to explicitly add property to global object

   Assigning window.myGlobal = 10 explicitly adds myGlobal as a property of the global object.

3. Final Answer:

   window.myGlobal = 10; console.log(this.myGlobal); -> Option A

4. Quick Check:

   Only window.myGlobal ensures this.myGlobal exists globally [OK]

Hint: Use window.myGlobal to add global property reliably [OK]

Common Mistakes:

• Using let or const expecting global this property
• Assuming var always adds property to this in all contexts
• Not understanding difference between variable and global object property