Switch statement in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a switch statement used for in JavaScript?

A switch statement is used to perform different actions based on different conditions. It checks a value against multiple cases and runs the matching block of code.

beginner

How do you write a basic switch statement syntax?

Use switch(expression) { case value1: // code break; case value2: // code break; default: // code } to compare the expression with values and run matching code.

intermediate

What happens if you forget to add break in a switch case?

Without break, the code will continue running the next cases even if they don't match. This is called "fall-through" behavior.

beginner

What is the purpose of the default case in a switch statement?

The default case runs if none of the other cases match the expression. It acts like a fallback or else condition.

intermediate

Can a switch statement compare different data types?

Yes, but the comparison uses strict equality (===), so the type and value must match exactly for a case to run.

What keyword stops the execution of more cases in a switch statement?

A stop

B break

C exit

D return

The break keyword stops the switch from running the next cases.

What happens if no case matches and there is no default case?

A Nothing happens, switch ends

B The switch runs the first case

C An error is thrown

D The program crashes

If no case matches and no default is provided, the switch does nothing and continues.

Which comparison does switch use between expression and case values?

A Strict equality (===)

B Less than (<)

C Greater than (>)

D Loose equality (==)

Switch uses strict equality (===), so type and value must match.

Can multiple cases share the same code block in a switch?

A Only if they have the same value

B No, each case must have unique code

C Yes, by stacking cases without break

D Only inside the default case

You can stack cases without break to share the same code block.

What is the role of the default case?

A To stop the switch statement

B To declare variables

C To repeat the first case

D To run code if no other case matches

The default case runs when no other case matches the expression.

Explain how a switch statement works and why you need the break keyword.

Think about how you choose actions based on different options.

Describe what happens if you omit the default case in a switch statement.

Consider what happens when none of the options fit.

Practice

1. What is the main purpose of a switch statement in JavaScript?

easy

A. To choose which block of code to run based on a value

B. To repeat a block of code multiple times

C. To define a function

D. To create a new variable

Solution

1. Step 1: Understand the role of switch

   A switch statement checks a value and runs code matching that value.

2. Step 2: Compare with other options

   Repeating code is for loops, defining functions is with function keyword, and variables use let/const/var.

3. Final Answer:

   To choose which block of code to run based on a value -> Option A

4. Quick Check:

   Switch = choose code by value [OK]

Hint: Switch picks code based on one value quickly [OK]

Common Mistakes:

• Confusing switch with loops
• Thinking switch defines functions
• Believing switch creates variables

2. Which of the following is the correct syntax to start a switch statement in JavaScript?

easy

A. switch value { }

B. switch { value }

C. switch (value) { }

D. switch: (value) { }

Solution

1. Step 1: Recall switch syntax

   The switch statement requires parentheses around the value and curly braces for cases: switch (value) { ... }

2. Step 2: Check each option

   switch (value) { } matches correct syntax; others miss parentheses or use wrong symbols.

3. Final Answer:

   switch (value) { } -> Option C

4. Quick Check:

   Correct switch syntax uses parentheses and braces [OK]

Hint: Switch needs (value) and {cases} to work [OK]

Common Mistakes:

• Omitting parentheses around value
• Using curly braces instead of parentheses
• Adding colon after switch keyword

3. What will be the output of this code?

const day = 3;
switch(day) {
  case 1:
    console.log('Monday');
    break;
  case 2:
    console.log('Tuesday');
    break;
  case 3:
    console.log('Wednesday');
    break;
  default:
    console.log('Unknown day');
}

medium

A. Monday

B. Tuesday

C. Unknown day

D. Wednesday

Solution

1. Step 1: Match the value with cases

   The variable day is 3, so the switch looks for case 3.

2. Step 2: Identify executed case

   Case 3 matches and prints 'Wednesday', then break stops further checks.

3. Final Answer:

   Wednesday -> Option D

4. Quick Check:

   day=3 matches case 3 = Wednesday [OK]

Hint: Match value to case, break stops after match [OK]

Common Mistakes:

• Forgetting break causes fall-through
• Choosing default when case matches
• Mixing up case numbers and outputs

4. Find the error in this switch statement:

const color = 'red';
switch(color) {
  case 'red'
    console.log('Stop');
    break;
  case 'green':
    console.log('Go');
    break;
  default:
    console.log('Wait');
}

medium

A. Wrong variable name in switch

B. Missing colon ':' after case 'red'

C. Missing break after case 'red'

D. Missing default case

Solution

1. Step 1: Check case syntax

   Each case must end with a colon ':' after the value. Here, case 'red' misses the colon.

2. Step 2: Verify other parts

   Break is present after case 'red' block, variable name is correct, and default exists.

3. Final Answer:

   Missing colon ':' after case 'red' -> Option B

4. Quick Check:

   Case needs ':' after value [OK]

Hint: Each case must end with ':' before code [OK]

Common Mistakes:

• Omitting colon after case value
• Forgetting break causing fall-through
• Missing default case (not always error)

5. You want to print 'Weekend' for days 6 and 7, and 'Weekday' for days 1 to 5 using a switch. Which code correctly does this?

hard

A. switch(day) {
case 6:
case 7:
console.log('Weekend');
break;
case 1:
case 2:
case 3:
case 4:
case 5:
console.log('Weekday');
break;
default:
console.log('Invalid day');
}

B. switch(day) {
case 6:
console.log('Weekend');
case 7:
console.log('Weekend');
break;
case 1:
case 2:
case 3:
case 4:
case 5:
console.log('Weekday');
break;
default:
console.log('Invalid day');
}

C. switch(day) {
case 6:
case 7:
console.log('Weekend');
case 1:
case 2:
case 3:
case 4:
case 5:
console.log('Weekday');
break;
default:
console.log('Invalid day');
}

D. switch(day) {
case 6:
case 7:
console.log('Weekend');
break;
case 1:
case 2:
case 3:
case 4:
case 5:
console.log('Weekday');
default:
console.log('Invalid day');
}

Solution

1. Step 1: Group cases for weekend and weekday

   Cases 6 and 7 should print 'Weekend' with one console.log and break after.

2. Step 2: Group cases 1 to 5 for 'Weekday' with break

   Cases 1-5 print 'Weekday' and break to avoid fall-through.

3. Step 3: Check default for invalid days

   Default prints 'Invalid day' if no case matches.

4. Final Answer:

   switch(day) { case 6: case 7: console.log('Weekend'); break; case 1: case 2: case 3: case 4: case 5: console.log('Weekday'); break; default: console.log('Invalid day'); } -> Option A

5. Quick Check:

   Group cases, use break to stop fall-through [OK]

Hint: Group cases without code, break after last case [OK]

Common Mistakes:

• Missing break causing fall-through
• Repeating console.log in each case unnecessarily
• Omitting default case for invalid input