Nested conditional statements in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a nested conditional statement in JavaScript?

A nested conditional statement is an if or else statement placed inside another if or else block. It helps check multiple conditions step-by-step.

beginner

Why use nested conditional statements?

Nested conditionals let you make decisions that depend on more than one condition. For example, checking if a person is a teenager and if they have a driver's license.

beginner

How does JavaScript decide which block to run in nested conditionals?

JavaScript checks the outer condition first. If it is true, it then checks the inner condition(s). It runs the code inside the first true condition it finds.

beginner

Example: What will this code print?<br><pre>let age = 20;
if (age &gt;= 18) {
  if (age &lt;= 25) {
    console.log('Young adult');
  } else {
    console.log('Adult');
  }
} else {
  console.log('Minor');
}</pre>

It will print Young adult because age is 20, which is between 18 and 25, so the inner if condition is true.

intermediate

Can nested conditionals be replaced by other structures?

Yes, sometimes nested conditionals can be replaced by else if chains or switch statements for clearer code, but nesting is useful for checking conditions inside other conditions.

What does a nested conditional statement allow you to do?

A Check multiple conditions inside each other

B Run code without any conditions

C Only check one condition at a time

D Skip all conditions

Nested conditionals let you check one condition inside another, allowing multiple levels of decision-making.

In nested conditionals, which condition is checked first?

A The outer condition

B Both at the same time

C The inner condition

D None

The outer condition is checked first. Only if it is true does JavaScript check the inner condition.

What will this code print?

let x = 10;
if (x > 5) {
  if (x < 8) {
    console.log('A');
  } else {
    console.log('B');
  }
} else {
  console.log('C');
}

A Nothing

B A

C C

D B

x is 10, which is greater than 5 (outer condition true), but not less than 8 (inner condition false), so it prints 'B'.

Which keyword can sometimes replace nested conditionals for clarity?

A while

B Both C and D

C switch

D else if

Both else if chains and switch statements can sometimes replace nested conditionals for clearer code.

Is this a valid nested conditional?

if (a) {
  if (b) {
    // code
  }
}

A No

B Only if a and b are numbers

C Yes

D Only if a and b are strings

Yes, this is a valid nested conditional where one if statement is inside another.

Explain how nested conditional statements work in JavaScript and give a simple example.

Think about checking one condition inside another.

Describe a real-life situation where nested conditional statements would be useful.

Consider decisions that depend on more than one factor.

Practice

1. What does a nested conditional statement mean in JavaScript?
if (condition1) { if (condition2) { /* code */ } }

easy

A. A loop inside a condition

B. A condition inside another condition

C. Two conditions checked at the same time

D. A function inside a condition

Solution

1. Step 1: Understand the structure of nested conditionals

   Nested conditionals mean one if statement is placed inside another if statement's block.

2. Step 2: Identify the meaning of the code snippet

   The code checks condition1 first, and only if true, it checks condition2 inside it.

3. Final Answer:

   A condition inside another condition -> Option B

4. Quick Check:

   Nested conditional = condition inside condition [OK]

Hint: Look for if inside another if block [OK]

Common Mistakes:

• Thinking nested means conditions checked together
• Confusing nested conditionals with loops
• Assuming functions are involved

2. Which of the following is the correct syntax for nested if statements in JavaScript?

easy

A. if (a > 0) { if (b > 0) { console.log('Both positive'); } }

B. if (a > 0) if (b > 0) console.log('Both positive'); }

C. if (a > 0) { if (b > 0) console.log('Both positive'); } else }

D. if a > 0 { if b > 0 { console.log('Both positive'); } }

Solution

1. Step 1: Check proper use of braces and parentheses

   if (a > 0) { if (b > 0) { console.log('Both positive'); } } uses parentheses for conditions and braces to group code blocks correctly.

2. Step 2: Verify syntax correctness

   The other options have missing or misplaced braces or parentheses causing syntax errors.

3. Final Answer:

   if (a > 0) { if (b > 0) { console.log('Both positive'); } } -> Option A

4. Quick Check:

   Correct nested if syntax = if (a > 0) { if (b > 0) { console.log('Both positive'); } } [OK]

Hint: Match each if with parentheses and braces [OK]

Common Mistakes:

• Missing braces for inner if block
• Omitting parentheses around conditions
• Extra or misplaced braces

3. What will be the output of this code?

let x = 5;
if (x > 0) {
  if (x < 10) {
    console.log('A');
  } else {
    console.log('B');
  }
} else {
  console.log('C');
}

medium

A. No output

B. B

C. C

D. A

Solution

1. Step 1: Evaluate the outer if condition

   x = 5, which is greater than 0, so the outer if block runs.

2. Step 2: Evaluate the inner if condition

   Inside, x < 10 is true (5 < 10), so it prints 'A'.

3. Final Answer:

   A -> Option D

4. Quick Check:

   5 > 0 and 5 < 10 prints 'A' [OK]

Hint: Check outer condition first, then inner [OK]

Common Mistakes:

• Ignoring inner else block
• Confusing output with 'B' or 'C'
• Assuming no output if conditions are true

4. Find the error in this nested conditional code:

let num = 10;
if (num > 5) {
  if num < 15 {
    console.log('Inside range');
  }
}

medium

A. Using console.log incorrectly

B. Missing braces for outer if block

C. Missing parentheses around inner if condition

D. No error, code is correct

Solution

1. Step 1: Check syntax of inner if statement

   Inner if is written as if num < 15 { missing parentheses around condition.

2. Step 2: Confirm correct syntax for if statements

   JavaScript requires parentheses around conditions: if (num < 15) {.

3. Final Answer:

   Missing parentheses around inner if condition -> Option C

4. Quick Check:

   if conditions need parentheses [OK]

Hint: Always put parentheses around if conditions [OK]

Common Mistakes:

• Forgetting parentheses in if conditions
• Assuming braces are optional
• Thinking console.log causes error

5. You want to write a nested conditional that prints:
- 'Small positive' if a number is > 0 and < 10
- 'Large positive' if a number is >= 10
- 'Non-positive' otherwise
Which code correctly implements this?

hard

A. if (num > 0) { if (num < 10) { console.log('Small positive'); } else { console.log('Large positive'); } } else { console.log('Non-positive'); }

B. if (num > 0 && num < 10) { console.log('Small positive'); } else if (num >= 10) { console.log('Large positive'); } else { console.log('Non-positive'); }

C. if (num > 0) { if (num <= 10) { console.log('Small positive'); } else { console.log('Large positive'); } } else { console.log('Non-positive'); }

D. if (num >= 0) { if (num < 10) { console.log('Small positive'); } else { console.log('Large positive'); } } else { console.log('Non-positive'); }

Solution

1. Step 1: Check conditions for small positive numbers

   if (num > 0) { if (num < 10) { console.log('Small positive'); } else { console.log('Large positive'); } } else { console.log('Non-positive'); } checks if num > 0, then inside if num < 10 to print 'Small positive'.

2. Step 2: Check conditions for large positive and non-positive

   Else inside outer if prints 'Large positive' for num >= 10, else prints 'Non-positive'.

3. Step 3: Verify other options

   The option with combined conditions (&& and else if) is logically correct but does not use nested if statements. The option with outer condition num >= 0 incorrectly classifies 0 as 'Small positive'. The option with inner condition num <= 10 incorrectly classifies 10 as 'Small positive'.

4. Final Answer:

   if (num > 0) { if (num < 10) { console.log('Small positive'); } else { console.log('Large positive'); } } else { console.log('Non-positive'); } -> Option A

5. Quick Check:

   Nested if with correct ranges = if (num > 0) { if (num < 10) { console.log('Small positive'); } else { console.log('Large positive'); } } else { console.log('Non-positive'); } [OK]

Hint: Check each condition range carefully in nested ifs [OK]

Common Mistakes:

• Using <= instead of < for small positive
• Including zero as positive
• Not nesting conditions properly