If statement in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of an if statement in JavaScript?

An if statement lets the program decide to run some code only if a condition is true. It helps the program make choices.

beginner

Write the basic syntax of an if statement in JavaScript.

The basic syntax is:

if (condition) {
  // code to run if condition is true
}

beginner

What happens if the condition in an if statement is false?

If the condition is false, the code inside the if block does not run. The program skips it and continues.

beginner

How do you add an alternative action if the if condition is false?

You use an else block after the if block. It runs when the if condition is false.

if (condition) {
  // runs if true
} else {
  // runs if false
}

intermediate

Can you check multiple conditions with if statements? How?

Yes, by using else if blocks between if and else. It checks conditions one by one until one is true.

if (cond1) {
  // code
} else if (cond2) {
  // code
} else {
  // code
}

What does this code do?

if (5 > 3) { console.log('Yes'); }

A Prints 'Yes' because 5 is greater than 3

B Prints nothing because 5 is not greater than 3

C Gives an error

D Prints 'No'

5 is greater than 3, so the condition is true and 'Yes' is printed.

Which keyword runs code when the if condition is false?

A else

B elseif

C then

D when

The else block runs when the if condition is false.

What will this code print?

if (false) { console.log('A'); } else { console.log('B'); }

A A

B Nothing

C B

D Error

The condition is false, so the else block runs and prints 'B'.

How do you check more than two conditions in an if statement?

A Use multiple <code>else</code> blocks

B Use multiple <code>else if</code> blocks

C Use <code>switch</code> only

D Use multiple <code>if</code> without else

You use else if blocks to check multiple conditions one after another.

What is the output of:

if (10 === '10') { console.log('Match'); } else { console.log('No match'); }

A Match

B Undefined

C Error

D No match

The triple equals === checks type and value. Number 10 is not the same type as string '10', so condition is false.

Explain how an if statement works in JavaScript and give a simple example.

Think about how you decide to do something only if a condition is true.

Describe how to use else if and else to handle multiple choices in JavaScript.

Imagine choosing between many options, checking one by one.

Practice

1. What does an if statement do in JavaScript?

easy

A. Declares a variable

B. Repeats code multiple times

C. Defines a new function

D. Runs code only if a condition is true

Solution

1. Step 1: Understand the purpose of an if statement

   An if statement checks a condition and runs code only when that condition is true.

2. Step 2: Compare options with the definition

   Only Runs code only if a condition is true matches this behavior exactly.

3. Final Answer:

   Runs code only if a condition is true -> Option D

4. Quick Check:

   If statement = runs code if true [OK]

Hint: If it runs code only when true, it's an if statement [OK]

Common Mistakes:

• Confusing if with loops
• Thinking if declares variables
• Mixing if with function definitions

2. Which of the following is the correct syntax for an if statement in JavaScript?

easy

A. if condition { console.log('Yes'); }

B. if (condition) console.log('Yes');

C. if condition: console.log('Yes');

D. if (condition) then { console.log('Yes'); }

Solution

1. Step 1: Recall JavaScript if syntax

   The condition must be inside parentheses, and the code block can be inside curly braces or a single statement without braces.

2. Step 2: Check each option

   if (condition) console.log('Yes'); correctly uses parentheses around the condition and a statement without braces.

3. Final Answer:

   if (condition) console.log('Yes'); -> Option B

4. Quick Check:

   Parentheses around condition = correct syntax [OK]

Hint: Condition must be in parentheses for if [OK]

Common Mistakes:

• Omitting parentheses around condition
• Using colons instead of braces
• Adding 'then' keyword (not in JS)

3. What will be the output of this code?

let x = 10;
if (x > 5) {
  console.log('Big');
} else {
  console.log('Small');
}

medium

A. Small

B. 10

C. Big

D. No output

Solution

1. Step 1: Evaluate the condition x > 5

   Since x is 10, which is greater than 5, the condition is true.

2. Step 2: Determine which block runs

   The if block runs and prints 'Big'. The else block is skipped.

3. Final Answer:

   Big -> Option C

4. Quick Check:

   10 > 5 is true, so output is 'Big' [OK]

Hint: Check if condition is true to pick output [OK]

Common Mistakes:

• Choosing else output when condition is true
• Confusing variable value with output
• Ignoring else block

4. Find the error in this code:

if x == 5 {
  console.log('Equal');
}

medium

A. Missing parentheses around condition

B. Using double equals instead of triple equals

C. Missing semicolon after console.log

D. Curly braces should be parentheses

Solution

1. Step 1: Check if statement syntax

   In JavaScript, the condition must be inside parentheses after if.

2. Step 2: Identify the error

   The code misses parentheses around x == 5, causing a syntax error.

3. Final Answer:

   Missing parentheses around condition -> Option A

4. Quick Check:

   Condition needs parentheses in if [OK]

Hint: Always put condition inside parentheses in if [OK]

Common Mistakes:

• Omitting parentheses around condition
• Confusing == and === (both valid but different)
• Thinking semicolon is mandatory after console.log

5. You want to print 'Adult' if age is 18 or more, otherwise 'Minor'. Which code correctly uses an if statement?

hard

A. if (age >= 18) { console.log('Adult'); } else { console.log('Minor'); }

B. if age >= 18 then { console.log('Adult'); } else { console.log('Minor'); }

C. if (age > 18) { console.log('Adult'); } else { console.log('Minor'); }

D. if (age = 18) { console.log('Adult'); } else { console.log('Minor'); }

Solution

1. Step 1: Check condition for age 18 or more

   The condition should be age >= 18 to include 18 and above.

2. Step 2: Verify syntax and logic

   if (age >= 18) { console.log('Adult'); } else { console.log('Minor'); } uses correct syntax and condition. if age >= 18 then { console.log('Adult'); } else { console.log('Minor'); } uses invalid 'then'. if (age > 18) { console.log('Adult'); } else { console.log('Minor'); } excludes age 18. if (age = 18) { console.log('Adult'); } else { console.log('Minor'); } uses assignment (=) instead of comparison (== or >=).

3. Final Answer:

   if (age >= 18) { console.log('Adult'); } else { console.log('Minor'); } -> Option A

4. Quick Check:

   Use >= and correct syntax for if-else [OK]

Hint: Use >= for 18 or more, no 'then' keyword [OK]

Common Mistakes:

• Using assignment (=) instead of comparison
• Using 'then' keyword (not in JS)
• Using > instead of >= to include 18