Operator precedence in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is operator precedence in JavaScript?

Operator precedence determines the order in which operators are evaluated in an expression. Operators with higher precedence are evaluated before those with lower precedence.

beginner

Which operator has higher precedence: multiplication (*) or addition (+)?

Multiplication (*) has higher precedence than addition (+), so it is evaluated first in an expression.

beginner

How does parentheses affect operator precedence?

Parentheses have the highest precedence and force the expression inside them to be evaluated first, regardless of other operators.

beginner

What is the result of the expression: 3 + 4 * 2?

The multiplication happens first: 4 * 2 = 8. Then addition: 3 + 8 = 11. So, the result is 11.

beginner

True or False: The assignment operator (=) has higher precedence than addition (+).

False. The addition operator (+) has higher precedence than the assignment operator (=). So addition happens before assignment.

Which operator is evaluated first in the expression: 5 + 3 * 2?

A Multiplication (*)

B Addition (+)

C Left to right

D Assignment (=)

Multiplication (*) has higher precedence than addition (+), so it is evaluated first.

What does parentheses do in an expression?

A They lower operator precedence

B They force evaluation inside them first

C They change operator types

D They have no effect

Parentheses have the highest precedence and force the expression inside to be evaluated first.

Which operator has the lowest precedence?

A Multiplication (*)

B Addition (+)

C Assignment (=)

D Exponentiation (**)

Assignment (=) has lower precedence than arithmetic operators like +, *, and **.

What is the result of: (2 + 3) * 4?

A 5

B 14

C 24

D 20

Parentheses evaluated first: 2 + 3 = 5, then multiplied by 4 = 20.

In the expression 10 - 4 + 2, which operator is evaluated first?

A Subtraction (-)

B Addition (+)

C Both at the same time

D Depends on parentheses

Subtraction and addition have the same precedence and are evaluated left to right, so subtraction happens first.

Explain how operator precedence affects the evaluation of the expression 8 + 2 * 5.

Think about which operation happens first without parentheses.

Describe the role of parentheses in changing the order of operations in JavaScript expressions.

Consider how parentheses can change 2 + 3 * 4 to (2 + 3) * 4.

Practice

1. Which operator has the highest precedence in the expression 3 + 4 * 2?

easy

A. Multiplication (*)

B. Addition (+)

C. Subtraction (-)

D. Division (/)

Solution

1. Step 1: Recall operator precedence rules

   Multiplication and division have higher precedence than addition and subtraction.

2. Step 2: Identify operators in the expression

   The expression has addition (+) and multiplication (*). Multiplication runs first.

3. Final Answer:

   Multiplication (*) -> Option A

4. Quick Check:

   Multiplication > Addition [OK]

Hint: Multiplication/division run before addition/subtraction [OK]

Common Mistakes:

• Thinking addition runs before multiplication
• Ignoring operator precedence
• Assuming left-to-right always applies

2. Which of the following expressions is syntactically correct in JavaScript?

easy

A. 5 + (3 * 2)

B. 5 + * 3

C. 5 + 3 * )2(

D. 5 + 3 * 2)

Solution

1. Step 1: Check each expression for syntax errors

   5 + * 3 has two operators in a row (+ *), which is invalid. 5 + 3 * )2( has misplaced parentheses. 5 + 3 * 2) has an unmatched closing parenthesis.

2. Step 2: Confirm correct syntax

   5 + (3 * 2) uses parentheses correctly and has valid operators and operands.

3. Final Answer:

   5 + (3 * 2) -> Option A

4. Quick Check:

   Valid parentheses and operators [OK]

Hint: Check parentheses and operator placement carefully [OK]

Common Mistakes:

• Misplacing parentheses
• Using two operators together
• Unmatched parentheses

3. What is the output of the following code?

console.log(10 - 2 * 3 + 4 / 2);

medium

A. 8

B. 12

C. 6

D. 10

Solution

1. Step 1: Apply operator precedence

   Multiplication (*) and division (/) run before addition (+) and subtraction (-). Calculate 2 * 3 = 6 and 4 / 2 = 2 first.

2. Step 2: Calculate remaining expression

   Expression becomes 10 - 6 + 2. Calculate left to right: 10 - 6 = 4, then 4 + 2 = 6.

3. Final Answer:

   6 -> Option C

4. Quick Check:

   10 - 6 + 2 = 6 [OK]

Hint: Do * and / before + and -, then left to right [OK]

Common Mistakes:

• Adding before multiplying
• Ignoring division precedence
• Calculating right to left

4. Find the error in this expression:

let result = 5 + 3 * / 2;

medium

A. No error, expression is valid

B. Incorrect use of parentheses

C. Division operator should be replaced with subtraction

D. Missing operand between * and /

Solution

1. Step 1: Analyze the operator sequence

   The expression has '* /' operators together without a number between them, which is invalid syntax.

2. Step 2: Identify the syntax error

   Every operator needs operands on both sides. Here, the '*' operator is missing its right operand before the '/' operator.

3. Final Answer:

   Missing operand between * and / -> Option D

4. Quick Check:

   Operators need operands on both sides [OK]

Hint: Operators must have numbers on both sides [OK]

Common Mistakes:

• Ignoring missing operand
• Assuming expression is valid
• Confusing operator roles

5. Given the expression let x = 4 + 3 * 2 ** 2 / (1 + 1);, what is the value of x?

hard

A. 13

B. 10

C. 11

D. 14

Solution

1. Step 1: Evaluate parentheses and exponentiation first

   Parentheses: (1 + 1) = 2. Exponentiation: 2 ** 2 = 4.

2. Step 2: Calculate multiplication and division left to right

   Expression becomes 4 + 3 * 4 / 2. Calculate 3 * 4 = 12, then 12 / 2 = 6.

3. Step 3: Perform addition

   Finally, 4 + 6 = 10.

4. Final Answer:

   10 -> Option B

5. Quick Check:

   Parentheses & exponentiation first, then * /, then + [OK]

Hint: Do parentheses, then **, then * /, then + [OK]

Common Mistakes:

• Ignoring exponentiation precedence
• Doing addition before multiplication
• Miscomputing parentheses