Operator precedence in Javascript

Introduction

Operator precedence tells JavaScript which part of a math or logic problem to solve first. It helps avoid confusion and mistakes.

When you write math calculations with multiple operators like +, -, *, /

When you combine logic checks like &&, ||, and ! in one statement

When you want to understand how JavaScript reads your code without extra parentheses

When debugging why a calculation or condition gives an unexpected result

Syntax

Javascript

/* Example of operator precedence in JavaScript */
let result = 3 + 4 * 2;
// Multiplication (*) happens before addition (+)
console.log(result);

Operators like * and / have higher precedence than + and -.

Use parentheses () to change the order if needed.

Examples

Multiplication happens first: 3 * 2 = 6, then 5 + 6 = 11.

Javascript

let a = 5 + 3 * 2;
console.log(a);

Parentheses change order: 5 + 3 = 8, then 8 * 2 = 16.

Javascript

let b = (5 + 3) * 2;
console.log(b);

AND (&&) has higher precedence than OR (||), so false && false = false, then true || false = true.

Javascript

let c = true || false && false;
console.log(c);

NOT (!) has highest precedence: !false = true, then true && true = true.

Javascript

let d = !false && true;
console.log(d);

Sample Program

This program shows how operator precedence affects the results of calculations and logic expressions.

Javascript

let x = 10 + 5 * 2;
let y = (10 + 5) * 2;
let z = !false || false && true;

console.log('x =', x);
console.log('y =', y);
console.log('z =', z);

Important Notes

Remember: multiplication and division happen before addition and subtraction.

Logical NOT (!) happens before AND (&&), which happens before OR (||).

Use parentheses to make your code clear and control the order explicitly.

Summary

Operator precedence decides which operations run first in expressions.

Multiplication and division have higher precedence than addition and subtraction.

Use parentheses to change or clarify the order of operations.

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