Should You Use == or === in JavaScript? Understanding Equality Operators and Performance

When writing JavaScript, many developers notice tools like JSLint or ESLint recommending the use of triple equals (===) instead of double equals (==). This raises two common questions:

Is there a performance difference between == and ===?
Why do strict equality comparisons matter if both seem to return the same results in many cases?

Let’s break down the difference between these operators and see which one you should use in modern JavaScript development.

Should You Use or in JavaScript Understanding Equality Operators and Performance

coldshadow44 on 2025-10-15

Comment

Showing comments related to this post.

_coldshadow44

2025-10-15

The strict equality operator (===) and the abstract equality operator (==) both compare two values in JavaScript, but they behave very differently when it comes to type conversion.

1. Main Difference Between == and ===

== compares two values for equality after performing type coercion if necessary.
=== compares both the value and the type without performing any type conversion.

Example:

0 == '0' // true (type conversion happens)

0 === '0' // false (different types)

When you use ===, JavaScript checks equality more predictably because it doesn’t attempt to convert one type into another before comparison. This prevents subtle bugs caused by unexpected type coercions.

2. Is === Faster Than ==?

In modern JavaScript engines, there’s no meaningful performance difference between == and ===. Both execute extremely quickly.

However, === can be considered more efficient in logic, since the interpreter doesn’t have to perform type coercion checks internally. Still, the performance difference is so small that it’s not noticeable in real-world scenarios.

The main reason to use === isn’t performance — it’s reliability and predictability.

3. Why JSLint and ESLint Recommend ===

Linting tools like JSLint warn against == because of its confusing type coercion rules.

Here are some surprising results caused by ==:

'' == '0' // false

0 == '' // true

0 == '0' // true

false == '0' // true

null == undefined // true

' \t\r\n ' == 0 // true

These behaviors are difficult to remember and can lead to logic errors. Using === eliminates that risk entirely.

4. Comparing Objects with == and ===

For objects, both == and === work the same way — they check reference equality, not value equality.

Example:

const a = [1, 2, 3];

const b = [1, 2, 3];

a == b; // false

a === b; // false

Each array is a different object in memory, so both comparisons return false.

The only exception occurs when comparing a primitive to an object that represents the same primitive value:

"abc" == new String("abc"); // true (coercion happens)

"abc" === new String("abc"); // false (different types)

The strict comparison is more accurate because "abc" (a primitive) and new String("abc") (an object) are not the same type.

5. Best Practice

Always use === and !== instead of == and != unless you have a very specific reason to allow type coercion.

This ensures your code behaves consistently and avoids unexpected comparison results.

Summary:

=== checks type and value — safer and more predictable.
== performs type conversion — can lead to subtle bugs.
There is no measurable performance advantage to using one over the other.
Linting tools recommend === because it promotes clean, reliable code.

In short: use === and !== by default to write modern, bug-free JavaScript.

Ask. Code. Learn. Grow with the Developer Community.