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Home Web Front-end Front-end Q&A What is the difference between == and === in JavaScript

What is the difference between == and === in JavaScript

Jul 13, 2025 am 02:19 AM
comparison operator

In JavaScript, the main difference between == and === is type coercion. 1. == compares values after converting types if necessary, which can lead to unexpected results. 2. === compares both value and type without conversion, making it more predictable. For example, 5 == '5' is true but 5 === '5' is false. Use === for clarity and safety, and == only when intentional type coercion is needed.

In JavaScript, the main difference between == and === lies in how they compare values. The == operator checks for equality after performing type coercion if needed, while === checks for both value and type equality without any type conversion.

Type Coercion with ==

The == operator tries to make the operands the same type before comparing them. This means that if the types are different, JavaScript will attempt to convert one or both of the operands into a common type.

  • For example:
    • 5 == '5' returns true, because JavaScript converts the string '5' into a number before comparing.
    • 0 == false also returns true, since both are considered falsy values and are coerced into each other's type.

This behavior can sometimes lead to confusing or unexpected results, especially when dealing with different data types like strings, numbers, booleans, or null and undefined.

Strict Comparison with ===

The === operator, on the other hand, does not perform type coercion. It compares both the value and the type of the operands directly.

  • Using the earlier examples:
    • 5 === '5' returns false, because although the values look the same, their types (number vs string) are different.
    • 0 === false also returns false for the same reason—different types.

This makes === more predictable and safer to use in most cases, especially when you want to ensure that both the value and its type match exactly.

When to Use Which

If you're writing code where type matters—and it usually does—you should go with ===. It avoids surprises from automatic type conversion and makes your logic clearer.

However, there are rare situations where you might intentionally want coercion, such as when you expect mixed types but still want to treat them as equal (e.g., checking if a value is either 0 or the boolean false). In those cases, == might be appropriate—but use it carefully.

Basically, stick with === unless you have a specific reason to use ==.

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