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

Question

Explain the difference between loose equality (==) and strict equality (===) operators in JavaScript. When would you use one over the other?

JSExpert · Accepted Answer

The key difference is **type coercion**:

## Loose Equality (==)
Converts operands to the same type before comparing:

```javascript
5 == "5"      // true (string converted to number)
null == undefined  // true
0 == false    // true
"" == false   // true
```

## Strict Equality (===)
No type conversion - both value AND type must match:

```javascript
5 === "5"     // false (different types)
null === undefined  // false
0 === false   // false
"" === false  // false
```

## Best Practice
**Always use `===`** unless you have a specific reason to use `==`. It prevents subtle bugs from unexpected type coercion.

The only common exception: `value == null` checks for both `null` and `undefined` in one comparison.

LintFan · Answer

Quick tip: ESLint has the `eqeqeq` rule that enforces strict equality. Enable it in your projects:

```json
{
  "rules": {
    "eqeqeq": ["error", "always"]
  }
}
```

This catches accidental use of `==` during development.

2 Answers