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Write the main difference between '==' and '===' operators in javascript?
The main difference between == and === operators in JavaScript is that == performs type coercion (converts types before comparing), while === performs strict comparison without any type conversion.
The == Operator (Loose Equality)
The == operator compares values after converting them to the same type if needed. This can lead to unexpected results.
Example
<html>
<body>
<p id="loose"></p>
<script>
var x = 5;
var y = "5";
var z = 6;
document.getElementById("loose").innerHTML =
(x == y) + "<br>" + (x == z);
</script>
</body>
</html>
Output
true false
Notice that 5 == "5" returns true because JavaScript converts the string "5" to the number 5 before comparison.
The === Operator (Strict Equality)
The === operator compares both value and type without any conversion. Both operands must be of the same type and have the same value to return true.
Example
<html>
<body>
<p id="strict"></p>
<script>
var x = 5;
var y = "5";
var z = 5;
document.getElementById("strict").innerHTML =
(x === y) + "<br>" + (x === z);
</script>
</body>
</html>
Output
false true
Here, 5 === "5" returns false because the number 5 and string "5" have different types, while 5 === 5 returns true.
Key Differences
| Operator | Name | Type Conversion | Comparison |
|---|---|---|---|
== |
Loose Equality | Yes | Value only (after conversion) |
=== |
Strict Equality | No | Value and type |
Common Examples
<html>
<body>
<p id="examples"></p>
<script>
document.getElementById("examples").innerHTML =
"0 == false: " + (0 == false) + "<br>" +
"0 === false: " + (0 === false) + "<br>" +
"null == undefined: " + (null == undefined) + "<br>" +
"null === undefined: " + (null === undefined);
</script>
</body>
</html>
Output
0 == false: true 0 === false: false null == undefined: true null === undefined: false
Best Practice
It's recommended to use === (strict equality) in most cases to avoid unexpected type conversions and make your code more predictable.
Conclusion
Use === for reliable comparisons that check both value and type. Reserve == only when you specifically need type coercion behavior.
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