Compare Operators

JavaScript provides several operators to compare values for equality and inequality. The most commonly used ones are:

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1. == (Equality Operator)

• Compares two values for equality after performing type conversion, if necessary.
• Known as the “loose equality” operator.

• Example:

  console.log(5 == '5');  // true (type conversion occurs)
  console.log(true == 1); // true (true is converted to 1)
  console.log(null == undefined); // true (special case)
  

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2. === (Strict Equality Operator)

• Compares two values for equality without performing type conversion.
• Both the value and the type must be the same.
• Known as the “strict equality” operator.

• Example:

  console.log(5 === '5');  // false (different types)
  console.log(true === 1); // false (different types)
  console.log(null === undefined); // false (different types)
  

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3. != (Inequality Operator)

• Compares two values for inequality after performing type conversion, if necessary.
• Opposite of ==.

• Example:

  console.log(5 != '5');  // false (type conversion occurs)
  console.log(true != 1); // false (type conversion occurs)
  

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4. !== (Strict Inequality Operator)

• Compares two values for inequality without performing type conversion.
• Opposite of ===.

• Example:

  console.log(5 !== '5');  // true (different types)
  console.log(true !== 1); // true (different types)
  

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Key Differences Between == and ===

Operator	Type Conversion?	Example	Result
==	Yes	5 == '5'	true
===	No	5 === '5'	false

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Special Cases to Remember

1. null and undefined:
   • null == undefined is true because they are loosely equal.
   • null === undefined is false because they are different types.
2. NaN (Not-a-Number):
   • NaN == NaN and NaN === NaN are both false.
   • Use Number.isNaN() to check for NaN.

   console.log(NaN == NaN);  // false
   console.log(Number.isNaN(NaN)); // true
   

3. 0 and false:
   • 0 == false is true (loose equality).
   • 0 === false is false (strict equality).
4. Empty String (""):
   • "" == false is true (loose equality).
   • "" === false is false (strict equality).

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When to Use

• === and !==: Use these by default for type-safe comparisons.
• == and !=: Use these when type coercion is explicitly desired (use sparingly).