JavaScript, null with comparison operator

In JavaScript, when one of the operands is null in a comparison, the behavior depends on the comparison operator being used. Here's a breakdown of how different operators behave:

1. Loose Equality (==)

The loose equality operator performs type coercion. When one of the operands is null, the comparison will be true only if both operands are null or both are undefined. The null and undefined are falsy values in JavaScript.

null == null        // true
null == undefined   // true
null == 0           // false
null == false       // false
null == ""          // false

2. Strict Equality (===)

The strict equality operator does not perform type coercion. For strict equality, the comparison will be true only if both operands are exactly the same value and type.

null === null       // true
null === undefined  // false
null === 0          // false
null === false      // false
null === ""         // false

3. Greater Than (>) / Less Than (<)

When using comparison operators like >, <, >=, or <=, null is treated as 0 when compared with a number. Therefore:

null > 0             // false
null < 0             // false
null >= 0            // true
null <= 0            // true

4. Loose Inequality (!=)

The loose inequality operator works similarly to loose equality (==), except it returns true when the operands are not equal. If one operand is null, the comparison will be true if the operands are not both null or both undefined.

null != null         // false
null != undefined    // false
null != 0            // true
null != false        // true

5. Strict Inequality (!==)

The strict inequality operator behaves like strict equality (===) but returns true if the operands are not strictly equal. So, when one operand is null, the comparison will return true if the operands are of different types or values.

null !== null        // false
null !== undefined   // true
null !== 0           // true
null !== false       // true

Summary

• ==: null == null and null == undefined are true, but other comparisons are false.
• ===: null === null is true, but comparisons with other types (like undefined, 0, etc.) return false.
• Comparison (>, <, >=, <=): null is treated as 0 in numerical comparisons.
• != and !==: Behave similarly to == and ===, but return true if the values are not equal or strictly different.