Which is better to use undefined or null in js?

In general, it is better to use null than undefined. undefined means that the variable is not assigned a value, and null means that the value is clearly "none"; undefined is a primitive type, and null is an object type; null can be assigned to an object, but undefined cannot; in strict equality comparison, undefined and null are not equal, in loose Equality in equality comparison.

Which one is better, undefined or null in JavaScript?

Direct answer: In general, it is better to use null than undefined.

Detailed explanation:

In JavaScript, undefined and null are special values, indicating that the variable is not assigned a value or a value does not exist. However, there are some key differences between the two:

• Primitive types: undefined is a primitive type, while null is an object type. This means that null can be assigned to an object, but undefined cannot.
• Meaning: undefined means that the variable is not assigned a value, while null means that the value is clearly "None".
• Comparison: undefined and null are not equal in strict equality (===) comparison, but are not equal in loose equality (==) Equality in comparison.

Under what circumstances should undefined be used?

Using undefined is appropriate when:

• The variable has not yet been assigned a value (for example: let x; )
• Parameters are not passed to the function (for example: function f(x) { if (x === undefined) {...} })
• Array or Undefined properties in objects (for example: const arr = []; arr[2] === undefined)

When to use it null?

It is better to use null in the following cases:

• Explicitly indicates that the value does not exist (for example: const user = null; )
• Assigned to object type variables (for example: const obj = null;)
• is used to represent null values ​​in the database (for example: const result = { id: 1, name: null })

Best practice:

Generally, use null It is better to explicitly indicate that the value does not exist. This helps improve code readability and maintainability, especially when dealing with complex applications. Additionally, using null avoids potential problems associated with undefined, such as accidentally overwriting a declared variable.

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