null and undefined in JavaScript
In the Reverse a String in JavaScript blog, we learned about the different ways of reversing a string. Reversing a string can be achieved through various methods, such as using loops or recursion. In this blog, we will go through the null and undefined.
What is a null?
null is a language keyword that evaluates to a special value that is usually used to indicate the absence of a value.
What is undefined?
In JavaScript, undefined is a special value that represents the absence of a specific value. It is commonly assigned to variables that have not been initialized or used when querying the value of an object property or array element that does not exist.
Difference between null and undefined
null | undefined |
---|---|
null Indicates a special value that is commonly used to represent the absence of a value and can be considered as a special object value. | undefined is the value assigned to variables that haven't been initialized or when querying non-existent object properties or array elements. |
null is used to indicate null values. | undefined is used to indicate undefined values. |
The typeof operator on null returns the string "object,"suggesting it as a special object value. | The typeof operator on undefined returns the string"undefined," indicating it as the sole member of a special type. |
In ECMAScript 3, null is a read/write variable, meaning it can be set to any value. | undefined is read-only, and its value cannot be changed. |
null is often used at the program level to indicate a normal or expected absence of value. | undefined represents a system-level, unexpected, or error-like absence of value. |
In JavaScript, null signifies a purposeful absence of value, commonly used in programming scenarios. On the other hand, undefined represents a deeper absence, often associated with uninitialized variables or non-existent properties. While both are considered equal by ==, understanding their distinct use cases is crucial for effective coding. Choosing between them depends on whether you want to explicitly set an absence (null) or encountered an unexpected absence (undefined).