In JavaScript, variables and data types can be either mutable or immutable. Mutable objects and variables can be changed or modified, while immutable objects and variables cannot be changed or modified after they have been created.
A mutable object is an object whose state can be modified after it has been created. This means that you can change the properties of a mutable object, and those changes will be reflected in the object. Examples of mutable objects in JavaScript include arrays and objects.
In contrast, an immutable object is an object whose state cannot be modified after it has been created. This means that any operation that appears to modify an immutable object actually creates a new object with the modified state. Examples of immutable objects in JavaScript include strings and numbers.
The difference between mutable and immutable objects and variables is an important concept to understand in JavaScript, because it can have implications for performance, memory usage, and programming paradigms. In general, immutable objects are preferred for their safety and ease of use, while mutable objects are preferred for their flexibility and performance.
The key differences between mutable and immutable objects in JavaScript is below:
| Mutable Objects | Immutable Objects | |
|---|---|---|
| Definition | An object whose state can be modified after it has been created. | An object whose state cannot be modified after it has been created. |
| Examples | Arrays, objects | Strings, numbers, booleans |
| Operations | Operations that modify the object (e.g. push(), pop(), splice(), etc.) |
Operations that create a new object with the modified state (e.g. replace(), concat(), slice(), etc.) |
| Performance | Mutable objects can be more efficient for large datasets or frequent modifications. | Immutable objects can be more efficient for small datasets or infrequent modifications. |
| Safety | Mutable objects can be more error-prone, since modifications can affect other parts of the code. | Immutable objects are safer, since modifications create a new object and do not affect the original. |
| Functional Programming | Mutable objects can make functional programming more difficult, since they introduce side effects. | Immutable objects are more compatible with functional programming, since they are side-effect-free. |
In conclusion, mutable objects and variables in JavaScript can be changed or modified after they have been created, while immutable objects and variables cannot be changed or modified after they have been created. Mutable objects in JavaScript include arrays and objects, while immutable objects include strings and numbers.