isImmutable

isImmutable is a JavaScript function commonly found in utility libraries like Lodash. Its primary purpose is to determine whether a given value is immutable. Immutability refers to the property of an object or value whose state cannot be modified after it is created.

When isImmutable is applied to a primitive value such as a number, string, boolean, null, or undefined, it will typically return true because primitive types in JavaScript are inherently immutable. Once declared, their value cannot be changed directly; operations that appear to modify them actually create new values.

For complex data structures like arrays and plain objects, isImmutable checks if these structures are "deeply immutable." This means not only the top-level structure but also all nested objects and arrays within it are also immutable. Libraries that provide isImmutable often have their own immutable collection types (e.g., Immutable.js) or mechanisms to create them. If the value is a standard JavaScript array or object that can be mutated, isImmutable will return false.

The function is useful in scenarios where maintaining data integrity is crucial, such as in state management for applications (e.g., Redux, Vuex) or in functional programming paradigms. By ensuring that data structures are immutable, developers can prevent unintended side effects, simplify change detection, and improve performance through techniques like memoization.