Predictable Code

Functional Programming (FP) teaches us to write code so it's easy to test and understand.

1. Pure Functions

They always return the same result for the same inputs.
They have no side effects (they don't change external variables, don't log to the console, don't make network requests).

Instead of mutating an old object, a function returns a new one with the changes applied.

Note

Using pure functions makes your code " transparent " . You can replace a function call with its computed result, and nothing will break.

Tip

Try to write the core of your logic using pure functions, and push all " dirty " actions (DOM, APIs) to the edges of your program.