Iteration: A Gentle Introduction to Functional Programming

The article uses simple JavaScript examples to show how functional programming turns repeated loop logic into small reusable functions. It starts with printing names from a list, then generalizes the idea with forEach and map, and then makes property access and transformations more explicit with prop, curry, and compose.

Reading notes

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• A loop that prints names can be wrapped in a function so the iteration details stay hidden and the caller only needs to know what the function does.
• The same iteration pattern can print ages instead of names by changing only the action applied to each item, not the loop structure.
• forEach expresses the idea of iterating over a list and performing a function on each item.
• map expresses the idea of building a new list by transforming each value, instead of changing the original list.
• prop is introduced to read a given property from an object, and then rewritten as a curried function so it can be partially applied.
• currying lets map receive a transformation function created earlier, which makes dependencies more explicit.
• compose is described as a helper that takes several functions and returns one function that applies them in reverse order to an initial value.
• Small functions such as prop, curry, and uppercase are presented as reusable pieces that can be combined to solve domain-specific tasks.
• The article links functional style to simpler unit testing because each function depends only on its input and output.
• It also argues that this style improves productivity by making code easier to reuse across problems.