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Article by TK on Medium.com
Programs developed using collections of functions to do work rather than lists of statements (like in a script).
What is a pure function and how do we know if something is a pure function?
Is deterministic: The function will return the same result given the same input, and does not cause any observable side effects.
It does not rely on global objects (variables, files, etc) that are not passed-in explicitly as parameters.
Does not utilize an internal random generator.
Will not modify any global object or parameter passed by reference.
What are the benefits of a pure function?
All inputs are known and the output is predictable.
As stated in the article: "Given param A => expect the function to return value B"
What is immutability?
Changing the value stored in memory mutates the memory (variable). Immutability is a property of dissallowing change in that memory location. Strings are immutable, so every time they have a value reassigned, they are actually changing the memory state.
What is Referential transparency?
Given the same inputs, functions that are referentially transparent always return the same result. As the author put it: "pure functions + immutable data = referential transparency" [TK on Medium.com, accessed 21-Apr-22]
What is a module?
A small piece of executable code that is easy to maintain, and has a specific purpose.
What does the word 'require' do?
When we want to use a module in node.js.
How do we bring another module into the file that we are working in?
Use
require(./path-to-file);
What do we have to do to make a module available?
Use
module.exports = what-functions-to-be-made-available
At that point, use a require statement in the calling module and assign the require output to a local variable.
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