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Cover image for Front-End Analogies: Closure's Coffee — Partial Application

Front-End Analogies: Closure's Coffee — Partial Application

Kevin K. Johnson
A Front-End Developer with a passion for learning how people work, the efficacy of good design, and a growing interest in the complexities of functional programming.
・2 min read

Ordering Coffee

Partial Application

Joe has a coffee addiction. It's not in the DSM-5, so who cares? Time to make a profit.

What do we know about this bozo? His name's Joe. He always gets two cups. One is going to be coffee with milk, but we'll say it in French—café au lait—to charge more. The second one, he likes to mix that up. Could be anything.


"use strict";

customerName = (_personName) => {
    return `${_personName} wants `;
}

buyTwoDrinks = (_firstCoffeeName) => {
    const secondDrink = (_secondCoffeeName) => {
        return `${_firstCoffeeName} and ${_secondCoffeeName}.`;
    }

    return secondDrink;
}

let Joe = customerName('Joe');
// What kinda clown's name is this?
// Prolly doesn't know his order yet cuz he spent too much time honkin' his nose.

let JoesUsual = buyTwoDrinks('Cafe au Lait');
// Usual baristas [functions] are like,
// "I want both these drink orders [parameters] right damn now."
// This bro is chill about it. We've got the first one on-deck,
// but we know we have to wait a little bit.

// When Joe comes in over the course of the week to order,
// it might look a little like this:

console.log( Joe + JoesUsual('Espresso') );
// Joe wants Cafe au Lait and Espresso.

console.log( Joe + JoesUsual('Nitro Cold Brew') );
// Joe wants Cafe au Lait and Nitro Cold Brew.

// This is a lot easier and less error-prone than writing:

console.log( customerName('Joe') + buyTwoDrinks('Cafe au lait')('Chai latte') );
// Joe wants Cafe au Lait and Chai latte.

console.log( customerName('Joe') + buyTwoDrinks('Cafe au lait')('Flat white') );
// Joe wants Cafe au Lait and Flat white.

// Gotta save time. You ever seen Joe without his caffeine for too long?
// It's less clown college and more Dark Knight Returns.

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