# Removing duplication with higher-order functions

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We sometimes call the same function many times in a row, where some parameters are the exact same every time. We can hide that repetition in a higher-order function.

Those higher-order functions can also help us create many similar functions.

``````// We could write a function that gives us the correct pluralization of a
// word for a given amount like this:
const pluralize = (singular, plural, count) => {
return count === 1 ? singular : plural
}

// We would call it like this, but we would have to repeat a lot of values:
pluralize("dog", "dogs", 0) // ⇒ "dogs"
pluralize("dog", "dogs", 1) // ⇒ "dog"
pluralize("dog", "dogs", 2) // ⇒ "dogs"

// Let’s split the parameters into two groups, adding an arrow between them:
const pluralize = (singular, plural) => count => {
return count === 1 ? singular : plural
}

// Because we have two arrows now, we also need two sets of parentheses.
// This works exactly as before, but so far looks like _more_ work for us:
pluralize("dog", "dogs")(0) // ⇒ "dogs"
pluralize("dog", "dogs")(1) // ⇒ "dog"
pluralize("dog", "dogs")(2) // ⇒ "dogs"

// Because this is really two function calls, we can extract the first one and assign it to a variable:
const pluralizeDog = pluralize("dog", "dogs")

// With this, we don’t have to repeat "dog" and "dogs" every time:
pluralizeDog(0) // ⇒ "dogs"
pluralizeDog(1) // ⇒ "dog"
pluralizeDog(2) // ⇒ "dogs"

// We can use this to make all kinds of pluralization-functions:
const pluralizeTable = pluralize("table", "tables")
const pluralizeHouse = pluralize("house", "houses")
const pluralizeSheep = pluralize("sheep", "sheep")``````
``````// We could write a function that gives us the correct pluralization of a
// word for a given amount like this:
const pluralize = (singular, plural, count) => {
return count === 1 ? singular : plural
}

// We would call it like this, but we would have to repeat a lot of values:
pluralize("dog", "dogs", 0) // ⇒ "dogs"
pluralize("dog", "dogs", 1) // ⇒ "dog"
pluralize("dog", "dogs", 2) // ⇒ "dogs"

// Let’s split the parameters into two groups, adding an arrow between them:
const pluralize = (singular, plural) => count => {
return count === 1 ? singular : plural
}

// Because we have two arrows now, we also need two sets of parentheses.
// This works exactly as before, but so far looks like _more_ work for us:
pluralize("dog", "dogs")(0) // ⇒ "dogs"
pluralize("dog", "dogs")(1) // ⇒ "dog"
pluralize("dog", "dogs")(2) // ⇒ "dogs"

// Because this is really two function calls, we can extract the first one and assign it to a variable:
const pluralizeDog = pluralize("dog", "dogs")

// With this, we don’t have to repeat "dog" and "dogs" every time:
pluralizeDog(0) // ⇒ "dogs"
pluralizeDog(1) // ⇒ "dog"
pluralizeDog(2) // ⇒ "dogs"

// We can use this to make all kinds of pluralization-functions:
const pluralizeTable = pluralize("table", "tables")
const pluralizeHouse = pluralize("house", "houses")
const pluralizeSheep = pluralize("sheep", "sheep")``````