content: add WIP of JS iterarive vs functional array helpers

src/content/docs/javascript/iterative-vs-functional.md

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+---
+authors:
+  - "@veksen"
+created_at: "2019/07/27"
+---
+
+# Iterative vs Functional array helpers
+
+-- placeholder --
+
+## find
+
+```js
+const users = [
+  { name: "Joe", age: 25 },
+  { name: "John", age: 17 },
+  { name: "Jane", age: 16 },
+]
+```
+
+Iterative way:
+
+```js
+let foundUser = null
+users.forEach(user => {
+  if (user.name === "John") {
+    foundUser = user
+  }
+})
+```
+
+Functional way:
+
+```js
+const foundUser = users.find(user => user.name === "John")
+```
+
+## filter
+
+```js
+const users = [
+  { name: "Joe", age: 25 },
+  { name: "John", age: 17 },
+  { name: "Jane", age: 16 },
+]
+```
+
+Iterative way:
+
+```js
+const youngerUsers = []
+users.forEach(user => {
+  if (user.age < 18) {
+    youngerUsers.push(user)
+  }
+})
+```
+
+Functional way:
+
+```js
+const youngerUsers = users.filter(user => user.age < 18)
+```
+
+## map
+
+```js
+const users = [
+  { name: "Joe", age: 25 },
+  { name: "John", age: 17 },
+  { name: "Jane", age: 16 },
+]
+```
+
+Iterative way:
+
+```js
+const userNames = []
+users.forEach(user => {
+  userNames.push(user.name)
+})
+```
+
+Functional way:
+
+```js
+const userNames = users.map(user => user.name)
+```
+
+## reduce
+
+```js
+const users = [
+  { name: "Joe", age: 25 },
+  { name: "John", age: 17 },
+  { name: "Jane", age: 16 },
+]
+```
+
+Iterative way:
+
+```js
+let totalAge = 0
+users.forEach(user => {
+  totalAge += user.age
+})
+```
+
+Functional way:
+
+```js
+const totalAge = users.reduce((acc, user) => acc + user.age)
+```
+
+## some
+
+```js
+const users = [
+  { name: "Joe", age: 25 },
+  { name: "John", age: 17 },
+  { name: "Jane", age: 16 },
+]
+```
+
+Iterative way:
+
+```js
+let hasYoungUsers = false
+for (let i = 0; users.length > i; i++) {
+  if (user > 18) {
+    hasYoungUsers = true
+    break
+  }
+}
+```
+
+Functional way:
+
+```js
+const hasYoungUsers = users.some(user => user.age < 18)
+```
+
+## every
+
+```js
+const users = [
+  { name: "Joe", age: 25 },
+  { name: "John", age: 17 },
+  { name: "Jane", age: 16 },
+]
+```
+
+Iterative way:
+
+```js
+let allUsersAreOldEnough = true
+for (let i = 0; users.length > i; i++) {
+  if (user.age > 18) {
+    allUsersAreOldEnough = false
+    break
+  }
+}
+```
+
+Functional way:
+
+```js
+const hasYoungUsers = users.some(user => user.age < 18)
+```
+
+## inludes
+
+```js
+const pets = ["cat", "dog", "bat"]
+```
+
+Iterative way:
+
+```js
+let found = false
+pets.forEach(pet => {
+  if (pet === "dog") {
+    found = true
+  }
+})
+
+// or most of the time done with indexOf
+pets.indexOf("dogs") > 0
+```
+
+Functional way:
+
+```js
+pets.includes("dogs")
+```