First commit

Author: alejandrosobko

README.md

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+## Recursive javascript
+
+Common functions implemented using recursion
+
+---
+
+### Implemented:
+
+- map
+- filter
+- flatten
+
+### Suggestions?
+
+Please create an issue!

filter.js

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+/**
+ *
+ * @param {Array} arr array of elements
+ * @param {Function} fn function that checks if the element satisfy the condition
+ * @returns {Array} a new array with the elements that satisfy the condition
+ */
+ function filter(arr, condition) {
+  if (arr.length === 0) return []
+  const x = arr[0]
+  const xs = arr.slice(1)
+  return (condition(x) ? [x] : []).concat(filter(xs, condition))
+}
+
+
+const greaterThanTwo = (e) => e > 2
+
+console.log(filter([1,2,3], greaterThanTwo))
+console.log(filter([2], greaterThanTwo))
+console.log(filter([], greaterThanTwo))
+console.log(filter([-1, 2, 44], greaterThanTwo))
+
+const isTrue = (e) => e
+console.log(filter([true, true, false], isTrue))

flatten.js

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+/**
+ *
+ * @param {Array} arr array multi level
+ * @returns {Array} a new array with the elements in the same level
+ */
+function flatten(arr) {
+  if (arr.length === 0) return []
+  const x = arr[0]
+  const xs = arr.slice(1)
+  if (arr.length === 1) return Array.isArray(x) ? flatten(x) : [x]
+  return flatten([x]).concat(flatten(xs))
+}
+
+console.log(flatten([]))
+console.log(flatten([1]))
+console.log(flatten([1,2]))
+console.log(flatten([1,2,3]))
+console.log(flatten([1,2, [3, 4, [[[5], 6], 7]]]))

map.js

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+/**
+ *
+ * @param {Array} arr array of elements
+ * @param {Function} fn function to be applied to each element
+ * @returns {Array} a new array with the function applied to each elements
+ */
+function map(arr, fn) {
+  if (arr.length === 0) return []
+  const x = arr[0]
+  const xs = arr.slice(1)
+  return [fn(x)].concat(map(xs, fn))
+}
+
+
+const plusOne = (e) => e + 1
+console.log(map([1,2,3], plusOne))
+console.log(map([2], plusOne))
+console.log(map([], plusOne))
+
+const getName = (e) => e.name
+const objs = [
+  {name: 'Ale', age: 27},
+  {name: 'Juan', age: 27},
+  {name: 'Maria', age: 27},
+]
+console.log(map(objs, getName))