How to write X in both Python 3 and JavaScript (ES2015)

Math: Absolute Value

Python 3 / `abs`

# 100\nprint(abs(-100))\n# 50\nprint(abs(50))

JavaScript (ES2015) / `abs`

// 100\nconsole.log(Math.abs(-100))\n// 50\nconsole.log(Math.abs(50))

Math: Round Numbers

Python 3 / `ceil`, `floor`, `round`

import math\n\n# 2\nprint(math.ceil(1.5))\n# 1\nprint(math.floor(1.5))\n# 2\nprint(round(1.5))\n

JavaScript (ES2015) / `ceil`, `floor`, `round`

// 2\nconsole.log(Math.ceil(1.5))\n// 1\nconsole.log(Math.floor(1.5))\n// 2\nconsole.log(Math.round(1.5))\n

Math: Max and Min

Python 3 / `max`, `min`

# 100\nprint(max(100, 50))\n# 40\nprint(min(80, 40))\n

JavaScript (ES2015) / `max`, `min`

// 100\nconsole.log(Math.max(100, 50))\n\n// 40\nconsole.log(Math.min(80, 40))\n

Control Flow: If else

Python 3 / `if`

some_number = 3\n\n# Number is 3\nif some_number == 1:\n    print(\"Number is 1\")\nelif some_number == 2:\n    print(\"Number is 2\")\nelif some_number == 3:\n    print(\"Number is 3\")\nelse:\n    print(\"?\")\n

JavaScript (ES2015) / `if`

const someNumber = 3\n\n// Number is 3\nif (someNumber === 1) {\n  console.log('Number is 1')\n} else if (someNumber === 2) {\n  console.log('Number is 2')\n} else if (someNumber === 3) {\n  console.log('Number is 3')\n} else {\n  console.log('?')\n}

Control Flow: Ternary

Python 3

x = 2\ny = 3\n\n# even\nprint(\"even\" if x % 2 == 0 else \"odd\")\n# odd\nprint(\"even\" if y % 2 == 0 else \"odd\")\n

JavaScript (ES2015) / `Conditional Operator`

const x = 2\nconst y = 3\n\n// even\nconsole.log(x % 2 === 0 ? 'even' : 'odd')\n// odd\nconsole.log(y % 2 === 0 ? 'even' : 'odd')\n

Control Flow: Boolean

Python 3

# yes\nif \"abc\" == \"abc\":\n    print(\"yes\")\nelse:\n    print(\"no\")\n\n# yes\nif \"abc\" != \"def\":\n    print(\"yes\")\nelse:\n    print(\"no\")\n\n# no\nif True and False:\n    print(\"yes\")\nelse:\n    print(\"no\")\n\n# yes\nif True or False:\n    print(\"yes\")\nelse:\n    print(\"no\")\n\n# yes\nif not False:\n    print(\"yes\")\nelse:\n    print(\"no\")\n\n# no\nif 0:\n    print(\"yes\")\nelse:\n    print(\"no\")\n\n# no\nif \"\":\n    print(\"yes\")\nelse:\n    print(\"no\")\n\n# no\nif []:\n    print(\"yes\")\nelse:\n    print(\"no\")\n\n# no\nif None:\n    print(\"yes\")\nelse:\n    print(\"no\")\n\n# yes\nif not not not None:\n    print(\"yes\")\nelse:\n    print(\"no\")\n

JavaScript (ES2015) / `Falsy Values`

// yes\nif ('abc' === 'abc') {\n  console.log('yes')\n} else {\n  console.log('no')\n}\n\n// yes\nif ('abc' !== 'def') {\n  console.log('yes')\n} else {\n  console.log('no')\n}\n\n// no\nif (true && false) {\n  console.log('yes')\n} else {\n  console.log('no')\n}\n\n// yes\nif (true || false) {\n  console.log('yes')\n} else {\n  console.log('no')\n}\n\n// yes\nif (!false) {\n  console.log('yes')\n} else {\n  console.log('no')\n}\n\n// no\nif (0) {\n  console.log('yes')\n} else {\n  console.log('no')\n}\n\n// no\nif ('') {\n  console.log('yes')\n} else {\n  console.log('no')\n}\n\n// no\nif (undefined) {\n  console.log('yes')\n} else {\n  console.log('no')\n}\n\n// no\nif (null) {\n  console.log('yes')\n} else {\n  console.log('no')\n}\n\n// yes\nif (!!!null) {\n  console.log('yes')\n} else {\n  console.log('no')\n}\n

Control Flow: Exceptions

Python 3 / `Errors`

# foo is not defined\ntry:\n    foo()\nexcept NameError:\n    print(\"foo is not defined\")\n

JavaScript (ES2015) / `try...catch`

// foo is not defined\ntry {\n  foo()\n} catch (error) {\n  console.log('foo is not defined')\n}\n

Control Flow: Continue / Break

Python 3 / `break/continue`

# 1\n# 2\n# Fizz\n# 4\n# Buzz\nfor number in range(1, 101):\n    if number == 3:\n        print(\"Fizz\")\n        continue\n    if number == 5:\n        print(\"Buzz\")\n        break\n    print(number)\n

JavaScript (ES2015) / `continue`, `break`

// 1\n// 2\n// Fizz\n// 4\n// Buzz\nfor (let i = 1; i <= 100; i = i + 1) {\n  if (i === 3) {\n    console.log('Fizz')\n    continue\n  }\n\n  if (i === 5) {\n    console.log('Buzz')\n    break\n  }\n\n  console.log(i)\n}\n

String: Length

Python 3 / `len`

some_string = \"abcd\"\n\n# 4\nprint(len(some_string))\n

JavaScript (ES2015) / `length`

const someString = 'abcd'\n\n// 4\nconsole.log(someString.length)\n

String: Interpolation

Python 3

x = \"Hello\"\n\n# Hello World\nprint(f\"{x} World\")\n

JavaScript (ES2015)

const x = 'Hello'\n\n// Hello World\nconsole.log(`${x} World`)\n

String: Multiline

Python 3

x = \"\"\"------\nLine 1\nLine 2\nLine 3\n------\"\"\"\n\n# ------\n# Line 1\n# Line 2\n# Line 3\n# ------\nprint(x)\n

JavaScript (ES2015) / `Multiline Strings`

const x = `------\nLine 1\nLine 2\nLine 3\n------`\n\n// ------\n// Line 1\n// Line 2\n// Line 3\n// ------\nconsole.log(x)\n

String: String to Integer

Python 3 / `int`

string_1 = \"1\"\nnumber_1 = int(string_1)\n\n# 3\nprint(number_1 + 2)\n

JavaScript (ES2015) / `parseInt`

const string1 = '1'\nconst number1 = parseInt(string1)\n\n// 3\nconsole.log(number1 + 2)\n

String: Contains

Python 3 / `in`

# 2 is in the string\nif \"2\" in \"123\":\n    print(\"2 is in the string\")\n\n# 2 is not in the string\nif \"2\" not in \"456\":\n    print(\"2 is not in the string\")\n

JavaScript (ES2015) / `includes`

// 2 is in the string\nif ('123'.includes('2')) {\n  console.log('2 is in the string')\n}\n\n// 2 is not in the string\nif (!'456'.includes('2')) {\n  console.log('2 is not in the string')\n}\n

String: Substring

Python 3 / `[i:j]`

some_string = \"0123456\"\n\n# 234\nprint(some_string[2:5])\n

JavaScript (ES2015) / `substring`

const someString = '0123456'\n\n// 234\nconsole.log(someString.substring(2, 5))\n

String: Join

Python 3 / `join`

some_list = [\"a\", \"b\", \"c\"]\n\n# a,b,c\nprint(\",\".join(some_list))\n

JavaScript (ES2015) / `join`

const someList = ['a', 'b', 'c']\n\n// a,b,c\nconsole.log(someList.join(','))\n

String: Strip

Python 3 / `strip`

some_string = \"   abc   \"\n\n# abc\nprint(some_string.strip())\n

JavaScript (ES2015) / `trim`

const someString = '   abc   '\n\n// abc\nconsole.log(someString.trim())\n

String: Split

Python 3 / `split`

some_string = \"a,b,c\"\nsome_string_split = some_string.split(\",\")\n\n# a\nprint(some_string_split[0])\n# b\nprint(some_string_split[1])\n# c\nprint(some_string_split[2])\n

JavaScript (ES2015) / `split`

const someString = 'a,b,c'\nconst someStringSplit = someString.split(',')\n\n// a\nconsole.log(someStringSplit[0])\n// b\nconsole.log(someStringSplit[1])\n// c\nconsole.log(someStringSplit[2])\n

String: Replace

Python 3 / `replace`

some_string = \"a b c d e\"\n\n# a,b,c,d,e\nprint(some_string.replace(\" \", \",\"))\n

JavaScript (ES2015) / `Regular Expressions`, `replace`

const someString = 'a b c d e'\n\n// Only changes the first space\n// a,b c d e\n// console.log(someString.replace(' ', ','))\n\n// Use / /g instead of ' ' to change every space\nconsole.log(someString.replace(/ /g, ','))\n

String: Search

Python 3 / `search`

import re\n\n# Has a number\nif re.search(r\"\\d\", \"iphone 8\"):\n    print(\"Has a number\")\n\n# Doesn't have a number\nif not re.search(r\"\\d\", \"iphone x\"):\n    print(\"Doesn't have a number\")\n

JavaScript (ES2015) / `Regular Expressions`, `match`

// Has a number\nif ('iphone 8'.match(/\\d/g)) {\n  console.log('Has a number')\n}\n\n// Doesn't have a number\nif (!'iphone x'.match(/\\d/g)) {\n  console.log(\"Doesn't have a number\")\n}\n

List/Array: Iteration

Python 3

some_list = [6, 3, 5]\n\n# 6\n# 3\n# 5\nfor item in some_list:\n    print(item)\n

JavaScript (ES2015) / `forEach`

const someList = [6, 3, 5]\n\n// 6\n// 3\n// 5\nsomeList.forEach(element => {\n  console.log(element)\n})\n

List/Array: Length

Python 3 / `len`

some_list = [1, 4, 9]\n\n# 3\nprint(len(some_list))\n

JavaScript (ES2015) / `length`

const someList = [1, 4, 9]\n\n// 3\nconsole.log(someList.length)\n

List/Array: Enumerate

Python 3 / `enumerate`, `list`

some_list = [6, 3, 5]\n\n# 0 6\n# 1 3\n# 2 5\nfor i, item in enumerate(some_list):\n    print(f\"{i} {item}\")\n\n# If you're not using this in a for loop, use list()\n# list(enumerate(some_list)) # [(0, 6), (1, 3), (2, 5)]\n

JavaScript (ES2015) / `forEach`, `map`

const someList = [6, 3, 5]\n\n// 0 6\n// 1 3\n// 2 5\n\nsomeList.forEach((element, index) => {\n  console.log(`${index} ${element}`)\n})\n

List/Array: Contains

Python 3 / `in`

# 2 is in the list\nif 2 in [1, 2, 3]:\n    print(\"2 is in the list\")\n\n# 2 is not in the list\nif 2 not in [4, 5, 6]:\n    print(\"2 is not in the list\")\n

JavaScript (ES2015) / `includes`

// 2 is in the list\nif ([1, 2, 3].includes(2)) {\n  console.log('2 is in the list')\n}\n\n// 2 is not in the list\nif (![4, 5, 6].includes(2)) {\n  console.log('2 is not in the list')\n}\n

List/Array: Reverse

Python 3 / `reversed`, `list`

some_list = [1, 2, 3, 4]\n\n# reversed(some_list) is just an iterable.\n# To convert an iterable into a list, use list()\nreversed_list = list(reversed(some_list))\n\n# 4\n# 3\n# 2\n# 1\nfor item in reversed_list:\n    print(item)\n\n# You can use an iterable instead of a list in a for loop\n# for item in reversed(some_list):\n

JavaScript (ES2015) / `reverse`

const someList = [1, 2, 3, 4]\n\nsomeList.reverse()\n\n// 4\n// 3\n// 2\n// 1\nsomeList.forEach(element => {\n  console.log(element)\n})\n

List/Array: Range Iteration

Python 3 / `range`

# 0\n# 1\n# 2\n# 3\nfor i in range(4):\n    print(i)\n\n# 4\n# 5\n# 6\n# 7\nfor i in range(4, 8):\n    print(i)\n\n# 6\n# 5\n# 4\nfor i in range(6, 3, -1):\n    print(i)\n

JavaScript (ES2015)

// 0\n// 1\n// 2\n// 3\nfor (let i = 0; i < 4; i++) {\n  console.log(i)\n}\n\n// 4\n// 5\n// 6\n// 7\nfor (let i = 4; i < 8; i++) {\n  console.log(i)\n}\n\n// 6\n// 5\n// 4\nfor (let i = 6; i > 3; i--) {\n  console.log(i)\n}\n

List/Array: Append with Modification

Python 3 / `append`

some_list = [1, 2]\n\nsome_list.append(3)\n\n# 1\n# 2\n# 3\nfor x in some_list:\n    print(x)\n

JavaScript (ES2015) / `push`

const someList = [1, 2]\n\nsomeList.push(3)\n\n// 1\n// 2\n// 3\nsomeList.forEach(element => {\n  console.log(element)\n})\n

List/Array: Append without Modification

Python 3 / `Unpacking`

original_list = [1, 2]\n\n# [original_list, 3] -> [[1, 2], 3]\n# [*original_list, 3] -> [1, 2, 3]\nnew_list = [*original_list, 3]\noriginal_list[0] = 5\n\n# 1\n# 2\n# 3\nfor x in new_list:\n    print(x)\n

JavaScript (ES2015) / `Spread`

const originalList = [1, 2]\n\n// [originalList, 3] -> [[1, 2], 3]\n// [...originalList, 3] -> [1, 2, 3]\nconst newList = [...originalList, 3]\noriginalList[0] = 5\n\n// 1\n// 2\n// 3\nnewList.forEach(element => {\n  console.log(element)\n})\n

List/Array: Extend with Modification

Python 3 / `extend`

some_list = [1]\n\nsome_list.extend([2, 3])\n\n# 1\n# 2\n# 3\nfor x in some_list:\n    print(x)\n

JavaScript (ES2015) / `Spread`

const someList = [1]\n\nsomeList.push(...[2, 3])\n\n// 1\n// 2\n// 3\nsomeList.forEach(element => {\n  console.log(element)\n})\n

List/Array: Extend without Modification

Python 3 / `List addition`

original_list = [1]\nnew_list = original_list + [2, 3]\noriginal_list[0] = 5\n\n# 1\n# 2\n# 3\nfor x in new_list:\n    print(x)\n

JavaScript (ES2015) / `concat`

const originalList = [1]\nconst newList = originalList.concat([2, 3])\noriginalList[0] = 5\n\n// 1\n// 2\n// 3\nnewList.forEach(element => {\n  console.log(element)\n})\n

List/Array: Prepend

Python 3 / `insert`

some_list = [4, 5]\n\nsome_list.insert(0, 3)\n\n# 3\n# 4\n# 5\nfor x in some_list:\n    print(x)\n

JavaScript (ES2015) / `unshift`

const someList = [4, 5]\nsomeList.unshift(3)\n\n// 3\n// 4\n// 5\nsomeList.forEach(element => {\n  console.log(element)\n})\n

List/Array: Remove

Python 3 / `del`

some_list = [\"a\", \"b\", \"c\"]\ndel some_list[1]\n\n# a\n# c\nfor x in some_list:\n    print(x)\n

JavaScript (ES2015) / `splice`

const someList = ['a', 'b', 'c']\nsomeList.splice(1, 1)\n\n// a\n// c\nsomeList.forEach(element => {\n  console.log(element)\n})\n

List/Array: Pop

Python 3 / `pop`

some_list = [1, 2, 3, 4]\n\n# 4\nprint(some_list.pop())\n# 1\nprint(some_list.pop(0))\n\n# 2\n# 3\nfor x in some_list:\n    print(x)\n

JavaScript (ES2015) / `pop`, `shift`

const someList = [1, 2, 3, 4]\n\n// 4\nconsole.log(someList.pop())\n\n// 1\nconsole.log(someList.shift())\n\n// 2\n// 3\nsomeList.forEach(element => {\n  console.log(element)\n})\n

List/Array: Index

Python 3 / `index`

some_list = [\"a\", \"b\", \"c\", \"d\", \"e\"]\n\n# 2\nprint(some_list.index(\"c\"))\n

JavaScript (ES2015) / `indexOf`

const someList = ['a', 'b', 'c', 'd', 'e']\n\n// 2\nconsole.log(someList.indexOf('c'))\n

List/Array: Copy

Python 3 / `[i:j]`

original_list = [1, 2, 3]\nnew_list = original_list[:]  # or original_list.copy()\n\noriginal_list[2] = 4\n\n# 1\n# 2\n# 3\nfor x in new_list:\n    print(x)\n\n

JavaScript (ES2015) / `Spread`

const originalList = [1, 2, 3]\nconst newList = [...originalList]\n\noriginalList[2] = 4\n\n// 1\n// 2\n// 3\nnewList.forEach(element => {\n  console.log(element)\n})\n

List/Array: Map

Python 3 / `List Comprehensions`

original_list = [1, 2, 3]\nnew_list = [x * 2 for x in original_list]\n\n# 2\n# 4\n# 6\nfor x in new_list:\n    print(x)\n

JavaScript (ES2015) / `map`

const originalList = [1, 2, 3]\n\n// You can also do this:\n// const newList = originalList.map(x => { return x * 2 })\nconst newList = originalList.map(x => x * 2)\n\n// 2\n// 4\n// 6\nnewList.forEach(element => {\n  console.log(element)\n})\n

List/Array: Map (Nested)

Python 3 / `List Comprehensions`

first_list = [1, 3]\nsecond_list = [3, 4]\ncombined_list = [[x + y for y in second_list] for x in first_list]\n\n# 4\nprint(combined_list[0][0])\n# 5\nprint(combined_list[0][1])\n# 6\nprint(combined_list[1][0])\n# 7\nprint(combined_list[1][1])\n

JavaScript (ES2015) / `map`

const firstList = [1, 3]\nconst secondList = [3, 4]\n\nconst conbinedList = firstList.map(x => {\n  return secondList.map(y => {\n    return x + y\n  })\n})\n\n// 4\nconsole.log(conbinedList[0][0])\n// 5\nconsole.log(conbinedList[0][1])\n// 6\nconsole.log(conbinedList[1][0])\n// 7\nconsole.log(conbinedList[1][1])\n

List/Array: Filter

Python 3 / `List Comprehensions`

original_list = [1, 2, 3, 4, 5, 6]\nnew_list = [x for x in original_list if x % 2 == 0]\n\n# 2\n# 4\n# 6\nfor x in new_list:\n    print(x)\n

JavaScript (ES2015) / `filter`

const originalList = [1, 2, 3, 4, 5, 6]\nconst newList = originalList.filter(x => x % 2 == 0)\n\n// 2\n// 4\n// 6\nnewList.forEach(element => {\n  console.log(element)\n})\n

List/Array: Sum

Python 3 / `sum`

some_list = [1, 2, 3]\n\n# 6\nprint(sum(some_list))\n

JavaScript (ES2015) / `reduce`

const someList = [1, 2, 3]\nconst reducer = (accumulator, currentValue) => accumulator + currentValue\n\n// 6\nconsole.log(someList.reduce(reducer))\n

List/Array: Zip

Python 3 / `zip`

list_1 = [1, 3, 5]\nlist_2 = [2, 4, 6]\n\n# 1 2\n# 3 4\n# 5 6\nfor x, y in zip(list_1, list_2):\n    print(f\"{x} {y}\")\n

JavaScript (ES2015) / `map`

const list1 = [1, 3, 5]\nconst list2 = [2, 4, 6]\n\n// [[1, 2], [3, 4], [5, 6]]\nconst zippedList = list1.map((x, y) => {\n  return [x, list2[y]]\n})\n\nzippedList.forEach(element => {\n  console.log(`${element[0]} ${element[1]}`)\n})\n

List/Array: Slice

Python 3 / `[i:j]`

original_list = [\"a\", \"b\", \"c\", \"d\", \"e\"]\nnew_list = original_list[1:3]\noriginal_list[1] = \"x\"\n\n# b\n# c\nfor x in new_list:\n    print(x)\n

JavaScript (ES2015) / `slice`

const originalList = ['a', 'b', 'c', 'd', 'e']\nconst newList = originalList.slice(1, 3)\noriginalList[1] = 'x'\n\n// b\n// c\nnewList.forEach(element => {\n  console.log(element)\n})\n

List/Array: Sort

Python 3 / `sorted`

some_list = [4, 2, 1, 3]\n\n# 1\n# 2\n# 3\n# 4\nfor item in sorted(some_list):\n    print(item)\n

JavaScript (ES2015) / `sort`

const someList = [4, 2, 1, 3]\n\n// 1\n// 2\n// 3\n// 4\nsomeList.sort().forEach(element => {\n  console.log(element)\n})\n

List/Array: Sort Custom

Python 3 / `sorted`

some_list = [[\"c\", 2], [\"b\", 3], [\"a\", 1]]\n\n# a 1\n# c 2\n# b 3\nfor item in sorted(some_list, key=lambda x: x[1]):\n    print(f\"{item[0]} {item[1]}\")\n

JavaScript (ES2015) / `sort`

const someList = [['c', 2], ['b', 3], ['a', 1]]\n\n// a 1\n// c 2\n// b 3\nsomeList\n  .sort((a, b) => {\n    return a[1] - b[1]\n  })\n  .forEach(element => {\n    console.log(`${element[0]} ${element[1]}`)\n  })\n

Dictionary/Object: Iteration

Python 3 / `items`

some_dict = {\"one\": 1, \"two\": 2, \"three\": 3}\n\n# one 1\n# two 2\n# three 3\n# NOTE: If you're not using this in a for loop,\n# convert it into a list: list(some_dict.items())\nfor key, value in some_dict.items():\n    print(f\"{key} {value}\")\n

JavaScript (ES2015) / `entries`

const someDict = { one: 1, two: 2, three: 3 }\n\n// one 1\n// two 2\n// three 3\n\nObject.entries(someDict).forEach(element => {\n  console.log(`${element[0]} ${element[1]}`)\n})\n

Dictionary/Object: Contains

Python 3 / `in`

some_dict = {\"one\": 1, \"two\": 2, \"three\": 3}\n\n# one is in the dict\nif \"one\" in some_dict:\n    print(\"one is in the dict\")\n\n# four is not in the dict\nif \"four\" not in some_dict:\n    print(\"four is not in the dict\")\n

JavaScript (ES2015) / `hasOwnProperty`

const someDict = { one: 1, two: 2, three: 3 }\n\n// one is in the dict\nif (someDict.hasOwnProperty('one')) {\n  console.log('one is in the dict')\n}\n\n// four is not in the dict\nif (!someDict.hasOwnProperty('four')) {\n  console.log('four is not in the dict')\n}\n

Dictionary/Object: Add with Modification

Python 3

original_dict = {\"one\": 1, \"two\": 2}\noriginal_dict[\"three\"] = 3\n\n# one 1\n# two 2\n# three 3\nfor key, value in original_dict.items():\n    print(f\"{key} {value}\")\n\n

JavaScript (ES2015)

const originalDict = { one: 1, two: 2 }\noriginalDict.three = 3\n\n// one 1\n// two 2\n// three 3\nObject.entries(originalDict).forEach(element => {\n  console.log(`${element[0]} ${element[1]}`)\n})\n

Dictionary/Object: Add without Modification

Python 3 / `Unpacking`

original_dict = {\"one\": 1, \"two\": 2}\nnew_dict = {**original_dict, \"three\": 3}\noriginal_dict[\"one\"] = 100\n\n# one 1\n# two 2\n# three 3\nfor key, value in new_dict.items():\n    print(f\"{key} {value}\")\n

JavaScript (ES2015) / `Spread`

const originalDict = { one: 1, two: 2 }\nconst newDict = { ...originalDict, three: 3 }\noriginalDict.one = 100\n\n// one 1\n// two 2\n// three 3\nObject.entries(newDict).forEach(element => {\n  console.log(`${element[0]} ${element[1]}`)\n})\n

Dictionary/Object: Keys

Python 3 / `keys`

some_dict = {\"one\": 1, \"two\": 2, \"three\": 3}\n\n# one\n# two\n# three\n# NOTE: If you're not using this in a for loop,\n# convert it into a list: list(some_dict.keys())\nfor x in some_dict.keys():\n    print(x)\n

JavaScript (ES2015) / `keys`

const someDict = { one: 1, two: 2, three: 3 }\n\n// one\n// two\n// three\nObject.keys(someDict).forEach(element => {\n  console.log(element)\n})\n

Dictionary/Object: Values

Python 3 / `values`

some_dict = {\"one\": 1, \"two\": 2, \"three\": 3}\n\n\n# 1\n# 2\n# 3\n# NOTE: If you're not using this in a for loop,\n# convert it into a list: list(some_dict.values())\nfor x in some_dict.values():\n    print(x)\n

JavaScript (ES2015) / `values`

const someDict = { one: 1, two: 2, three: 3 }\n\n// 1\n// 2\n// 3\nObject.values(someDict).forEach(element => {\n  console.log(element)\n})\n

Dictionary/Object: Remove

Python 3 / `del`

some_dict = {\"one\": 1, \"two\": 2, \"three\": 3}\n\ndel some_dict[\"two\"]\n\n# one 1\n# three 3\nfor key, value in some_dict.items():\n    print(f\"{key} {value}\")\n

JavaScript (ES2015) / `delete`

const someDict = { one: 1, two: 2, three: 3 }\n\ndelete someDict.two\n\nObject.entries(someDict).forEach(element => {\n  console.log(`${element[0]} ${element[1]}`)\n})\n

Dictionary/Object: Get

Python 3 / `get`

some_dict = {\"one\": 1, \"two\": 2, \"three\": 3}\n\n# some_dict[\"four\"] will be KeyError\n\n# Doesn't exist\nprint(some_dict.get(\"five\", \"Doesn't exist\"))\n

JavaScript (ES2015) / `||`

const someDict = { one: 1, two: 2, three: 3 }\n\n// Doesn't exist\nconsole.log(someDict.five || \"Doesn't exist\")\n

Dictionary/Object: Map

Python 3 / `Dictionary Comprehensions`

original_list = {\"one\": 1, \"two\": 2}\n\n# {\"one\": 1, \"two\": 4}\nnew_list = {key: value * value for key, value in original_list.items()}\n\n# one 1\n# two 4\nfor key, value in new_list.items():\n    print(f\"{key} {value}\")\n

JavaScript (ES2015) / `entries`

const originalDict = { one: 1, two: 2 }\nconst newDict = {}\n\nObject.entries(originalDict).forEach(element => {\n  // newDict.element[0] doesn't work - for variable key use []\n  newDict[element[0]] = element[1] * element[1]\n})\n\n// one 1\n// two 4\nObject.entries(newDict).forEach(element => {\n  console.log(`${element[0]} ${element[1]}`)\n})\n

Dictionary/Object: Copy

Python 3 / `copy`

original_dict = {\"one\": 1, \"two\": 2, \"three\": 3}\nnew_dict = original_dict.copy()\noriginal_dict[\"one\"] = 100\n\n# one 1\n# two 2\n# three 3\nfor key, value in new_dict.items():\n    print(f\"{key} {value}\")\n

JavaScript (ES2015) / `Spread`

const originalDict = { one: 1, two: 2, three: 3 }\nconst newDict = { ...originalDict }\noriginalDict.one = 100\n\n// one 1\n// two 2\n// three 3\nObject.entries(newDict).forEach(element => {\n  console.log(`${element[0]} ${element[1]}`)\n})\n

Dictionary/Object: Dictionary/Object to JSON string

Python 3 / `json.dumps`

import json\n\nsome_dict = {\"one\": 1, \"two\": 2, \"three\": 3}\n\n# {\n#   \"one\": 1,\n#   \"two\": 2,\n#   \"three\": 3\n# }\nprint(json.dumps(some_dict, indent=2))\n

JavaScript (ES2015) / `JSON.stringify`

const someDict = { one: 1, two: 2, three: 3 }\n\n// {\n//   \"one\": 1,\n//   \"two\": 2,\n//   \"three\": 3\n// }\nconsole.log(JSON.stringify(someDict, null, 2))\n

Dictionary/Object: JSON string to Dictionary/Object

Python 3 / `json.loads`

import json\n\nsome_json = \"\"\"{\n  \"one\": 1,\n  \"two\": 2,\n  \"three\": 3\n}\"\"\"\n\ndict_from_json = json.loads(some_json)\n\n# 2\nprint(dict_from_json[\"two\"])\n

JavaScript (ES2015) / `JSON.parse`

const someJson = `{\n  \"one\": 1,\n  \"two\": 2,\n  \"three\": 3\n}`\n\nconst dictFromJson = JSON.parse(someJson)\n\n// 2\nconsole.log(dictFromJson.two)\n

Dictionary/Object: Variable Key

Python 3

some_variable = 2\nsome_dict = {(some_variable + 1): \"three\"}\n\n# three\nprint(some_dict[3])\n

JavaScript (ES2015) / `Computed Property Names`

const someVariable = 2\nconst someDict = { [someVariable + 1]: 'three' }\n\n// three\nconsole.log(someDict[3])\n

Function: Definitions

Python 3

def add(x, y):\n    print(f\"Adding {x} and {y}\")\n    return x + y\n\n\n# Adding 1 and 2\n# 3\nprint(add(1, 2))\n

JavaScript (ES2015)

const add = (x, y) => {\n  console.log(`Adding ${x} and ${y}`)\n  return x + y\n}\n// Adding 1 and 2\n// 3\nconsole.log(add(1, 2))\n

Function: Keyword Arguments

Python 3

def add(a, b, c):\n    return a + b + c\n\n\n# 6\nprint(add(b=1, a=2, c=3))\n

JavaScript (ES2015)

const add = ({ a, b, c }) => {\n  return a + b + c\n}\n\n// 6\nconsole.log(\n  add({\n    b: 1,\n    a: 2,\n    c: 3\n  })\n)\n

Function: Default Arguments

Python 3

def greet(name, word=\"Hello\"):\n    print(f\"{word} {name}\")\n\n\n# Hello World\ngreet(\"World\")\n\n# Goodbye World\ngreet(\"World\", \"Goodbye\")\n

JavaScript (ES2015) / `Default Parameters`

const greet = (name, word = 'Hello') => {\n  console.log(`${word} ${name}`)\n}\n\n// Hello World\ngreet('World')\n\n// Goodbye World\ngreet('World', 'Goodbye')\n

Function: Default Keyword Arguments

Python 3

def greet(name=\"World\", word=\"Hello\"):\n    print(f\"{word} {name}\")\n\n\n# Goodbye World\ngreet(word=\"Goodbye\")\n\n# Hello Programming\ngreet(name=\"Programming\")\n

JavaScript (ES2015) / `Default Value`

const greet = ({ name = 'World', word = 'Hello' }) => {\n  console.log(`${word} ${name}`)\n}\n\n// Goodbye World\ngreet({ word: 'Goodbye' })\n\n// Hello Programming\ngreet({ name: 'Programming' })\n

Function: Positional Arguments

Python 3 / `Arbitrary Argument Lists`

def positional_args(a, b, *args):\n    print(a)\n    print(b)\n    for x in args:\n        print(x)\n\n\n# 1\n# 2\n# 3\n# 4\npositional_args(1, 2, 3, 4)\n

JavaScript (ES2015) / `Rest Parameters`

const positionalArgs = (a, b, ...args) => {\n  console.log(a)\n  console.log(b)\n  args.forEach(element => {\n    console.log(element)\n  })\n}\n\n// 1\n// 2\n// 3\n// 4\npositionalArgs(1, 2, 3, 4)\n

Function: Variable Keyword Arguments

Python 3 / `Keyword Arguments`

def func_1(**kwargs):\n    for key, value in kwargs.items():\n        print(f\"{key} {value}\")\n\n\ndef func_2(x, *args, **kwargs):\n    print(x)\n    for arg in args:\n        print(arg)\n    for key, value in kwargs.items():\n        print(f\"{key} {value}\")\n\n\n# one 1\n# two 2\nfunc_1(one=1, two=2)\n\n# 1\n# 2\n# 3\n# a 4\n# b 5\nfunc_2(1, 2, 3, a=4, b=5)\n

JavaScript (ES2015) / `Rest Parameters`

const func1 = kwargs => {\n  Object.entries(kwargs).forEach(element => {\n    console.log(`${element[0]} ${element[1]}`)\n  })\n}\n\n//  ...args must be the last argument\nconst func2 = (x, kwargs, ...args) => {\n  console.log(x)\n  args.forEach(element => {\n    console.log(element)\n  })\n  Object.entries(kwargs).forEach(element => {\n    console.log(`${element[0]} ${element[1]}`)\n  })\n}\n\n// one 1\n// two 2\nfunc1({ one: 1, two: 2 })\n\n// 1\n// 2\n// 3\n// a 4\n// b 5\nfunc2(1, { a: 4, b: 5 }, 2, 3)\n

Class: Basics

Python 3 / `Classes`

class Duck:\n    def __init__(self, name):\n        self.name = name\n\n    def fly(self):\n        print(f\"{self.name} can fly\")\n\n    # not @classmethod: call a method on an instance\n    # duck = Duck(...)\n    # duck.create(...)\n    #\n    # @classmethod: call a method on a class\n    # Duck.create(...)\n    @classmethod\n    def create(cls, name, kind):\n        if kind == \"mallard\":\n            return MallardDuck(name)\n        elif kind == \"rubber\":\n            return RubberDuck(name)\n        else:\n            # cls = Duck\n            return cls(name)\n\n\nclass MallardDuck(Duck):\n    # @property:\n    # use duck.color instead of duck.color()\n    @property\n    def color(self):\n        return \"green\"\n\n\nclass RubberDuck(Duck):\n    def __init__(self, name, eye_color=\"black\"):\n        super().__init__(name)\n        self.eye_color = eye_color\n\n    def fly(self):\n        super().fly()\n        print(f\"Just kidding, {self.name} cannot fly\")\n\n    @property\n    def color(self):\n        return \"yellow\"\n\n\nregularDuck = Duck(\"reggie\")\n# reggie can fly\nregularDuck.fly()\n\nmallardDuck = Duck.create(\"mal\", \"mallard\")\n# mal\nprint(mallardDuck.name)\n# green\nprint(mallardDuck.color)\n\nrubberDuck = RubberDuck(\"vic\", \"blue\")\n# vic can fly\n# Just kidding, vic cannot fly\nrubberDuck.fly()\n# yellow\nprint(rubberDuck.color)\n# blue\nprint(rubberDuck.eye_color)\n

JavaScript (ES2015) / `Classes`, `Method Definitions`, `static`, `get`, `super`

class Duck {\n  constructor(name) {\n    this.name = name\n  }\n\n  fly() {\n    console.log(`${this.name} can fly`)\n  }\n\n  // not static: call a method on an instance\n  // const duck = new Duck(...)\n  // duck.create(...)\n  //\n  // static: call a method on a class\n  // Duck.create(...)\n  static create(name, kind) {\n    if (kind === 'mallard') {\n      return new MallardDuck(name)\n    } else if (kind === 'rubber') {\n      return new RubberDuck(name)\n    } else {\n      // this = Duck\n      return new this(name)\n    }\n  }\n}\n\nclass MallardDuck extends Duck {\n  // get:\n  // use duck.color instead of duck.color()\n  get color() {\n    return 'green'\n  }\n}\n\nclass RubberDuck extends Duck {\n  constructor(name, eyeColor = 'black') {\n    super(name)\n    this.eyeColor = eyeColor\n  }\n\n  fly() {\n    super.fly()\n    console.log(`Just kidding, ${this.name} cannot fly`)\n  }\n\n  get color() {\n    return 'yellow'\n  }\n}\n\nconst regularDuck = new Duck('reggie')\n// reggie can fly\nregularDuck.fly()\n\nconst mallardDuck = Duck.create('mal', 'mallard')\n// mal\nconsole.log(mallardDuck.name)\n// green\nconsole.log(mallardDuck.color)\n\nrubberDuck = new RubberDuck('vic', 'blue')\n// vic can fly\n// Just kidding, vic cannot fly\nrubberDuck.fly()\n\n// yellow\nconsole.log(rubberDuck.color)\n\n// blue\nconsole.log(rubberDuck.eyeColor)\n

\n How to write X in both Python 3 and JavaScript (ES2015)\n

About the Author

Table of Contents

Math: Absolute Value

Python 3 / abs

JavaScript (ES2015) / abs

Math: Round Numbers

Python 3 / ceil, floor, round

JavaScript (ES2015) / ceil, floor, round

Math: Max and Min

Python 3 / max, min

JavaScript (ES2015) / max, min

Control Flow: If else

Python 3 / if

JavaScript (ES2015) / if

Control Flow: Ternary

Python 3

JavaScript (ES2015) / Conditional Operator

Control Flow: Boolean

Python 3

JavaScript (ES2015) / Falsy Values

Control Flow: Exceptions

Python 3 / Errors

JavaScript (ES2015) / try...catch

Control Flow: Continue / Break

Python 3 / break/continue

JavaScript (ES2015) / continue, break

String: Length

Python 3 / len

JavaScript (ES2015) / length

String: Interpolation

Python 3

JavaScript (ES2015)

String: Multiline

Python 3

JavaScript (ES2015) / Multiline Strings

String: String to Integer

Python 3 / int

JavaScript (ES2015) / parseInt

String: Contains

Python 3 / in

JavaScript (ES2015) / includes

String: Substring

Python 3 / [i:j]

JavaScript (ES2015) / substring

String: Join

Python 3 / join

JavaScript (ES2015) / join

String: Strip

Python 3 / strip

JavaScript (ES2015) / trim

String: Split

Python 3 / split

JavaScript (ES2015) / split

String: Replace

Python 3 / replace

JavaScript (ES2015) / Regular Expressions, replace

String: Search

Python 3 / search

JavaScript (ES2015) / Regular Expressions, match

List/Array: Iteration

Python 3

JavaScript (ES2015) / forEach

List/Array: Length

Python 3 / len

JavaScript (ES2015) / length

List/Array: Enumerate

Python 3 / enumerate, list

JavaScript (ES2015) / forEach, map

List/Array: Contains

Python 3 / in

JavaScript (ES2015) / includes

List/Array: Reverse

Python 3 / reversed, list

JavaScript (ES2015) / reverse

List/Array: Range Iteration

Python 3 / range

JavaScript (ES2015)

List/Array: Append with Modification

Python 3 / append

Python 3 / `abs`

JavaScript (ES2015) / `abs`

Python 3 / `ceil`, `floor`, `round`

JavaScript (ES2015) / `ceil`, `floor`, `round`

Python 3 / `max`, `min`

JavaScript (ES2015) / `max`, `min`

Python 3 / `if`

JavaScript (ES2015) / `if`

JavaScript (ES2015) / `Conditional Operator`

JavaScript (ES2015) / `Falsy Values`

Python 3 / `Errors`

JavaScript (ES2015) / `try...catch`

Python 3 / `break/continue`

JavaScript (ES2015) / `continue`, `break`

Python 3 / `len`

JavaScript (ES2015) / `length`

JavaScript (ES2015) / `Multiline Strings`

Python 3 / `int`

JavaScript (ES2015) / `parseInt`

Python 3 / `in`

JavaScript (ES2015) / `includes`

Python 3 / `[i:j]`

JavaScript (ES2015) / `substring`

Python 3 / `join`

JavaScript (ES2015) / `join`

Python 3 / `strip`

JavaScript (ES2015) / `trim`

Python 3 / `split`

JavaScript (ES2015) / `split`

Python 3 / `replace`

JavaScript (ES2015) / `Regular Expressions`, `replace`

Python 3 / `search`

JavaScript (ES2015) / `Regular Expressions`, `match`

JavaScript (ES2015) / `forEach`

Python 3 / `len`

JavaScript (ES2015) / `length`

Python 3 / `enumerate`, `list`

JavaScript (ES2015) / `forEach`, `map`

Python 3 / `in`

JavaScript (ES2015) / `includes`

Python 3 / `reversed`, `list`

JavaScript (ES2015) / `reverse`

Python 3 / `range`

Python 3 / `append`

JavaScript (ES2015) / `push`

Python 3 / `Unpacking`

JavaScript (ES2015) / `Spread`

Python 3 / `extend`

JavaScript (ES2015) / `Spread`

Python 3 / `List addition`

JavaScript (ES2015) / `concat`

Python 3 / `insert`

JavaScript (ES2015) / `unshift`

Python 3 / `del`

JavaScript (ES2015) / `splice`

Python 3 / `pop`

JavaScript (ES2015) / `pop`, `shift`

Python 3 / `index`

JavaScript (ES2015) / `indexOf`

Python 3 / `[i:j]`

JavaScript (ES2015) / `Spread`

Python 3 / `List Comprehensions`

JavaScript (ES2015) / `map`

Python 3 / `List Comprehensions`

JavaScript (ES2015) / `map`

Python 3 / `List Comprehensions`

JavaScript (ES2015) / `filter`

Python 3 / `sum`

JavaScript (ES2015) / `reduce`

Python 3 / `zip`

JavaScript (ES2015) / `map`

Python 3 / `[i:j]`

JavaScript (ES2015) / `slice`

Python 3 / `sorted`

JavaScript (ES2015) / `sort`

Python 3 / `sorted`

JavaScript (ES2015) / `sort`

Python 3 / `items`

JavaScript (ES2015) / `entries`

Python 3 / `in`