Most of you probably already know them. lodash/underscore was built to provide utility functions for common tasks in Javascript. But some you don’t want to install a package for the small use case.
Repo: Javascript Quick functions
Table of contents
- Regular function
- Function expression
- Arrow function
- Generator function
- Time the execution of your code
- Evaluate a string
- Create an array of numbers from 1 to n
- Create an array of numbers from 1 to n with a step
- Create an array and fill it with a value
- Shuffling an array
- Convert an object into a list of
[key, value]pairs - Convert a list of
[key, value]pairs into an object - Remove an element from an array
- Remove Duplicated from Array
- Swap variables or values
- Generate random number
- Generate random number with a step
- Number is even or not
- Number is odd or not
- Find the factorial of a number
- Find the sum of an array
- Find median of an array
- Find largest numbers
- Find average of Numbers
- Find smallest numbers
- Find mode of an array
- Find the range of an array
- Pick a random element from an array
- Map an array without .map()
- Empty an array without .splice()
- Convert array to object
- Find intersection of two arrays
- Remove falsy values from an array
- Rounding number to N decimal place
- Reverse String
- Find Longest Word in a String
- Generate Title Case
- Is String Palindrome
- Copy to Clipboard
- Find a vowel in a string
- Email validator
- Validate only character and space
- Validate only number
- Casting values in arrays using map
- Check object is empty or not
- Get the current date
- Find the day of the week
- Find the day of the year
- Find the number of days in a month
- Find the current month
- Find the number of seconds until midnight
- Log Time from Date
- Format JSON output with spaces
- Deep clone an object
Functions
Regular function
function sum(a, b) {
return a + b;
}
Function expression
const sum = function (a, b) {
return a + b;
};
Arrow function
const sum = (a, b) => {
return a + b;
};
// OR
const sum = (a, b) => a + b;
Generator function
function* indexGenerator() {
let index = 0;
while (true) {
yield index++;
}
}
const g = indexGenerator();
console.log(g.next().value); // => 0
console.log(g.next().value); // => 1
Time the execution of your code
console.time("time");
for (let i = 0; i < 1000000; i++) {
// do something
}
console.timeEnd("time"); // time: 0.827ms
Evaluate a string
const toJavascript = (str) => eval(str);
toJavascript("alert('Hello World')");
Array
Create an array of numbers from 1 to n
const range = (n) => Array.from({ length: n }, (_, i) => i + 1);
console.log(range(10)); // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Create an array of numbers from 1 to n with a step
const range = (n, step = 1) => Array.from({ length: n }, (_, i) => i * step);
console.log(range(10, 2)); // [1, 3, 5, 7, 9]
Create an array and fill it with a value
const fill = (len, value) => Array(len).fill(value);
console.log(fill(3, 0)); // [0, 0, 0]
Shuffling an array
const shuffleArray = (arr) => arr.sort(() => 0.5 - Math.random());
console.log(shuffleArray([1, 2, 3, 4])); // [3, 2, 1, 4]
Convert an object into a list of [key, value] pairs
const toPairs = (obj) => Object.entries(obj);
console.log(toPairs({ a: 1, b: 2, c: 3 })); // [['a', 1], ['b', 2], ['c', 3]]
Convert a list of [key, value] pairs into an object
const fromPairs = (pairs) =>
pairs.reduce((a, b) => ({ ...a, [b[0]]: b[1] }), {});
console.log(
fromPairs([
["a", 1],
["b", 2],
["c", 3],
])
); // { a: 1, b: 2, c: 3 }
Remove an element from an array
const removeElement = (arr, element) => arr.filter((e) => e !== element);
console.log(removeElement([1, 2, 3, 4], 2)); // [1, 3, 4]
Remove Duplicated from Array
const removeDuplicated = (arr) => [...new Set(arr)];
console.log(removeDuplicated([1, 2, 3, 3, 4, 4, 5, 5, 6])); // Result: [ 1, 2, 3, 4, 5, 6 ]
const removeDuplicate = (arr) =>
Object.values(arr.reduce((a, b) => (a[b] ? a : { ...a, [b]: b }), {}));
console.log(removeDuplicate([1, 2, 3, 3])); // Result: [ 1, 2, 3, ]
Swap variables or values
const swap = (a, b) => [b, a];
let a = 1,
b = 2;
[b, a] = swap(a, b);
console.log(a, b); // 2, 1
Numbers
Generate random number
const random = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;
console.log(random(1, 10)); // Result: 1 ~ 10
Generate random number with a step
const random = (min, max, step = 1) =>
Math.floor(Math.random() * (max - min + 1)) * step + min;
console.log(random(1, 10, 2)); // Result: 1 ~ 10 with step 2
Number is even or not
const isEven = (num) => num % 2 === 0;
console.log(isEven(4)); // true
Number is odd or not
const isOdd = (num) => num % 2 !== 0;
console.log(isOdd(4)); // false
Find the factorial of a number
const factorial = (num) => (num === 0 ? 1 : num * factorial(num - 1));
console.log(factorial(5)); // 120
Find the sum of an array
const sum = (arr) => arr.reduce((a, b) => a + b, 0);
console.log(sum([1, 2, 3, 4])); // 10
Find median of an array
const median = (arr) => {
const mid = Math.floor(arr.length / 2),
nums = [...arr].sort((a, b) => a - b);
return arr.length % 2 !== 0 ? nums[mid] : (nums[mid - 1] + nums[mid]) / 2;
};
console.log(median([1, 2, 3, 4])); // 2.5
Find largest numbers
const findLargest = (arr) => arr.map((subArr) => Math.max(...subArr));
console.log(
findLargest([
[4, 5, 1, 3],
[13, 27, 18, 26],
[32, 35, 37, 39],
[1000, 1001, 857, 1],
])
); // [5, 27, 39, 1001]
Find average of Numbers
const findAverage = (arr) => arr.reduce((a, b) => a + b, 0) / arr.length;
console.log(findAverage([1, 2, 3, 4])); // 2.5
Find smallest numbers
const findSmallest = (arr) => arr.map((subArr) => Math.min(...subArr));
console.log(
findSmallest([
[4, 5, 1, 3],
[13, 27, 18, 26],
[32, 35, 37, 39],
[1000, 1001, 857, 1],
])
); // [1, 18, 32, 857]
Find mode of an array
const mode = (arr) => {
const counts = arr.reduce((a, b) => {
a[b] = (a[b] || 0) + 1;
return a;
}, {});
const maxCount = Math.max(...Object.values(counts));
return Object.keys(counts).filter((key) => counts[key] === maxCount);
};
console.log(mode([3, "a", "a", "a", 2, 3, "a", 3, "a", 2, 4, 9, 3])); // ['a']
Find the range of an array
const range = (arr) => Math.max(...arr) - Math.min(...arr);
console.log(range([1, 2, 3, 4])); // 3
Pick a random element from an array
const pick = (arr) => arr[Math.floor(Math.random() * arr.length)];
console.log(pick([1, 2, 3, 4])); // 2
Map an array without .map()
const map = (arr, cb) => Array.from(arr, cb);
console.log(map([1, 2, 3, 4], (n) => n * 2)); // [2, 4, 6, 8]
Empty an array without .splice()
const empty = (arr) => {
arr.length = 0;
return arr;
};
console.log(empty([1, 2, 3, 4])); // []
Convert array to object
const toObject = (arr) => ({ ...arr });
console.log(toObject(["a", "b"])); // { 0: 'a', 1: 'b' }
Find intersection of two arrays
const intersection = (arr1, arr2) => {
const set = new Set(arr1);
return arr2.filter((x) => set.has(x));
};
console.log(intersection([1, 2, 3], [2, 3, 4])); // [2, 3]
Remove falsy values from an array
const compact = (arr) => arr.filter(Boolean);
console.log(compact([0, 1, false, 2, "", 3, "a", "e" * 23, NaN, "s", 34])); // [1, 2, 3, 'a', 's', 34]
Rounding number to N decimal place
const round = (num, decimals = 0) => num.toFixed(decimals);
console.log(round(1.005, 2)); // 1.00
String
Reverse String
const reverseString = (str) => str.split("").reverse().join("");
console.log(reverseString("hello")); // olleh
Find Longest Word in a String
const findLongestWord = (str) =>
str.split(" ").reduce((a, b) => (a.length > b.length ? a : b));
console.log(findLongestWord("The quick brown fox jumped over the lazy dog")); // jumped
Generate Title Case
const titleCase = (str) =>
str
.split(" ")
.map((word) => word[0].toUpperCase() + word.slice(1).toLowerCase())
.join(" ");
console.log(titleCase("the quick brown fox")); // The Quick Brown Fox
Is String Palindrome
const isPalindrome = (str) => str === str.split("").reverse().join("");
console.log(isPalindrome("madam")); // true
Copy to Clipboard
const copyToClipboard = (text) => navigator.clipboard.writeText(text);
copyToClipboard("Hello World");
Find a vowel in a string
const findVowel = (str) => str.match(/[aeiou]/gi);
console.log(findVowel("hello")); // ['e', 'o']
Email validator
const validateEmail = (email) => {
const re = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
return re.test(String(email).toLowerCase());
};
console.log(validateEmail('abc@aaa.co'); // true
Validate only character and space
const validateName = (name) => /^[A-Za-z\s]+$/.test(name);
console.log(validateName("abc")); // true
console.log(validateName("123")); // false
Validate only number
const validateNumber = (number) => /^[0-9]+$/.test(number);
console.log(validateNumber("123")); // true
console.log(validateNumber("abc")); // false
Casting values in arrays using map
const castArray = (arr) => arr.map(Number);
console.log(castArray(["1", "2", [3]])); // [1, 2, 3]
Date & Object
Check object is empty or not
const isEmpty = (obj) => Object.keys(obj).length === 0;
console.log(isEmpty({})); // true
Get the current date
const getDate = () => new Date();
console.log(getDate()); // 2020-05-25T09:57:37.869Z
Find the day of the week
const getDayName = (date) => {
const days = [
"Sunday",
"Monday",
"Tuesday",
"Wednesday",
"Thursday",
"Friday",
"Saturday",
];
return days[date.getDay()];
};
console.log(getDayName(new Date())); // Friday
Find the day of the year
const getDayOfYear = (date) => {
const firstDay = new Date(date.getFullYear(), 0, 1);
return Math.ceil((date - firstDay) / 86400000);
};
console.log(getDayOfYear(new Date())); // 182
Find the number of days in a month
const getDaysInMonth = (date) =>
new Date(date.getFullYear(), date.getMonth() + 1, 0).getDate();
console.log(getDaysInMonth(new Date())); // 31
Find the current month
const getMonthName = (date) => {
const months = [
"January",
"February",
"March",
"April",
"May",
"June",
"July",
"August",
"September",
"October",
"November",
"December",
];
return months[date.getMonth()];
};
console.log(getMonthName(new Date())); // March
Find the number of seconds until midnight
const getSecondsUntilMidnight = (date) =>
(24 - date.getHours()) * 60 * 60 +
(60 - date.getMinutes()) * 60 +
(60 - date.getSeconds());
console.log(getSecondsUntilMidnight(new Date())); // 86400
Log Time from Date
const logTime = (date) => date.toTimeString().slice(0, 8);
logTime(new Date()); // 09:57:37
const logTime = (date) => date.toLocaleTimeString("en-GB");
logTime(new Date()); // 09:57:37
Format JSON output with spaces
const formatJSON = (json) => JSON.stringify(json, null, 2);
console.log(formatJSON({ a: 1, b: 2 }));
Deep clone an object
const clone = (obj) => JSON.parse(JSON.stringify(obj));
console.log(clone({ a: 1, b: 2 })); // { a: 1, b: 2 }
// OR
const deepCopy = (obj, copy = {}) => {
if (!obj || typeof obj !== "object") return obj;
for (const key in obj) {
if (obj.hasOwnProperty(key)) copy[key] = deepCopy(obj[key]);
}
return copy;
};
Promises
Wait for a promise to resolve
const wait = (ms) => new Promise((resolve) => setTimeout(resolve, ms));
wait(1000).then(() => console.log("You'll see this after 1 second"));
await wait(1000); // Next line will be executed after 1 second
Is function async
const isAsync = (fn) => fn.constructor.name === "AsyncFunction";
console.log(isAsync(async () => {})); // true
Callback to Promise
const promisify =
(fn) =>
(...args) => {
return new Promise((res, reject) =>
fn(...args, (err, data) => (err ? reject(err) : res(data)))
);
};
Promise retry
const retry = (fn, times = 3) => {
return (...args) =>
new Promise((resolve, reject) => {
const attempt = (n) => {
fn(...args)
.then(resolve)
.catch((err) => {
if (n === times) return reject(err);
attempt(n + 1);
});
};
attempt(1);
});
};
Styling
Generate a random color
const getRandomColor = () =>
`#${Math.floor(Math.random() * 16777215).toString(16)}`;
console.log(getRandomColor()); // #f0f0f0
const randomHex = () =>
`#${Math.floor(Math.random() * 0xffffff)
.toString(16)
.padEnd(6, "0")}`;
console.log(randomHex()); // #f0f0f0
Convert to rem
const toRem = (px) => `${px / 16}rem`;
console.log(toRem(16)); // 1rem
Styled Components get color from theme
Off topic but very useful
const getPrimaryMain = props => props.theme.main
const Button = styled.button`
color: ${getPrimaryMain};
border: 2px solid ${getPrimaryMain};
`;
Window & Dom
Get selected text
const getSelectedText = () => window.getSelection().toString();
console.log(getSelectedText()); // Hello World
Data Structures
Create a stack
const Stack = () => {
let data = [];
return {
push(item) {
data.push(item);
},
pop() {
return data.pop();
},
peek() {
return data[data.length - 1];
},
get length() {
return data.length;
},
};
};
Create a queue
const Queue = () => {
let data = [];
return {
push(item) {
data.push(item);
},
pop() {
return data.shift();
},
peek() {
return data[0];
},
get length() {
return data.length;
},
};
};
Recursion
const range = (n) => {
if (n === 0) return;
console.log(n);
range(n - 1);
};
console.log(range(5));
Memoization (cache)
Try the following code without memo and with memo.
const fib = (n) => {
if (n < 2) return n;
return fib(n - 1, memo) + fib(n - 2, memo);
};
console.log(fib(40)); // Browser crash or timeout
const fib = (n, memo = {}) => {
if (n < 2) return n;
if (memo[n]) return memo[n];
memo[n] = fib(n - 1, memo) + fib(n - 2, memo);
return memo[n];
};
console.log(fib(40)); // 102334155
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