These snippets, while useful and interesting, didn't quite make it into the repository due to either having very specific use-cases or being outdated. However we felt like they might still be useful to some readers, so here they are.
JSONToDatebinarySearchcelsiusToFahrenheitcleanObjcollatzcountVowelsfactorsfahrenheitToCelsiusfibonacciCountUntilNumfibonacciUntilNumheronAreahowManyTimeshttpDeletehttpPutisArmstrongNumberisSimilarkmphToMphlevenshteinDistancemphToKmphpipeLogquickSortremoveVowelssolveRPNspeechSynthesissquareSum
Converts a JSON object to a date.
Use Date(), to convert dates in JSON format to readable format (dd/mm/yyyy).
const JSONToDate = arr => {
const dt = new Date(parseInt(arr.toString().substr(6)));
return `${dt.getDate()}/${dt.getMonth() + 1}/${dt.getFullYear()}`;
};Examples
JSONToDate(/Date(1489525200000)/); // "14/3/2017"Use recursion. Similar to Array.prototype.indexOf() that finds the index of a value within an array.
The difference being this operation only works with sorted arrays which offers a major performance boost due to it's logarithmic nature when compared to a linear search or Array.prototype.indexOf().
Search a sorted array by repeatedly dividing the search interval in half.
Begin with an interval covering the whole array.
If the value of the search is less than the item in the middle of the interval, recurse into the lower half. Otherwise recurse into the upper half.
Repeatedly recurse until the value is found which is the mid or you've recursed to a point that is greater than the length which means the value doesn't exist and return -1.
const binarySearch = (arr, val, start = 0, end = arr.length - 1) => {
if (start > end) return -1;
const mid = Math.floor((start + end) / 2);
if (arr[mid] > val) return binarySearch(arr, val, start, mid - 1);
if (arr[mid] < val) return binarySearch(arr, val, mid + 1, end);
return mid;
};Examples
binarySearch([1, 4, 6, 7, 12, 13, 15, 18, 19, 20, 22, 24], 6); // 2
binarySearch([1, 4, 6, 7, 12, 13, 15, 18, 19, 20, 22, 24], 21); // -1Celsius to Fahrenheit temperature conversion.
Follows the conversion formula F = 1.8C + 32.
const celsiusToFahrenheit = degrees => 1.8 * degrees + 32;Examples
celsiusToFahrenheit(33) // 91.4Removes any properties except the ones specified from a JSON object.
Use Object.keys() method to loop over given JSON object and deleting keys that are not included in given array.
If you pass a special key,childIndicator, it will search deeply apply the function to inner objects, too.
const cleanObj = (obj, keysToKeep = [], childIndicator) => {
Object.keys(obj).forEach(key => {
if (key === childIndicator) {
cleanObj(obj[key], keysToKeep, childIndicator);
} else if (!keysToKeep.includes(key)) {
delete obj[key];
}
});
return obj;
};Examples
const testObj = { a: 1, b: 2, children: { a: 1, b: 2 } };
cleanObj(testObj, ['a'], 'children'); // { a: 1, children : { a: 1}}Applies the Collatz algorithm.
If n is even, return n/2. Otherwise, return 3n+1.
const collatz = n => (n % 2 === 0 ? n / 2 : 3 * n + 1);Examples
collatz(8); // 4Retuns number of vowels in provided string.
Use a regular expression to count the number of vowels (A, E, I, O, U) in a string.
const countVowels = str => (str.match(/[aeiou]/gi) || []).length;Examples
countVowels('foobar'); // 3
countVowels('gym'); // 0Returns the array of factors of the given num.
If the second argument is set to true returns only the prime factors of num.
If num is 1 or 0 returns an empty array.
If num is less than 0 returns all the factors of -int together with their additive inverses.
Use Array.from(), Array.prototype.map() and Array.prototype.filter() to find all the factors of num.
If given num is negative, use Array.prototype.reduce() to add the additive inverses to the array.
Return all results if primes is false, else determine and return only the prime factors using isPrime and Array.prototype.filter().
Omit the second argument, primes, to return prime and non-prime factors by default.
Note:- Negative numbers are not considered prime.
const factors = (num, primes = false) => {
const isPrime = num => {
const boundary = Math.floor(Math.sqrt(num));
for (var i = 2; i <= boundary; i++) if (num % i === 0) return false;
return num >= 2;
};
const isNeg = num < 0;
num = isNeg ? -num : num;
let array = Array.from({ length: num - 1 })
.map((val, i) => (num % (i + 2) === 0 ? i + 2 : false))
.filter(val => val);
if (isNeg)
array = array.reduce((acc, val) => {
acc.push(val);
acc.push(-val);
return acc;
}, []);
return primes ? array.filter(isPrime) : array;
};Examples
factors(12); // [2,3,4,6,12]
factors(12, true); // [2,3]
factors(-12); // [2, -2, 3, -3, 4, -4, 6, -6, 12, -12]
factors(-12, true); // [2,3]Fahrenheit to Celsius temperature conversion.
Follows the conversion formula C = (F - 32) * 5/9.
const fahrenheitToCelsius = degrees => (degrees - 32) * 5/9;Examples
fahrenheitToCelsius(32); // 0Returns the number of fibonnacci numbers up to num(0 and num inclusive).
Use a mathematical formula to calculate the number of fibonacci numbers until num.
const fibonacciCountUntilNum = num =>
Math.ceil(Math.log(num * Math.sqrt(5) + 1 / 2) / Math.log((Math.sqrt(5) + 1) / 2));Examples
fibonacciCountUntilNum(10); // 7Generates an array, containing the Fibonacci sequence, up until the nth term.
Create an empty array of the specific length, initializing the first two values (0 and 1).
Use Array.prototype.reduce() to add values into the array, using the sum of the last two values, except for the first two.
Uses a mathematical formula to calculate the length of the array required.
const fibonacciUntilNum = num => {
let n = Math.ceil(Math.log(num * Math.sqrt(5) + 1 / 2) / Math.log((Math.sqrt(5) + 1) / 2));
return Array.from({ length: n }).reduce(
(acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i),
[]
);
};Examples
fibonacciUntilNum(10); // [ 0, 1, 1, 2, 3, 5, 8 ]Returns the area of a triangle using only the 3 side lengths, Heron's formula. Assumes that the sides define a valid triangle. Does NOT assume it is a right triangle.
More information on what Heron's formula is and why it works available here: https://en.wikipedia.org/wiki/Heron%27s_formula.
Uses Math.sqrt() to find the square root of a value.
const heronArea = (side_a, side_b, side_c) => {
const p = (side_a + side_b + side_c) / 2
return Math.sqrt(p * (p-side_a) * (p-side_b) * (p-side_c))
};Examples
heronArea(3, 4, 5); // 6Returns the number of times num can be divided by divisor (integer or fractional) without getting a fractional answer.
Works for both negative and positive integers.
If divisor is -1 or 1 return Infinity.
If divisor is -0 or 0 return 0.
Otherwise, keep dividing num with divisor and incrementing i, while the result is an integer.
Return the number of times the loop was executed, i.
const howManyTimes = (num, divisor) => {
if (divisor === 1 || divisor === -1) return Infinity;
if (divisor === 0) return 0;
let i = 0;
while (Number.isInteger(num / divisor)) {
i++;
num = num / divisor;
}
return i;
};Examples
howManyTimes(100, 2); // 2
howManyTimes(100, 2.5); // 2
howManyTimes(100, 0); // 0
howManyTimes(100, -1); // InfinityMakes a DELETE request to the passed URL.
Use XMLHttpRequest web api to make a delete request to the given url.
Handle the onload event, by running the provided callback function.
Handle the onerror event, by running the provided err function.
Omit the third argument, err to log the request to the console's error stream by default.
const httpDelete = (url, callback, err = console.error) => {
const request = new XMLHttpRequest();
request.open('DELETE', url, true);
request.onload = () => callback(request);
request.onerror = () => err(request);
request.send();
};Examples
httpDelete('https://website.com/users/123', request => {
console.log(request.responseText);
}); // 'Deletes a user from the database'Makes a PUT request to the passed URL.
Use XMLHttpRequest web api to make a put request to the given url.
Set the value of an HTTP request header with setRequestHeader method.
Handle the onload event, by running the provided callback function.
Handle the onerror event, by running the provided err function.
Omit the last argument, err to log the request to the console's error stream by default.
const httpPut = (url, data, callback, err = console.error) => {
const request = new XMLHttpRequest();
request.open("PUT", url, true);
request.setRequestHeader('Content-type','application/json; charset=utf-8');
request.onload = () => callback(request);
request.onerror = () => err(request);
request.send(data);
};Examples
const password = "fooBaz";
const data = JSON.stringify(password);
httpPut('https://website.com/users/123', data, request => {
console.log(request.responseText);
}); // 'Updates a user's password in database'Checks if the given number is an Armstrong number or not.
Convert the given number into an array of digits. Use the exponent operator (**) to get the appropriate power for each digit and sum them up. If the sum is equal to the number itself, return true otherwise false.
const isArmstrongNumber = digits =>
(arr => arr.reduce((a, d) => a + parseInt(d) ** arr.length, 0) == digits)(
(digits + '').split('')
);Examples
isArmstrongNumber(1634); // true
isArmstrongNumber(56); // falseDetermines if the pattern matches with str.
Use String.toLowerCase() to convert both strings to lowercase, then loop through str and determine if it contains all characters of pattern and in the correct order.
Adapted from here.
const isSimilar = (pattern, str) =>
[...str].reduce(
(matchIndex, char) =>
char.toLowerCase() === (pattern[matchIndex] || '').toLowerCase()
? matchIndex + 1
: matchIndex,
0
) === pattern.length;Examples
isSimilar('rt','Rohit'); // true
isSimilar('tr','Rohit'); // falseConvert kilometers/hour to miles/hour.
Multiply the constant of proportionality with the argument.
const kmphToMph = (kmph) => 0.621371192 * kmph;Examples
kmphToMph(10); // 16.09344000614692
kmphToMph(345.4); // 138.24264965280207Calculates the Levenshtein distance between two strings.
Calculates the number of changes (substitutions, deletions or additions) required to convert string1 to string2.
Can also be used to compare two strings as shown in the second example.
const levenshteinDistance = (string1, string2) => {
if (string1.length === 0) return string2.length;
if (string2.length === 0) return string1.length;
let matrix = Array(string2.length + 1)
.fill(0)
.map((x, i) => [i]);
matrix[0] = Array(string1.length + 1)
.fill(0)
.map((x, i) => i);
for (let i = 1; i <= string2.length; i++) {
for (let j = 1; j <= string1.length; j++) {
if (string2[i - 1] === string1[j - 1]) {
matrix[i][j] = matrix[i - 1][j - 1];
} else {
matrix[i][j] = Math.min(
matrix[i - 1][j - 1] + 1,
matrix[i][j - 1] + 1,
matrix[i - 1][j] + 1
);
}
}
}
return matrix[string2.length][string1.length];
};Examples
levenshteinDistance('30-seconds-of-code','30-seconds-of-python-code'); // 7
const compareStrings = (string1,string2) => (100 - levenshteinDistance(string1,string2) / Math.max(string1.length,string2.length));
compareStrings('30-seconds-of-code', '30-seconds-of-python-code'); // 99.72 (%)Convert miles/hour to kilometers/hour.
Multiply the constant of proportionality with the argument.
const mphToKmph = (mph) => 1.6093440006146922 * mph;Examples
mphToKmph(10); // 16.09344000614692
mphToKmph(85.9); // 138.24264965280207Logs a value and returns it.
Use console.log to log the supplied value, combined with the || operator to return it.
const pipeLog = data => console.log(data) || data;Examples
pipeLog(1); // logs `1` and returns `1`QuickSort an Array (ascending sort by default).
Use recursion.
Use Array.prototype.filter and spread operator (...) to create an array that all elements with values less than the pivot come before the pivot, and all elements with values greater than the pivot come after it.
If the parameter desc is truthy, return array sorts in descending order.
const quickSort = ([n, ...nums], desc) =>
isNaN(n)
? []
: [
...quickSort(nums.filter(v => (desc ? v > n : v <= n)), desc),
n,
...quickSort(nums.filter(v => (!desc ? v > n : v <= n)), desc)
];Examples
quickSort([4, 1, 3, 2]); // [1,2,3,4]
quickSort([4, 1, 3, 2], true); // [4,3,2,1]Returns all the vowels in a str replaced by repl.
Use String.prototype.replace() with a regexp to replace all vowels in str.
Omot repl to use a default value of ''.
const removeVowels = (str, repl = '') => str.replace(/[aeiou]/gi, repl);Examples
removeVowels("foobAr"); // "fbr"
removeVowels("foobAr","*"); // "f**b*r"Solves the given mathematical expression in reverse polish notation.
Throws appropriate errors if there are unrecognized symbols or the expression is wrong. The valid operators are :- +,-,*,/,^,** (^&** are the exponential symbols and are same). This snippet does not supports any unary operators.
Use a dictionary, OPERATORS to specify each operator's matching mathematical operation.
Use String.prototype.replace() with a regular expression to replace ^ with **, String.prototype.split() to tokenize the string and Array.prototype.filter() to remove empty tokens.
Use Array.prototype.forEach() to parse each symbol, evaluate it as a numeric value or operator and solve the mathematical expression.
Numeric values are converted to floating point numbers and pushed to a stack, while operators are evaluated using the OPERATORS dictionary and pop elements from the stack to apply operations.
const solveRPN = rpn => {
const OPERATORS = {
'*': (a, b) => a * b,
'+': (a, b) => a + b,
'-': (a, b) => a - b,
'/': (a, b) => a / b,
'**': (a, b) => a ** b
};
const [stack, solve] = [
[],
rpn
.replace(/\^/g, '**')
.split(/\s+/g)
.filter(el => !/\s+/.test(el) && el !== '')
];
solve.forEach(symbol => {
if (!isNaN(parseFloat(symbol)) && isFinite(symbol)) {
stack.push(symbol);
} else if (Object.keys(OPERATORS).includes(symbol)) {
const [a, b] = [stack.pop(), stack.pop()];
stack.push(OPERATORS[symbol](parseFloat(b), parseFloat(a)));
} else {
throw `${symbol} is not a recognized symbol`;
}
});
if (stack.length === 1) return stack.pop();
else throw `${rpn} is not a proper RPN. Please check it and try again`;
};Examples
solveRPN('15 7 1 1 + - / 3 * 2 1 1 + + -'); // 5
solveRPN('2 3 ^'); // 8Performs speech synthesis (experimental).
Use SpeechSynthesisUtterance.voice and window.speechSynthesis.getVoices() to convert a message to speech.
Use window.speechSynthesis.speak() to play the message.
Learn more about the SpeechSynthesisUtterance interface of the Web Speech API.
const speechSynthesis = message => {
const msg = new SpeechSynthesisUtterance(message);
msg.voice = window.speechSynthesis.getVoices()[0];
window.speechSynthesis.speak(msg);
};Examples
speechSynthesis('Hello, World'); // // plays the messageSquares each number in an array and then sums the results together.
Use Array.prototype.reduce() in combination with Math.pow() to iterate over numbers and sum their squares into an accumulator.
const squareSum = (...args) => args.reduce((squareSum, number) => squareSum + Math.pow(number, 2), 0);Examples
squareSum(1, 2, 2); // 9