Curated collection of useful Javascript snippets that you can understand in 30 seconds or less.
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- Snippets are written in ES6, use the Babel transpiler to ensure backwards-compatibility.
- Array difference
- Array intersection
- Array remove
- Array sample
- Array symmetric difference
- Array union
- Array without
- Array zip
- Average of array of numbers
- Chunk array
- Compact
- Count occurrences of a value in array
- Deep flatten array
- Drop elements in array
- Fill array
- Filter out non unique values in an array
- Flatten array up to depth
- Flatten array
- Get max value from array
- Get min value from array
- Group by
- Head of list
- Initial of list
- Initialize array with range
- Initialize array with values
- Last of list
- Median of array of numbers
- Nth element of array
- Pick
- Shuffle array
- Similarity between arrays
- Sum of array of numbers
- Tail of list
- Take every nth element
- Take right
- Take
- Unique values of array
- Bottom visible
- Current URL
- Element is visible in viewport
- Get scroll position
- Redirect to URL
- Scroll to top
- Chain asynchronous functions
- Compose functions
- Curry
- Log function name
- Pipe functions
- Promisify
- Run promises in series
- Sleep
- Collatz algorithm
- Distance between two points
- Divisible by number
- Even or odd number
- Factorial
- Fibonacci array generator
- Greatest common divisor (GCD)
- Hamming distance
- Percentile
- Powerset
- Random integer in range
- Random number in range
- Round number to n digits
- Standard deviation
- Anagrams of string (with duplicates)
- Capitalize first letter of every word
- Capitalize first letter
- Check for palindrome
- Convert string from camelcase
- Convert string to camelcase
- Reverse a string
- Sort characters in string (alphabetical)
- Truncate a string
- 3 digit hexcode to 6 digit hexcode
- Escape regular expression
- Get native type of value
- Hexcode to RGB
- Is array
- Is boolean
- Is function
- Is number
- Is string
- Is symbol
- Measure time taken by function
- Number to array of digits
- Ordinal suffix of number
- RGB to hexadecimal
- URL parameters
- UUID generator
- Validate email
- Validate number
Create a Set from b, then use Array.filter() on a to only keep values not contained in b.
const difference = (a, b) => { const s = new Set(b); return a.filter(x => !s.has(x)); };
// difference([1,2,3], [1,2,4]) -> [3]Create a Set from b, then use Array.filter() on a to only keep values contained in b.
const intersection = (a, b) => { const s = new Set(b); return a.filter(x => s.has(x)); };
// intersection([1,2,3], [4,3,2]) -> [2,3]Use Array.filter() to find array elements that return truthy values and Array.reduce() to remove elements using Array.splice().
The func is invoked with three arguments (value, index, array).
const remove = (arr, func) =>
Array.isArray(arr) ? arr.filter(func).reduce((acc, val) => {
arr.splice(arr.indexOf(val), 1); return acc.concat(val);
}, [])
: [];
// remove([1, 2, 3, 4], n => n % 2 == 0) -> [2, 4]Use Math.random() to generate a random number, multiply it with length and round it of to the nearest whole number using Math.floor().
This method also works with strings.
const sample = arr => arr[Math.floor(Math.random() * arr.length)];
// sample([3, 7, 9, 11]) -> 9Create a Set from each array, then use Array.filter() on each of them to only keep values not contained in the other.
const symmetricDifference = (a, b) => {
const sA = new Set(a), sB = new Set(b);
return [...a.filter(x => !sB.has(x)), ...b.filter(x => !sA.has(x))];
}
// symmetricDifference([1,2,3], [1,2,4]) -> [3,4]Create a Set with all values of a and b and convert to an array.
const union = (a, b) => Array.from(new Set([...a, ...b]));
// union([1,2,3], [4,3,2]) -> [1,2,3,4]Use Array.filter() to create an array excluding(using !Array.includes()) all given values.
const without = (arr, ...args) => arr.filter(v => !args.includes(v));
// without([2, 1, 2, 3], 1, 2) -> [3]
// without([2, 1, 2, 3, 4, 5, 5, 5, 3, 2, 7, 7], 3, 1, 5, 2) -> [ 4, 7, 7 ]Use Math.max.apply() to get the longest array in the arguments.
Creates an array with that length as return value and use Array.from() with a map-function to create an array of grouped elements.
If lengths of the argument-arrays vary, undefined is used where no value could be found.
const zip = (...arrays) => {
const maxLength = Math.max(...arrays.map(x => x.length));
return Array.from({length: maxLength}).map((_, i) => {
return Array.from({length: arrays.length}, (_, k) => arrays[k][i]);
})
}
//zip(['a', 'b'], [1, 2], [true, false]); -> [['a', 1, true], ['b', 2, false]]
//zip(['a'], [1, 2], [true, false]); -> [['a', 1, true], [undefined, 2, false]]Use Array.reduce() to add each value to an accumulator, initialized with a value of 0, divide by the length of the array.
const average = arr => arr.reduce((acc, val) => acc + val, 0) / arr.length;
// average([1,2,3]) -> 2Use Array.from() to create a new array, that fits the number of chunks that will be produced.
Use Array.slice() to map each element of the new array to a chunk the length of size.
If the original array can't be split evenly, the final chunk will contain the remaining elements.
const chunk = (arr, size) =>
Array.from({length: Math.ceil(arr.length / size)}, (v, i) => arr.slice(i * size, i * size + size));
// chunk([1,2,3,4,5], 2) -> [[1,2],[3,4],[5]]Use Array.filter() to filter out falsey values (false, null, 0, "", undefined, and NaN).
const compact = (arr) => arr.filter(v => v);
// compact([0, 1, false, 2, '', 3, 'a', 'e'*23, NaN, 's', 34]) -> [ 1, 2, 3, 'a', 's', 34 ]Use Array.reduce() to increment a counter each time you encounter the specific value inside the array.
const countOccurrences = (arr, value) => arr.reduce((a, v) => v === value ? a + 1 : a + 0, 0);
// countOccurrences([1,1,2,1,2,3], 1) -> 3Use recursion.
Use Array.concat() with an empty array ([]) and the spread operator (...) to flatten an array.
Recursively flatten each element that is an array.
const deepFlatten = arr => [].concat(...arr.map(v => Array.isArray(v) ? deepFlatten(v) : v));
// deepFlatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]Loop through the array, using Array.shift() to drop the first element of the array until the returned value from the function is true.
Returns the remaining elements.
const dropElements = (arr, func) => {
while (arr.length > 0 && !func(arr[0])) arr.shift();
return arr;
};
// dropElements([1, 2, 3, 4], n => n >= 3) -> [3,4]Use Array.map() to map values between start (inclusive) and end (exclusive) to value.
Omit start to start at the first element and/or end to finish at the last.
const fillArray = (arr, value, start = 0, end = arr.length) =>
arr.map((v, i) => i >= start && i < end ? value : v);
// fillArray([1,2,3,4],'8',1,3) -> [1,'8','8',4]Use Array.filter() for an array containing only the unique values.
const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
// filterNonUnique([1,2,2,3,4,4,5]) -> [1,3,5]Use recursion, decrementing depth by 1 for each level of depth.
Use Array.reduce() and Array.concat() to merge elements or arrays.
Base case, for depth equal to 1 stops recursion.
Omit the second element, depth to flatten only to a depth of 1 (single flatten).
const flattenDepth = (arr, depth = 1) =>
depth != 1 ? arr.reduce((a, v) => a.concat(Array.isArray(v) ? flattenDepth(v, depth - 1) : v), [])
: arr.reduce((a, v) => a.concat(v), []);
// flattenDepth([1,[2],[[[3],4],5]], 2) -> [1,2,[3],4,5]Use Array.reduce() to get all elements inside the array and concat() to flatten them.
const flatten = arr => arr.reduce((a, v) => a.concat(v), []);
// flatten([1,[2],3,4]) -> [1,2,3,4]Use Math.max() combined with the spread operator (...) to get the maximum value in the array.
const arrayMax = arr => Math.max(...arr);
// arrayMax([10, 1, 5]) -> 10Use Math.min() combined with the spread operator (...) to get the minimum value in the array.
const arrayMin = arr => Math.min(...arr);
// arrayMin([10, 1, 5]) -> 1Use Array.map() to map the values of an array to a function or property name.
Use Array.reduce() to create an object, where the keys are produced from the mapped results.
const groupBy = (arr, func) =>
arr.map(typeof func === 'function' ? func : val => val[func])
.reduce((acc, val, i) => { acc[val] = (acc[val] || []).concat(arr[i]); return acc; }, {});
// groupBy([6.1, 4.2, 6.3], Math.floor) -> {4: [4.2], 6: [6.1, 6.3]}
// groupBy(['one', 'two', 'three'], 'length') -> {3: ['one', 'two'], 5: ['three']}Use arr[0] to return the first element of the passed array.
const head = arr => arr[0];
// head([1,2,3]) -> 1Use arr.slice(0,-1)to return all but the last element of the array.
const initial = arr => arr.slice(0, -1);
// initial([1,2,3]) -> [1,2]Use Array(end-start) to create an array of the desired length, Array.map() to fill with the desired values in a range.
You can omit start to use a default value of 0.
const initializeArrayRange = (end, start = 0) =>
Array.from({ length: end - start }).map((v, i) => i + start);
// initializeArrayRange(5) -> [0,1,2,3,4]Use Array(n) to create an array of the desired length, fill(v) to fill it with the desired values.
You can omit value to use a default value of 0.
const initializeArray = (n, value = 0) => Array(n).fill(value);
// initializeArray(5, 2) -> [2,2,2,2,2]Use arr.slice(-1)[0] to get the last element of the given array.
const last = arr => arr.slice(-1)[0];
// last([1,2,3]) -> 3Find the middle of the array, use Array.sort() to sort the values.
Return the number at the midpoint if length is odd, otherwise the average of the two middle numbers.
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;
};
// median([5,6,50,1,-5]) -> 5
// median([0,10,-2,7]) -> 3.5Use Array.slice() to get an array containing the nth element at the first place.
If the index is out of bounds, return [].
Omit the second argument, n, to get the first element of the array.
const nth = (arr, n=0) => (n>0? arr.slice(n,n+1) : arr.slice(n))[0];
// nth(['a','b','c'],1) -> 'b'
// nth(['a','b','b']-2) -> 'a'Use Array.reduce() to convert the filtered/picked keys back to a object with the corresponding key:value pair if the key exist in the obj.
const pick = (obj, arr) =>
arr.reduce((acc, curr) => (curr in obj && (acc[curr] = obj[curr]), acc), {});
// pick({ 'a': 1, 'b': '2', 'c': 3 }, ['a', 'c']) -> { 'a': 1, 'c': 3 }
// pick(object, ['a', 'c'])['a'] -> 1Use Array.sort() to reorder elements, using Math.random() in the comparator.
const shuffle = arr => arr.sort(() => Math.random() - 0.5);
// shuffle([1,2,3]) -> [2,3,1]Use filter() to remove values that are not part of values, determined using includes().
const similarity = (arr, values) => arr.filter(v => values.includes(v));
// similarity([1,2,3], [1,2,4]) -> [1,2]Use Array.reduce() to add each value to an accumulator, initialized with a value of 0.
const sum = arr => arr.reduce((acc, val) => acc + val, 0);
// sum([1,2,3,4]) -> 10Return arr.slice(1) if the array's length is more than 1, otherwise return the whole array.
const tail = arr => arr.length > 1 ? arr.slice(1) : arr;
// tail([1,2,3]) -> [2,3]
// tail([1]) -> [1]Use Array.filter() to create a new array that contains every nth element of a given array.
const everynth = (arr, nth) => arr.filter((e, i) => i % nth === 0);
// everynth([1,2,3,4,5,6], 2) -> [ 1, 3, 5 ]Use Array.slice() to create a slice of the array with n elements taken from the end.
const takeRight = (arr, n = 1) => arr.slice(arr.length - n, arr.length);
// takeRight([1, 2, 3], 2) -> [ 2, 3 ]
// takeRight([1, 2, 3]) -> [3]Use Array.slice() to create a slice of the array with n elements taken from the beginning.
const take = (arr, n = 1) => arr.slice(0, n);
// take([1, 2, 3], 5) -> [1, 2, 3]
// take([1, 2, 3], 0) -> []Use ES6 Set and the ...rest operator to discard all duplicated values.
const unique = arr => [...new Set(arr)];
// unique([1,2,2,3,4,4,5]) -> [1,2,3,4,5]Use scrollY, scrollHeight and clientHeight to determine if the bottom of the page is visible.
const bottomVisible = _ =>
document.documentElement.clientHeight + window.scrollY >= document.documentElement.scrollHeight || document.documentElement.clientHeight;
// bottomVisible() -> trueUse window.location.href to get current URL.
const currentUrl = _ => window.location.href;
// currentUrl() -> 'https://google.com'Use Element.getBoundingClientRect() and the window.inner(Width|Height) values
to determine if a given element is visible in the viewport.
Omit the second argument to determine if the element is entirely visible, or specify true to determine if
it is partially visible.
const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
const { top, left, bottom, right } = el.getBoundingClientRect();
return partiallyVisible
? ((top > 0 && top < innerHeight) || (bottom > 0 && bottom < innerHeight)) &&
((left > 0 && left < innerWidth) || (right > 0 && right < innerWidth))
: top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth;
};
// e.g. 100x100 viewport and a 10x10px element at position {top: -1, left: 0, bottom: 9, right: 10}
// elementIsVisibleInViewport(el) -> false (not fully visible)
// elementIsVisibleInViewport(el, true) -> true (partially visible)Use pageXOffset and pageYOffset if they are defined, otherwise scrollLeft and scrollTop.
You can omit el to use a default value of window.
const getScrollPos = (el = window) =>
({x: (el.pageXOffset !== undefined) ? el.pageXOffset : el.scrollLeft,
y: (el.pageYOffset !== undefined) ? el.pageYOffset : el.scrollTop});
// getScrollPos() -> {x: 0, y: 200}Use window.location.href or window.location.replace() to redirect to url.
Pass a second argument to simulate a link click (true - default) or an HTTP redirect (false).
const redirect = (url, asLink = true) =>
asLink ? window.location.href = url : window.location.replace(url);
// redirect('https://google.com')Get distance from top using document.documentElement.scrollTop or document.body.scrollTop.
Scroll by a fraction of the distance from top. Use window.requestAnimationFrame() to animate the scrolling.
const scrollToTop = _ => {
const c = document.documentElement.scrollTop || document.body.scrollTop;
if (c > 0) {
window.requestAnimationFrame(scrollToTop);
window.scrollTo(0, c - c / 8);
}
};
// scrollToTop()Calculate the difference (in days) between to Date objects.
const getDaysDiffBetweenDates = (dateInitial, dateFinal) => (dateFinal - dateInitial) / (1000 * 3600 * 24);
// getDaysDiffBetweenDates(new Date("2017-12-13"), new Date("2017-12-22")) -> 9Use 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() }`
};
// jsonToDate(/Date(1489525200000)/) -> "14/3/2017"Loop through an array of functions containing asynchronous events, calling next when each asynchronous event has completed.
const chainAsync = fns => { let curr = 0; const next = () => fns[curr++](next); next(); };
/*
chainAsync([
next => { console.log('0 seconds'); setTimeout(next, 1000); },
next => { console.log('1 second'); setTimeout(next, 1000); },
next => { console.log('2 seconds'); }
])
*/Use Array.reduce() to perform right-to-left function composition.
The last (rightmost) function can accept one or more arguments; the remaining functions must be unary.
const compose = (...fns) => fns.reduce((f, g) => (...args) => f(g(...args)));
/*
const add5 = x => x + 5
const multiply = (x, y) => x * y
const multiplyAndAdd5 = compose(add5, multiply)
multiplyAndAdd5(5, 2) -> 15
*/Use recursion.
If the number of provided arguments (args) is sufficient, call the passed function f.
Otherwise return a curried function f that expects the rest of the arguments.
If you want to curry a function that accepts a variable number of arguments (a variadic function, e.g. Math.min()), you can optionally pass the number of arguments to the second parameter arity.
const curry = (fn, arity = fn.length, ...args) =>
arity <= args.length
? fn(...args)
: curry.bind(null, fn, arity, ...args);
// curry(Math.pow)(2)(10) -> 1024
// curry(Math.min, 3)(10)(50)(2) -> 2Use console.debug() and the name property of the passed method to log the method's name to the debug channel of the console.
const functionName = fn => (console.debug(fn.name), fn);
// functionName(Math.max) -> max (logged in debug channel of console)Use Array.reduce() with the spread operator (...) to perform left-to-right function composition.
The first (leftmost) function can accept one or more arguments; the remaining functions must be unary.
const pipe = (...fns) => fns.reduce((f, g) => (...args) => g(f(...args)));
/*
const add5 = x => x + 5
const multiply = (x, y) => x * y
const multiplyAndAdd5 = pipe(multiply, add5)
multiplyAndAdd5(5, 2) -> 15
*/Use currying to return a function returning a Promise that calls the original function.
Use the ...rest operator to pass in all the parameters.
In Node 8+, you can use util.promisify
const promisify = func =>
(...args) =>
new Promise((resolve, reject) =>
func(...args, (err, result) =>
err ? reject(err) : resolve(result))
);
// const delay = promisify((d, cb) => setTimeout(cb, d))
// delay(2000).then(() => console.log('Hi!')) -> Promise resolves after 2sRun an array of promises in series using Array.reduce() by creating a promise chain, where each promise returns the next promise when resolved.
const series = ps => ps.reduce((p, next) => p.then(next), Promise.resolve());
// const delay = (d) => new Promise(r => setTimeout(r, d))
// series([() => delay(1000), () => delay(2000)]) -> executes each promise sequentially, taking a total of 3 seconds to completeDelay executing part of an async function, by putting it to sleep, returning a Promise.
const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));
/*
async function sleepyWork() {
console.log('I\'m going to sleep for 1 second.');
await sleep(1000);
console.log('I woke up after 1 second.');
}
*/If n is even, return n/2. Otherwise return 3n+1.
const collatz = n => (n % 2 == 0) ? (n / 2) : (3 * n + 1);
// collatz(8) --> 4
// collatz(5) --> 16Use Math.hypot() to calculate the Euclidean distance between two points.
const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);
// distance(1,1, 2,3) -> 2.23606797749979Use the modulo operator (%) to check if the remainder is equal to 0.
const isDivisible = (dividend, divisor) => dividend % divisor === 0;
// isDivisible(6,3) -> trueChecks whether a number is odd or even using the modulo (%) operator.
Returns true if the number is even, false if the number is odd.
const isEven = num => num % 2 === 0;
// isEven(3) -> falseUse recursion.
If n is less than or equal to 1, return 1.
Otherwise, return the product of n and the factorial of n - 1.
Throws an exception if n is a negative number.
const factorial = n =>
n < 0 ? (() => { throw new TypeError('Negative numbers are not allowed!') })()
: n <= 1 ? 1 : n * factorial(n - 1);
// factorial(6) -> 720Create an empty array of the specific length, initializing the first two values (0 and 1).
Use Array.reduce() to add values into the array, using the sum of the last two values, except for the first two.
const fibonacci = n =>
Array(n).fill(0).reduce((acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i), []);
// fibonacci(5) -> [0,1,1,2,3]Use recursion.
Base case is when y equals 0. In this case, return x.
Otherwise, return the GCD of y and the remainder of the division x/y.
const gcd = (x, y) => !y ? x : gcd(y, x % y);
// gcd (8, 36) -> 4Use XOR operator (^) to find the bit difference between the two numbers, convert to binary string using toString(2).
Count and return the number of 1s in the string, using match(/1/g).
const hammingDistance = (num1, num2) =>
((num1 ^ num2).toString(2).match(/1/g) || '').length;
// hammingDistance(2,3) -> 1Use Array.reduce() to calculate how many numbers are below the value and how many are the same value and
apply the percentile formula.
const percentile = (arr, val) =>
100 * arr.reduce((acc,v) => acc + (v < val ? 1 : 0) + (v === val ? 0.5 : 0), 0) / arr.length;
// percentile([1,2,3,4,5,6,7,8,9,10], 6) -> 55Use Array.reduce() combined with Array.map() to iterate over elements and combine into an array containing all combinations.
const powerset = arr =>
arr.reduce((a, v) => a.concat(a.map(r => [v].concat(r))), [[]]);
// powerset([1,2]) -> [[], [1], [2], [2,1]]Use Math.random() to generate a random number and map it to the desired range, using Math.floor() to make it an integer.
const randomIntegerInRange = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;
// randomIntegerInRange(0, 5) -> 2Use Math.random() to generate a random value, map it to the desired range using multiplication.
const randomInRange = (min, max) => Math.random() * (max - min) + min;
// randomInRange(2,10) -> 6.0211363285087005Use Math.round() and template literals to round the number to the specified number of digits.
Omit the second argument, decimals to round to an integer.
const round = (n, decimals=0) => Number(`${Math.round(`${n}e${decimals}`)}e-${decimals}`);
// round(1.005, 2) -> 1.01Use Array.reduce() to calculate the mean, variance and the sum of the variance of the values, the variance of the values, then
determine the standard deviation.
You can omit the second argument to get the sample standard deviation or set it to true to get the population standard deviation.
const standardDeviation = (arr, usePopulation = false) => {
const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
return Math.sqrt(
arr.reduce((acc, val) => acc.concat(Math.pow(val - mean, 2)), [])
.reduce((acc, val) => acc + val, 0) / (arr.length - (usePopulation ? 0 : 1))
);
};
// standardDeviation([10,2,38,23,38,23,21]) -> 13.284434142114991 (sample)
// standardDeviation([10,2,38,23,38,23,21], true) -> 12.29899614287479 (population)Use SpeechSynthesisUtterance.voice and indow.speechSynthesis.getVoices() to convert a message to speech.
Use window.speechSynthesis.speak() to play the message.
Learn more about the SpeechSynthesisUtterance interface of the Web Speech API.
const speak = message => {
const msg = new SpeechSynthesisUtterance(message);
msg.voice = window.speechSynthesis.getVoices()[0];
window.speechSynthesis.speak(msg);
};
// speak('Hello, World') -> plays the messageUse readFileSync function in fs node package to create a Buffer from a file.
convert buffer to string using toString(encoding) function.
creating an array from contents of file by spliting file content line by line(each \n).
const fs = require('fs');
const readFileToArray = filename => fs.readFileSync(filename).toString('UTF8').split('\n');
/*
contents of test.txt :
line1
line2
line3
___________________________
let arr = readFileToArray('test.txt')
console.log(arr) // -> ['line1', 'line2', 'line3']
*/Use fs.writeFile(), template literals and JSON.stringify() to write a json object to a .json file.
const fs = require('fs');
const jsonToFile = (obj, filename) => fs.writeFile(`${filename}.json`, JSON.stringify(obj, null, 2))
// jsonToFile({test: "is passed"}, 'testJsonFile') -> writes the object to 'testJsonFile.json'Use Object.keys() method to loop over given json object and deleting keys that are not included in given array.
also if you give it a special key(childIndicator) it will search deeply inside it to apply 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];
}
})
}
/*
testObj = {a: 1, b: 2, children: {a: 1, b: 2}}
cleanObj(testObj, ["a"],"children")
console.log(testObj)// { a: 1, children : { a: 1}}
*/Use Array.reduce() to create and combine key-value pairs.
const objectFromPairs = arr => arr.reduce((a, v) => (a[v[0]] = v[1], a), {});
// objectFromPairs([['a',1],['b',2]]) -> {a: 1, b: 2}Use Object.keys() and Array.map() to iterate over the object's keys and produce an array with key-value pairs.
const objectToPairs = obj => Object.keys(obj).map(k => [k, obj[k]]);
// objectToPairs({a: 1, b: 2}) -> [['a',1],['b',2]])Use Object.assign() and an empty object ({}) to create a shallow clone of the original.
const shallowClone = obj => Object.assign({}, obj);
/*
const a = { x: true, y: 1 };
const b = shallowClone(a);
a === b -> false
*/Use recursion.
For each letter in the given string, create all the partial anagrams for the rest of its letters.
Use Array.map() to combine the letter with each partial anagram, then Array.reduce() to combine all anagrams in one array.
Base cases are for string length equal to 2 or 1.
const anagrams = str => {
if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str];
return str.split('').reduce((acc, letter, i) =>
acc.concat(anagrams(str.slice(0, i) + str.slice(i + 1)).map(val => letter + val)), []);
};
// anagrams('abc') -> ['abc','acb','bac','bca','cab','cba']Use replace() to match the first character of each word and toUpperCase() to capitalize it.
const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());
// capitalizeEveryWord('hello world!') -> 'Hello World!'Use destructuring and toUpperCase() to capitalize first letter, ...rest to get array of characters after first letter and then Array.join('') to make it a string again.
Omit the lowerRest parameter to keep the rest of the string intact, or set it to true to convert to lower case.
const capitalize = ([first,...rest], lowerRest = false) =>
first.toUpperCase() + (lowerRest ? rest.join('').toLowerCase() : rest.join(''));
// capitalize('myName') -> 'MyName'
// capitalize('myName', true) -> 'Myname'Convert string toLowerCase() and use replace() to remove non-alphanumeric characters from it.
Then, split('') into individual characters, reverse(), join('') and compare to the original, unreversed string, after converting it tolowerCase().
const palindrome = str => {
const s = str.toLowerCase().replace(/[\W_]/g,'');
return s === s.split('').reverse().join('');
}
// palindrome('taco cat') -> trueUse replace() to remove underscores, hyphens and spaces and convert words to camelcase.
Omit the scond argument to use a default separator of '_'.
const fromCamelCase = (str, separator = '_') =>
str.replace(/([a-z\d])([A-Z])/g, '$1' + separator + '$2')
.replace(/([A-Z]+)([A-Z][a-z\d]+)/g, '$1' + separator + '$2').toLowerCase();
// decamelize('someDatabaseFieldName', ' ') -> 'some database field name'
// decamelize('someLabelThatNeedsToBeCamelized', '-') -> 'some-label-that-needs-to-be-camelized'
// decamelize('someJavascriptProperty', '_') -> 'some_javascript_property'Use replace() to remove underscores, hyphens and spaces and convert words to camelcase.
const toCamelCase = str =>
str.replace(/^([A-Z])|[\s-_]+(\w)/g, (match, p1, p2, offset) => p2 ? p2.toUpperCase() : p1.toLowerCase());
// camelize("some_database_field_name") -> 'someDatabaseFieldName'
// camelize("Some label that needs to be camelized") -> 'someLabelThatNeedsToBeCamelized'
// camelize("some-javascript-property") -> 'someJavascriptProperty'
// camelize("some-mixed_string with spaces_underscores-and-hyphens") -> 'someMixedStringWithSpacesUnderscoresAndHyphens'Use array destructuring and Array.reverse() to reverse the order of the characters in the string.
Combine characters to get a string using join('').
const reverseString = str => [...str].reverse().join('');
// reverseString('foobar') -> 'raboof'Split the string using split(''), Array.sort() utilizing localeCompare(), recombine using join('').
const sortCharactersInString = str =>
str.split('').sort((a, b) => a.localeCompare(b)).join('');
// sortCharactersInString('cabbage') -> 'aabbceg'Determine if the string's length is greater than num.
Return the string truncated to the desired length, with ... appended to the end or the original string.
const truncate = (str, num) =>
str.length > num ? str.slice(0, num > 3 ? num - 3 : num) + '...' : str;
// truncate('boomerang', 7) -> 'boom...'Use Array.map(), split() and Array.join() to join the mapped array for converting a three-digit RGB notated hexadecimal colorcode to the six-digit form.
const convertHex = shortHex =>
shortHex[0] == '#' ? ('#' + shortHex.slice(1).split('').map(x => x+x).join('')) :
('#' + shortHex.split('').map(x => x+x).join(''));
// convertHex('#03f') -> '#0033ff'
// convertHex('05a') -> '#0055aa'Use replace() to escape special characters.
const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
// escapeRegExp('(test)') -> \\(test\\)Returns lower-cased constructor name of value, "undefined" or "null" if value is undefined or null
const getType = v =>
v === undefined ? 'undefined' : v === null ? 'null' : v.constructor.name.toLowerCase();
// getType(new Set([1,2,3])) -> "set"Use Array.slice(), Array.map() and match() to convert a hexadecimal colorcode (prefixed with #) to a string with the RGB values.
const hexToRgb = hex => `rgb(${hex.slice(1).match(/.{2}/g).map(x => parseInt(x, 16)).join()})`
// hexToRgb('#27ae60') -> 'rgb(39,174,96)'Use Array.isArray() to check if a value is classified as an array.
const isArray = val => !!val && Array.isArray(val);
// isArray(null) -> false
// isArray([1]) -> trueUse typeof to check if a value is classified as a boolean primitive.
const isBoolean = val => typeof val === 'boolean';
// isBoolean(null) -> false
// isBoolean(false) -> trueUse typeof to check if a value is classified as a function primitive.
const isFunction = val => val && typeof val === 'function';
// isFunction('x') -> false
// isFunction(x => x) -> trueUse typeof to check if a value is classified as a number primitive.
const isNumber = val => typeof val === 'number';
// isNumber('1') -> false
// isNumber(1) -> trueUse typeof to check if a value is classified as a string primitive.
const isString = val => typeof val === 'string';
// isString(10) -> false
// isString('10') -> trueUse typeof to check if a value is classified as a symbol primitive.
const isSymbol = val => typeof val === 'symbol';
// isSymbol('x') -> false
// isSymbol(Symbol('x')) -> trueUse console.time() and console.timeEnd() to measure the difference between the start and end times to determine how long the callback took to execute.
const timeTaken = callback => {
console.time('timeTaken');
const r = callback();
console.timeEnd('timeTaken');
return r;
};
// timeTaken(() => Math.pow(2, 10)) -> 1024
// (logged): timeTaken: 0.02099609375msConvert the number to a string, use split() to convert build an array.
Use Array.map() and parseInt() to transform each value to an integer.
const digitize = n => (''+n).split('').map(i => parseInt(i));
// digitize(2334) -> [2, 3, 3, 4]Use the modulo operator (%) to find values of single and tens digits.
Find which ordinal pattern digits match.
If digit is found in teens pattern, use teens ordinal.
const toOrdinalSuffix = num => {
const int = parseInt(num), digits = [(int % 10), (int % 100)],
ordinals = ['st', 'nd', 'rd', 'th'], oPattern = [1, 2, 3, 4],
tPattern = [11, 12, 13, 14, 15, 16, 17, 18, 19];
return oPattern.includes(digits[0]) && !tPattern.includes(digits[1]) ? int + ordinals[digits[0] - 1] : int + ordinals[3];
};
// toOrdinalSuffix("123") -> "123rd"Convert given RGB parameters to hexadecimal string using bitwise left-shift operator (<<) and toString(16), then padStart(6,'0') to get a 6-digit hexadecimal value.
const rgbToHex = (r, g, b) => ((r << 16) + (g << 8) + b).toString(16).padStart(6, '0');
// rgbToHex(255, 165, 1) -> 'ffa501'Use match() with an appropriate regular expression to get all key-value pairs, Array.reduce() to map and combine them into a single object.
Pass location.search as the argument to apply to the current url.
const getUrlParameters = url =>
url.match(/([^?=&]+)(=([^&]*))/g).reduce(
(a, v) => (a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1), a), {}
);
// getUrlParameters('http://url.com/page?name=Adam&surname=Smith') -> {name: 'Adam', surname: 'Smith'}Use crypto API to generate a UUID, compliant with RFC4122 version 4.
const uuid = _ =>
([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c =>
(c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
);
// uuid() -> '7982fcfe-5721-4632-bede-6000885be57d'Use a regular expression to check if the email is valid.
Returns true if email is valid, false if not.
const validateEmail = str =>
/^(([^<>()\[\]\\.,;:\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,}))$/.test(str);
// validateEmail([email protected]) -> trueUse !isNaN in combination with parseFloat() to check if the argument is a number.
Use isFinite() to check if the number is finite.
Use Number() to check if the coercion holds.
const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n) && Number(n) == n;
// validateNumber('10') -> trueIcons made by Smashicons from www.flaticon.com is licensed by CC 3.0 BY.