30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
30 seconds of codeCurated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
309
snippets
118
contributors
3309
commits
20692
stars
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.
In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
Creates an element from a string (without appending it to the document). If the given string contains multiple elements, only the first one will be returned.
Use document.createElement() to create a new element. Set its innerHTML to the string supplied as the argument. Use ParentNode.firstElementChild to return the element version of the string.
const createElement = str => { - const el = document.createElement('div'); - el.innerHTML = str; - return el.firstElementChild; -}; -
const el = createElement( - `<div class="container"> - <p>Hello!</p> - </div>` -); -console.log(el.className); // 'container' -
Moves the specified amount of elements to the end of the array.
Use Array.slice() twice to get the elements after the specified index and the elements before that. Use the spread operator(...) to combine the two into one array. If offset is negative, the elements will be moved from end to start.
const offset = (arr, offset) => [...arr.slice(offset), ...arr.slice(0, offset)]; -
offset([1, 2, 3, 4, 5], 2); // [3, 4, 5, 1, 2] -offset([1, 2, 3, 4, 5], -2); // [4, 5, 1, 2, 3] -
Returns all unique values of an array.
Use ES6 Set and the ...rest operator to discard all duplicated values.
const uniqueElements = arr => [...new Set(arr)]; -
uniqueElements([1, 2, 2, 3, 4, 4, 5]); // [1,2,3,4,5] +30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.309
snippets118
contributors3311
commits20705
starsOur philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.
In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.
Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
flatten
Flattens an array up to the specified depth.
Use recursion, decrementing
depthby 1 for each level of depth. UseArray.reduce()andArray.concat()to merge elements or arrays. Base case, fordepthequal to1stops recursion. Omit the second argument,depthto flatten only to a depth of1(single flatten).const flatten = (arr, depth = 1) => + arr.reduce((a, v) => a.concat(depth > 1 && Array.isArray(v) ? flatten(v, depth - 1) : v), []); +flatten([1, [2], 3, 4]); // [1, 2, 3, 4] +flatten([1, [2, [3, [4, 5], 6], 7], 8], 2); // [1, 2, 3, [4, 5], 6, 7, 8] +isPromiseLike
Returns
trueif an object looks like aPromise,falseotherwise.Check if the object is not
null, itstypeofmatches eitherobjectorfunctionand if it has a.thenproperty, which is also afunction.const isPromiseLike = obj => + obj !== null && + (typeof obj === 'object' || typeof obj === 'function') && + typeof obj.then === 'function'; +isPromiseLike({ + then: function() { + return ''; + } +}); // true +isPromiseLike(null); // false +isPromiseLike({}); // false +unzipWith
Creates an array of elements, ungrouping the elements in an array produced by zip and applying the provided function.
Use
Math.max.apply()to get the longest subarray in the array,Array.map()to make each element an array. UseArray.reduce()andArray.forEach()to map grouped values to individual arrays. UseArray.map()and the spread operator (...) to applyfnto each individual group of elements.const unzipWith = (arr, fn) => + arr + .reduce( + (acc, val) => (val.forEach((v, i) => acc[i].push(v)), acc), + Array.from({ + length: Math.max(...arr.map(x => x.length)) + }).map(x => []) + ) + .map(val => fn(...val)); +unzipWith([[1, 10, 100], [2, 20, 200]], (...args) => args.reduce((acc, v) => acc + v, 0)); // [3, 30, 300]Getting started
- If you are new to JavaScript, we suggest you start by taking a look at the Beginner's snippets
- If you want to level up your JavaScript skills, check out the full Snippet collection
- If you want to see how the project was built and contribute, visit our Github repository
- If you want to check out some more complex snippets, you can visit the Archive
Related projects
The idea behind 30 seconds of code has inspired some people to create similar collections in other programming languages and environments. Here are the ones we like the most:
- 30 seconds of CSS by atomiks
- 30 seconds of Interviews by fejes713
- 30 seconds of Python by kriadmin
How to contribute
Do you have a cool idea for a new snippet? Maybe some code you use often and is not part of our collection? Contributing to 30 seconds of code is as simple as 1,2,3,4!
1Create
Start by creating a snippet, according to the snippet template. Make sure to follow these simple guidelines:
- Your snippet title must be unique and the same as the name of the implemented function.
- Use the snippet description to explain what your snippet does and how it works.
- Try to keep the snippet's code short and to the point. Use modern techniques and features.
- Remember to provide an example of how your snippet works.
- Your snippet should solve a real-world problem, no matter how simple.
- Never modify README.md or any of the HTML files.
2Tag
Run
npm run taggerfrom your terminal, then open the tag_database file and tag your snippet appropriately. Multitagging is also supported, just make sure the first tag you specify is on of the major tags and the one that is most relevant to the implemneted function.3Test
You can optionally test your snippet to make our job easier. Simply run
npm run testerto generate the test files for your snippet. Find the related folder for you snippet under the test directory and write some tests. Remember to runnpm run testeragain to make sure your tests are passing.4Pull request
If you have done everything mentioned above, you should now have an awesome snippet to add to our collection. Simply start a pull request and follow the guidelines provided. Remember to only submit one snippet per pull request, so that we can quickly evaluate and merge your code into the collection.
If you need additional pointers about writing a snippet, be sure to read the complete contribution guidelines.
