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.
304
snippets
118
contributors
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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:
Initializes a 2D array of given width and height and value.
Use Array.map() to generate h rows where each is a new array of size w initialize with value. If the value is not provided, default to null.
const initialize2DArray = (w, h, val = null) => Array.from({ length: h }).map(() => Array.from({ length: w }).fill(val));
initialize2DArray(2, 2, 0); // [[0,0], [0,0]]
Returns a list of elements that exist in both arrays.
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]
⚠️ WARNING: This function's execution time increases exponentially with each character. Anything more than 8 to 10 characters will cause your browser to hang as it tries to solve all the different combinations.
Generates all permutations of a string (contains duplicates).
Use recursion. For each letter in the given string, create all the partial permutations for the rest of its letters. Use Array.map() to combine the letter with each partial permutation, then Array.reduce() to combine all permutations in one array. Base cases are for string length equal to 2 or 1.
const stringPermutations = str => { if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str]; return str .split('') .reduce( (acc, letter, i) => acc.concat(stringPermutations(str.slice(0, i) + str.slice(i + 1)).map(val => letter + val)), [] ); };
stringPermutations('abc'); // ['abc','acb','bac','bca','cab','cba']
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:
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!
Start by creating a snippet, according to the snippet template. Make sure to follow these simple guidelines:
Run npm run tagger from 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.
You can optionally test your snippet to make our job easier. Simply run npm run tester to generate the test files for your snippet. Find the related folder for you snippet under the test directory and write some tests. Remember to run npm run tester again to make sure your tests are passing.
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.
