logo 30 seconds of code

Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.

302
snippets

115
contributors

3168
commits

19804
stars

Our 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:

sortedLastIndex

Returns the highest index at which value should be inserted into array in order to maintain its sort order.

Check if the array is sorted in descending order (loosely). Use Array.reverse() and Array.findIndex() to find the appropriate last index where the element should be inserted.

const sortedLastIndex = (arr, n) => {
  const isDescending = arr[0] > arr[arr.length - 1];
  const index = arr.reverse().findIndex(el => (isDescending ? n <= el : n >= el));
  return index === -1 ? 0 : arr.length - index;
};

sortedLastIndex([10, 20, 30, 30, 40], 30); // 4

unfold

Builds an array, using an iterator function and an initial seed value.

Use a while loop and Array.push() to call the function repeatedly until it returns false. The iterator function accepts one argument (seed) and must always return an array with two elements ([value, nextSeed]) or false to terminate.

const unfold = (fn, seed) => {
  let result = [],
    val = [null, seed];
  while ((val = fn(val[1]))) result.push(val[0]);
  return result;
};

var f = n => (n > 50 ? false : [-n, n + 10]);
unfold(f, 10); // [-10, -20, -30, -40, -50]

zipObject

Given an array of valid property identifiers and an array of values, return an object associating the properties to the values.

Since an object can have undefined values but not undefined property pointers, the array of properties is used to decide the structure of the resulting object using Array.reduce().

const zipObject = (props, values) =>
  props.reduce((obj, prop, index) => ((obj[prop] = values[index]), obj), {});

zipObject(['a', 'b', 'c'], [1, 2]); // {a: 1, b: 2, c: undefined}
zipObject(['a', 'b'], [1, 2, 3]); // {a: 1, b: 2}

Getting started


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:


Top contributors

chalarangelo Angelos Chalaris
fejes713 Stefan Feješ
flxwu Felix Wu
atomiks atomiks
kingdavidmartins King David Martins
kriadmin Rohit Tanwar
iamsoorena Soorena Soleimani
skatcat31 Robert Mennell

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!

1

Create

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.
2

Tag

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.

3

Test

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.

4

Pull 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.