Javascript Snippets for you - #4

4th edition of 50 JS snippets served weekly for you.

Abhiraj Bhowmick

2 years ago | 2 min read

Hello my fellow readers!
If you have really come this far in this series of posts, I would like to thank you for your support in reading all of the posts in this series. Thank you and do follow me on Twitter for more tech content soon. Let's get started.

1️⃣ Drop Elements
This snippet returns a new array with n elements removed from the left.

const drop = (arr, n = 1) => arr.slice(n);

drop([1, 2, 3]); // [2,3]
drop([1, 2, 3], 2); // [3]
drop([1, 2, 3], 42); // []

2️⃣ dropRight
This snippet returns a new array with n elements removed from the right.

const dropRight = (arr, n = 1) => arr.slice(0, -n);

dropRight([1, 2, 3]); // [1,2]
dropRight([1, 2, 3], 2); // [1]
dropRight([1, 2, 3], 42); // []

3️⃣ dropRightWhile
This snippet removes elements from the right side of an array until the passed function returns true.

const dropRightWhile = (arr, func) => {
while (arr.length > 0 && !func(arr[arr.length - 1])) arr = arr.slice(0, -1);
return arr;
};

dropRightWhile([1, 2, 3, 4], n => n < 3); // [1, 2]

4️⃣ dropWhile
This snippet removes elements from an array until the passed function returns true.

const dropWhile = (arr, func) => {
while (arr.length > 0 && !func(arr[0])) arr = arr.slice(1);
return arr;
};

dropWhile([1, 2, 3, 4], n => n >= 3); // [3,4]

5️⃣ elementContains
This snippet checks whether the parent element contains the child.

const elementContains = (parent, child) => parent !== child && parent.contains(child);

elementContains(document.querySelector('head'), document.querySelector('title')); // true
elementContains(document.querySelector('body'), document.querySelector('body')); // false

6️⃣ Filter Duplicate Elements
This snippet removes duplicate values in an array.

const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));

filterNonUnique([1, 2, 2, 3, 4, 4, 5]); // [1, 3, 5]

7️⃣ findKey
This snippet returns the first key that satisfies a given function.

const findKey = (obj, fn) => Object.keys(obj).find(key => fn(obj[key], key, obj));

findKey(
{
barney: { age: 36, active: true },
fred: { age: 40, active: false },
pebbles: { age: 1, active: true }
},
o => o['active']
); // 'barney'

8️⃣ findLast
This snippet returns the last element for which a given function returns a truthy value.

const findLast = (arr, fn) => arr.filter(fn).pop();

findLast([1, 2, 3, 4], n => n % 2 === 1); // 3

9️⃣ insertAfter
This snippet can be used to insert an HTML string after the end of a particular element.

const insertAfter = (el, htmlString) => el.insertAdjacentHTML('afterend', htmlString);

insertAfter(document.getElementById('myId'), '<p>after</p>'); // <div id="myId">...</div> <p>after</p>

🔟 insertBefore
This snippet can be used to insert an HTML string before a particular element.

const insertBefore = (el, htmlString) => el.insertAdjacentHTML('beforebegin', htmlString);

insertBefore(document.getElementById('myId'), '<p>before</p>'); // <p>before</p> <div id="myId">...</div>

Thank you for reading!

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Abhiraj

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Abhiraj Bhowmick

I make stuff on the web and write blogs about it.