Get smart in javascript

A collection of useful JavaScript patterns and shortcuts that every developer should know. For a deeper dive, check out the MDN JavaScript Guide and JavaScript.info.

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1. Array Destructuring

Extract values from arrays or function returns cleanly using destructuring assignment:

JSfile.javascript
1function getValues() {
2    const valA = "abc";
3    const valB = "def";
4    return [valA, valB];
5}
6
7const [a, b] = getValues();
8console.log(a, b); // "abc" "def"

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2. Sorting Numbers Correctly

JavaScript's default sort() converts elements to strings. Use a compare function for numbers:

JSfile.javascript
1const nums = [2, 20, 10];
2nums.sort((x, y) => x - y);
3console.log(nums); // [2, 10, 20]

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3. Remove Duplicates

Use Set to quickly remove duplicate values from an array:

JSfile.javascript
1const arr = [1, 2, 2, 3];
2const uniqueArr = [...new Set(arr)];
3console.log(uniqueArr); // [1, 2, 3]

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4. Cloning Objects

Shallow Clone

Copies only the first level of properties:

JSfile.javascript
1const obj = {
2    a: "hello",
3    b: "hello again",
4    c: { d: "new hello", e: "new hello again" }
5};
6
7const clone1 = { ...obj };

Deep Clone

structuredClone creates a true deep copy, handling nested objects, arrays, dates, and more:

JSfile.javascript
1const deepClone = structuredClone(obj);
2deepClone.c.d = "new deep hello";
3console.log(obj.c.d); // "new hello"
4console.log(deepClone.c.d); // "new deep hello"

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5. Creating Arrays

1D Array

JSfile.javascript
1const oneD = new Array(10).fill(2);
2// [2, 2, 2, 2, 2, 2, 2, 2, 2, 2]

2D Array

JSfile.javascript
1const twoD = Array.from({ length: 3 }, () => Array(5).fill(0));
2// [[0,0,0,0,0], [0,0,0,0,0], [0,0,0,0,0]]

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6. Array Testing: some() & every()

• some() — returns true if at least one element passes the test
• every() — returns true if all elements pass the test

JSfile.javascript
1const arrOne = [1, 2, 3, 4];
2const hasEven = arrOne.some((value) => value % 2 === 0);  // true
3const allEven = arrOne.every((value) => value % 2 === 0); // false

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7. Finding Min & Max

Use the spread operator with Math.min() and Math.max():

JSfile.javascript
1const numsOne = [1, 2, 3, 5];
2const mini = Math.min(...numsOne); // 1
3const maxi = Math.max(...numsOne); // 5

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8. Easy Variable Swap

Swap two variables without a temporary variable:

JSfile.javascript
1let aa = 10;
2let bb = 20;
3[aa, bb] = [bb, aa];
4// aa = 20, bb = 10

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9. Object to Array Conversions

Extract keys, values, or entries from objects:

JSfile.javascript
1const obj = { a: 1, b: 2, c: 3 };
2
3const keys = Object.keys(obj);     // ["a", "b", "c"]
4const values = Object.values(obj); // [1, 2, 3]
5const entries = Object.entries(obj); // [["a", 1], ["b", 2], ["c", 3]]

10. Swap Object Keys and Values

Swap object keys and values using Object.entries() and Object.fromEntries():

• Object.entries() returns an array of [key, value] pairs.
• Object.fromEntries() creates an object from an array of [key, value] pairs.

JSfile.javascript
1const roles = { admin: 1, user: 2, guest: 3 };
2const swapped = Object.fromEntries(
3    Object.entries(roles).map(([key, value]) => [value, key])
4);
5console.log(swapped); // { 1: "admin", 2: "user", 3: "guest" }

11. Capitalize First Letter

This pattern splits text into words, capitalizes the first letter while preserving the rest, then joins them back :

JSfile.javascript
1const text = 'hello world from javascript';
2const capitalized = text.split(' ')
3  .map(word => word[0].toUpperCase() + word.slice(1))
4  .join(' ');
5console.log(capitalized);
6// 'Hello World From Javascript'