JavaScript array methods you will use every day

These methods replace most hand-written for loops, and they make your intent clear.

const students = [
  { name: 'Asha', branch: 'CSE', cgpa: 8.7 },
  { name: 'Ravi', branch: 'ECE', cgpa: 7.4 },
  { name: 'Meena', branch: 'CSE', cgpa: 9.1 }
];
const names = students.map(s => s.name);
const cse = students.filter(s => s.branch === 'CSE');
const avg = students.reduce((sum, s) => sum + s.cgpa, 0) / students.length;
const topper = students.find(s => s.cgpa > 9);
console.log(names.join(', '));
console.log(cse.length, avg.toFixed(2), topper.name);
console.log(students.some(s => s.cgpa < 7.5), students.every(s => s.cgpa >= 7));

Asha, Ravi, Meena
2 8.40 Meena
true true

• map: same length, each item transformed.
• filter: only the items that pass a test.
• reduce: folds everything into one value. Always give it a starting value (0 above).
• find: the first match, or undefined. findIndex gives its position.
• some / every: does at least one, or does every item, pass the test.

The sort mistake

Without a compare function, sort turns items into strings and compares them as text. It also changes the original array.

const marks = [100, 25, 9, 70];
console.log([...marks].sort().join(' '));
console.log([...marks].sort((a, b) => a - b).join(' '));
console.log(marks.join(' '));

100 25 70 9
9 25 70 100
100 25 9 70

Copy the array first ([...marks]) when you need the original order later. Newer engines also offer toSorted(), which returns a sorted copy.

Chaining

Because map and filter return new arrays, you can chain them: students.filter(s => s.branch === 'CSE').map(s => s.name) gives the CSE names in one readable line.