JavaScript Tutorial in Hindi #19 | Advanced Array Methods & Techniques (2025)

✅ **1. .reduce() – Reduce Array to a Single Value

Used to combine all items of an array into a single result (e.g., sum, product).

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let numbers = [10, 20, 30];

let total = numbers.reduce((acc, curr) => acc + curr, 0);
console.log(total); // 60

✅ **2. .slice() vs .splice() – Know the Difference

MethodModifies Original?Purpose
slice()❌ NoExtract a portion
splice()✅ YesAdd/Remove/Replace items


🔹 slice(start, end) – Non-destructive

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let arr = [1, 2, 3, 4];
console.log(arr.slice(1, 3)); // [2, 3]

🔹 splice(start, deleteCount, ...items) – Destructive

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let colors = ["Red", "Green", "Blue"];
colors.splice(1, 1, "Yellow");
console.log(colors); // ["Red", "Yellow", "Blue"]

✅ 3. splice(start, deleteCount, ...items) – Modify Original Array

  1. Start: index to start at
  2. DeleteCount: number of items to remove
  3. Items: new items to insert
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let fruits = ["Apple", "Banana", "Mango"];
fruits.splice(1, 0, "Orange"); // Insert at index 1
console.log(fruits); // ["Apple", "Orange", "Banana", "Mango"]

✅ 4. .concat() & .flat()

🔹 concat() – Combine arrays

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let a = [1, 2];
let b = [3, 4];
let c = a.concat(b);
console.log(c); // [1, 2, 3, 4]

🔹 flat() – Flattens nested arrays (1 level by default)

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let nested = [1, [2, 3], [4, 5]];
console.log(nested.flat()); // [1, 2, 3, 4, 5]

✅ 5. Spread Operator ...

Expands array elements individually.

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let arr = [1, 2, 3];
let newArr = [...arr, 4, 5];
console.log(newArr); // [1, 2, 3, 4, 5]

Also used in function calls:

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Math.max(...arr); // 3

✅ 6. Destructuring Arrays

Extract values from an array into variables easily.

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let [a, b, c] = [10, 20, 30];
console.log(a); // 10
console.log(c); // 30

You can also skip values:

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let [first, , third] = ["One", "Two", "Three"];
console.log(third); // "Three"