Interesting Facts about JavaScript Arrays
Last Updated : 10 Nov, 2024
Let us talk about some interesting facts about JavaScript Arrays that can make you an efficient programmer.
Arrays are Objects
JavaScript arrays are actually specialized objects, with indexed keys and special properties. They have a length property and are technically instances of the Array constructor.
JavaScript const a = [10, 20, 30]; console.log(typeof a);
You can add non-integer properties to arrays, making them work partly like objects. However, this is usually discouraged for clarity.
JavaScript let a = [1, 2, 3]; // Adding a property to array (NOT RECOMMEMDED IN PRACTICE) a.name = "MyArray"; console.log(a.name); // Iterating through the array with `for...in` // (NOT RECOMMENDED IN PRACTICE) for (let key in a) { console.log(`${key}: ${a[key]}`); } OutputMyArray 0: 1 1: 2 2: 3 name: MyArray
Mixed Elements Allowed
Like Python and unlike C/C++/Java,, we can have mixed type of elements in a JavaScript array.
JavaScript const a = [10, "hi", true]; console.log(a);
Dynamic Size
Like Python and unlike C/C++/Java,, the default array implementation is Dynamic Size.
JavaScript let a = [1, 2, 3]; a.push(4); console.log(a);
Negative Indexing
The .at() method, introduced in ES2022, allows access to array elements using negative indices, making it easy to retrieve elements from the end of an array without calculating the length.
JavaScript const arr = [10, 20, 30]; console.log(arr.at(-1));
Resizing an Array
We can resize a JavaScript array by simply changing its length property.
JavaScript let a = [1, 2, 3, 4]; a.length = 2; console.log(a);
Array Assignment
When we assign an array to another, it only creates one more reference to the same array.
JavaScript // changed the original array let a = [10, 20]; let b = a; b.push(30); console.log(a);
Spread Operator
We get members of an array or a string. It helps us in copying in copying an array, concatenating arrays and passing array elements to different parameters of a function.
JavaScript // Arrat copy using spread operator let a = [10, 20]; let b = [...a]; b.push(30); console.log(a);
// Array concatenation using spread operator let a = [10, 20]; let b = [30, 40]; let c = [...a, ...b] console.log(c);
function add(x, y, z) { return x + y + z; } let a = [10, 20, 30]; console.log(add(...a)); Empty Elements in Array
JavaScript allows empty elements in an array. When we access these elements, we get undefined.
JavaScript const a = [1, , , 3]; console.log(a); console.log(a[1]);
Output[ 1, <2 empty items>, 3 ] undefined
JavaScript const a = [1, 3]; a.length = 4 console.log(a); console.log(a[2]);
Output[ 1, 3, <2 empty items> ] undefined
Direct Methods to Modify Arrays
JavaScript allows multiple direct methods for efficient programming.
JavaScript const a = [1, 2, 3, 4]; const b = a.map(x => x * 2); console.log(b) const c = a.filter(x => x > 2); console.log(c) const d = [1, [2, 3], [4, [5]]]; console.log(d.flat(2));
Output[ 2, 4, 6, 8 ] [ 3, 4 ] [ 1, 2, 3, 4, 5 ]
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