TypeScript Array

A typescript array can store multiple values of different data types sequentially, similar to other programming languages.

In this post, we will learn to create an array, clone array, merge arrays and iterate through array elements in TypeScript with easy-to-follow examples.

Table of Contents

Create Array
Iterate Through Array
Clone Array
Merge Arrays

1. Creating a TypeScript Array

Like JavaScript, TypeScript has an array type to allow the assignment of multiple values. The array is specified by adding a square bracket after the type.

To use the type-safety capability of TypeScript, we can add diamond brackets to specify the type of the elements in the array. Every time a new value is added to such a generic array, the compiler checks for type compatibility and alerts if there is a type mismatch.

//Various ways to declare a typed array
let myArr1: boolean[];
let myArr2: boolean[] = [];
let myArr3: boolean[] = new Array();
let myArr4: boolean[] = Array();

//Initializing an array
myArr1 = [false, false, true];



let flags: boolean[] = [false, false, true];	

//or

let flags: Array<boolean> = [false, false, true];



let scores: number[] = [10, 20, 30, 40];	

//or

let scores: Array<number> = [10, 20, 30, 40];	

Add elements to array

To add more elements to array, use push() method.

//array of numbers
let scores: number[] = [10, 20, 30, 40];

scores.push( 50 );	//[10, 20, 30, 40, 50]

scores.push( 'abc' );	//data.ts(24,14): error TS2345: Argument of type '"abc"' is not  
						//assignable to parameter of type 'number'.

2. Iterating through an Array

We can use either for loops to iterate over array elements.

2.1. Using “for…of” loop

let scores :number[] = [10, 20, 30, 40];	

for (var score of scores) {
	console.log(score);		//Outputs 10 20 30 40
}

2.2. Using traditional for loop

let scores :number[] = [10, 20, 30, 40];	

for (var i = 0; i < scores.length; i++) {
	console.log(scores[i]);		//Outputs 10 20 30 40
}

3. Cloning an Array

Use spread operator to clone array. It is the easiest and the most recommended way.

let origScores: number[] = [10, 20, 30];	

let clonedScores: number[] = [...origScores];

console.log(clonedScores);		//[10, 20, 30]

origScores.push( 40 );

console.log(origScores);		//[10, 20, 30, 40] is "changed"
console.log(clonedScores);		//[10, 20, 30] 	is "unchanged"

4. Merging two Arrays

Use spread operator for merging arrays as well. It’s simplest and recommended way.

let scores1: number[] = [10, 20, 30];	
let scores2: number[] = [40, 50, 60];	

let mergedScore = [...scores1, ...scores2];

console.log(mergedScore);	//[ 10, 20, 30, 40, 50, 60 ]

Drop me your questions in the comments section.

Happy Learning !!