Declare an Array in Typescript

Question

I'm having trouble either declaring or using a boolean array in Typescript, not sure which is wrong. I get an undefined error. Am I supposed to use JavaScript syntax or declare a new Array object?

Which one of these is the correct way to create the array?

private columns = boolean[];
private columns = [];
private columns = new Array<boolean>();

How would I initialize all the values to be false?

How would I access the values, can I access them like, columns[i] = true;..?

Accepted Answer

Here are the different ways in which you can create an array of booleans in typescript:

let arr1: boolean[] = [];
let arr2: boolean[] = new Array();
let arr3: boolean[] = Array();

let arr4: Array<boolean> = [];
let arr5: Array<boolean> = new Array();
let arr6: Array<boolean> = Array();

let arr7 = [] as boolean[];
let arr8 = new Array() as Array<boolean>;
let arr9 = Array() as boolean[];

let arr10 = <boolean[]> [];
let arr11 = <Array<boolean>> new Array();
let arr12 = <boolean[]> Array();

let arr13 = new Array<boolean>();
let arr14 = Array<boolean>();

You can access them using the index:

console.log(arr[5]);

and you add elements using push:

arr.push(true);

When creating the array you can supply the initial values:

let arr1: boolean[] = [true, false];
let arr2: boolean[] = new Array(true, false);

Answer 2

this is how you can create an array of boolean in TS and initialize it with false:

var array: boolean[] = [false, false, false]

or another approach can be:

var array2: Array<boolean> =[false, false, false]

you can specify the type after the colon which in this case is boolean array

Answer 3

Few ways of declaring a typed array in TypeScript are

const booleans: Array<boolean> = new Array<boolean>();
// OR, JS like type and initialization
const booleans: boolean[] = [];

// or, if you have values to initialize 
const booleans: Array<boolean> = [true, false, true];
// get a vaue from that array normally
const valFalse = booleans[1];

Answer 4

Specific type of array in typescript

export class RegisterFormComponent 
{
     genders = new Array<GenderType>();   // Use any array supports different kind objects

     loadGenders()
     {
        this.genders.push({name: "Male",isoCode: 1});
        this.genders.push({name: "FeMale",isoCode: 2});
     }
}

type GenderType = { name: string, isoCode: number };    // Specified format

Answer 5

let arr1: boolean[] = [];

console.log(arr1[1]);

arr1.push(true);

Declare an Array in Typescript

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