What is the best way to add elements to a custom-defined array?

Question

What is the best way to add elements to a custom-defined array?

I am currently utilizing Angular 5 with typescript version 2.7.1. Within typescript, I have created a custom type:

 arr: {id: string; name: string; }[];

I am attempting to add an element to the array and have experimented with the following methods:

this.arr.push({id: "text", name: "text"})

However, I encountered the following error: TypeError: Cannot read property 'push' of undefined

let array2 : {id: "id", name: "name"}
this.arr.push(array2)

Again, I received the same error message: TypeError: Cannot read property 'push' of undefined

I am puzzled as to why this is not functioning as expected. I am clearly defining id and name within the push operation. Can anyone provide insight into what I might be missing?

arrays angular typescript

Answer 1

Answer №1

Before utilizing the field, make sure to initialize the array as empty:

this.items = [];

Alternatively, you can initialize it upon declaration:

items: {id: number; title: string; }[] = [];

Answer 2

Before utilizing the field, make sure to initialize the array as empty:

this.items = [];

Alternatively, you can initialize it upon declaration:

items: {id: number; title: string; }[] = [];

Answer 3

Answer №2

When I came across this issue, it wasn't immediately obvious that the array needed to be initialized. Once you do that, the array can start accepting objects of its type:

    type person = {id: string, name: string}
    
    const peopleList: person[] =[];
    const newPerson: person = {id: "123", name: "John"}

    peopleList.push(newPerson);
    console.log(peopleList) // outputs [{id: "123", name: "John"}]

Check out this Typescript Playground Example

Answer 4

When I came across this issue, it wasn't immediately obvious that the array needed to be initialized. Once you do that, the array can start accepting objects of its type:

    type person = {id: string, name: string}
    
    const peopleList: person[] =[];
    const newPerson: person = {id: "123", name: "John"}

    peopleList.push(newPerson);
    console.log(peopleList) // outputs [{id: "123", name: "John"}]

Check out this Typescript Playground Example

What is the best way to add elements to a custom-defined array?

Answer №1

Answer №2

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