I am creating an array of objects in TypeScript:
userTestStatus xxxx = {
"0": { "id": 0, "name": "Available" },
"1": { "id": 1, "name": "Ready" },
"2": { "id": 2, "name": "Started" }
};
Can someone tell me how I could declare its type correctly? Is it possible to do inline or would I need two definitions?
I'm looking to replace the xxx with a type declaration, so that later on TypeScript would alert me if I used something like userTestStatus[3].nammme by mistake.
You are better off using a native array instead of an object literal with number-like properties, so that numbering (as well as numerous other array functions) are taken care of off-the-shelf.
What you are looking for here is an inline interface definition for your array that defines every element in that array, whether initially present or introduced later:
let userTestStatus: { id: number, name: string }[] = [
{ "id": 0, "name": "Available" },
{ "id": 1, "name": "Ready" },
{ "id": 2, "name": "Started" }
];
userTestStatus[34978].nammme; // Error: Property 'nammme' does not exist on type [...]
If you are initializing your array with values right away, the explicit type definition is not a necessity; TypeScript can automatically infer most element types from the initial assignment:
let userTestStatus = [
{ "id": 0, "name": "Available" },
...
];
userTestStatus[34978].nammme; // Error: Property 'nammme' does not exist on type [...]
What you have above is an object, not an array.
To make an array use [ & ] to surround your objects.
userTestStatus = [
{ "id": 0, "name": "Available" },
{ "id": 1, "name": "Ready" },
{ "id": 2, "name": "Started" }
];
Aside from that TypeScript is a superset of JavaScript so whatever is valid JavaScript will be valid TypeScript so no other changes are needed.
Feedback clarification from OP... in need of a definition for the model posted
You can use the types defined here to represent your object model:
type MyType = {
id: number;
name: string;
}
type MyGroupType = {
[key:string]: MyType;
}
var obj: MyGroupType = {
"0": { "id": 0, "name": "Available" },
"1": { "id": 1, "name": "Ready" },
"2": { "id": 2, "name": "Started" }
};
// or if you make it an array
var arr: MyType[] = [
{ "id": 0, "name": "Available" },
{ "id": 1, "name": "Ready" },
{ "id": 2, "name": "Started" }
];
Some tslint rules are disabling use of [], example message: Array type using 'T[]' is forbidden for non-simple types. Use 'Array<T>' instead.
Then you would write it like:
var userTestStatus: Array<{ id: number, name: string }> = Array(
{ "id": 0, "name": "Available" },
{ "id": 1, "name": "Ready" },
{ "id": 2, "name": "Started" }
);
If you're looking for something that behaves like an enumeration (because I see you are defining an object and attaching a sequential ID 0, 1, 2 and contains a name field that you don't want to misspell (e.g. name vs naaame), you're better off defining an enumeration because the sequential ID is taken care of automatically, and provides type verification for you out of the box.
enum TestStatus {
Available, // 0
Ready, // 1
Started, // 2
}
class Test {
status: TestStatus
}
var test = new Test();
test.status = TestStatus.Available; // type and spelling is checked for you,
// and the sequence ID is automatic
The values above will be automatically mapped, e.g. "0" for "Available", and you can access them using TestStatus.Available. And Typescript will enforce the type when you pass those around.
You wanted an array of objects, (not exactly an object with keys "0", "1" and "2"), so let's define the type of the object, first, then a type of a containing array.
class TestStatus {
id: number
name: string
constructor(id, name){
this.id = id;
this.name = name;
}
}
type Statuses = Array<TestStatus>;
var statuses: Statuses = [
new TestStatus(0, "Available"),
new TestStatus(1, "Ready"),
new TestStatus(2, "Started")
]
You can also try
interface IData{
id: number;
name:string;
}
let userTestStatus:Record<string,IData> = {
"0": { "id": 0, "name": "Available" },
"1": { "id": 1, "name": "Ready" },
"2": { "id": 2, "name": "Started" }
};
To check how record works: https://www.typescriptlang.org/docs/handbook/utility-types.html#recordkt
Here in our case Record is used to declare an object whose key will be a string and whose value will be of type IData so now it will provide us intellisense when we will try to access its property and will throw type error in case we will try something like userTestStatus[0].nameee
A little old but I felt I could add some clarity to this.
Exact Answer
interface MyObject {
id: number;
name: string;
}
interface MyExactData {
[key: string]: MyObject;
}
let userTestStatus: MyExactData = {
"0": { "id": 0, "name": "Available" },
"1": { "id": 1, "name": "Ready" },
"2": { "id": 2, "name": "Started" }
};
But the above is not how we usually do an array of objects, you would use the simple native array in javaScript.
interface MyObject { // define the object (singular)
id: number;
name: string;
}
let userTestStatus_better: MyObject[] = [
{ "id": 0, "name": "Available" },
{ "id": 1, "name": "Ready" },
{ "id": 2, "name": "Started" }
];
Simply adding [] to our interface provides the typing for an array of said objects.
And to do that inline
let userTestStatus_inline: {id:number, name:string}[] = [
{ "id": 0, "name": "Available" },
{ "id": 1, "name": "Ready" },
{ "id": 2, "name": "Started" }
];
I would use the interface as you have something that is definable, understandable, and reusable. If you need to make changes, you can make changes to the one interface and typescript will report your interface to code mismatches.
