What is the best way to declare this massive entity in typescript?

Question

What is the best way to declare this massive entity in typescript?

In the process of parsing a file, a large object is returned by the main function.

function parse(file){
/* dostuff.. */
return myObject
}

The order of determining properties is crucial (e.g., "a" must be determined before "b" or the value will be different). Here is a simple example:

type MyObject = {a:number, b:number, c:string} //long list of keys..
function parse():MyObject{
let myObject:{[key:string]:any} = { }
myObject.a = 'hello';
myObject.b = 5;
myObject.c = 55;
//...
return myObject as MyObject
}

However, myObject.a is expected to be a number but it is a string (similar issue with myObject.c). As a result, type checking becomes less effective.

How can this be improved? Perhaps by declaring each property as a const prop:type=value initially?

typescript

Answer 1

Answer №1

TypeScript has strict rules when it comes to implementing type requirements. You either have to implement all the requirements at once or make some of them optional from the start.

Implementing all requirements together would involve defining the object like this:

type MyObject = { a: string, b: number, c: number };

function main(): MyObject {
  // Gathering necessary data before creating `myObject`
  const a: string = "Hello world";
  const b: number = 42;
  const c: number = 17;

  // Creating `myObject` with all the required data
  const myObject: MyObject = { a, b, c };

  return myObject;
}

Give it a try.

The alternative approach, making some requirements optional, can be done as follows:

type MyObject = { a: string, b: number, c: number };

function main(): MyObject {
  // `myObject` exists but is not fully implemented
  const myObject: Partial<MyObject> = {};

  // Adding missing data to `myObject`
  myObject.a = "Hello world";
  myObject.b = 42;
  myObject.c = 17;

  // Return `myObject` as fully implemented, ignoring TypeScript warnings
  return myObject as MyObject;
}

Test it out.

It is recommended to use the first approach whenever feasible.

Answer 2

TypeScript has strict rules when it comes to implementing type requirements. You either have to implement all the requirements at once or make some of them optional from the start.

Implementing all requirements together would involve defining the object like this:

type MyObject = { a: string, b: number, c: number };

function main(): MyObject {
  // Gathering necessary data before creating `myObject`
  const a: string = "Hello world";
  const b: number = 42;
  const c: number = 17;

  // Creating `myObject` with all the required data
  const myObject: MyObject = { a, b, c };

  return myObject;
}

Give it a try.

The alternative approach, making some requirements optional, can be done as follows:

type MyObject = { a: string, b: number, c: number };

function main(): MyObject {
  // `myObject` exists but is not fully implemented
  const myObject: Partial<MyObject> = {};

  // Adding missing data to `myObject`
  myObject.a = "Hello world";
  myObject.b = 42;
  myObject.c = 17;

  // Return `myObject` as fully implemented, ignoring TypeScript warnings
  return myObject as MyObject;
}

Test it out.

It is recommended to use the first approach whenever feasible.

What is the best way to declare this massive entity in typescript?

Answer №1

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