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angulartypescriptdynamic

Typescript reach defined type from variable in Angular

interface Bus  {
  id: number;
  test?: string;
}

interface Area{
  id: number;
  load?: string;
}

type TypeMap= {
  Bus: Bus,
  Area: Area,
  // etc
}



  func1(){
    const equipmentType1 = "Bus"
    const equipmentType2 = this.getSelectedEquipmentType()

    type myType1 = TypeMap[typeof equipmentType1];
    type myType2 = TypeMap[typeof equipmentType2]; // this line throw an error which is "Type TypeMap has no matching index signature for type string"


    let myObj1: myType1 = {id:1};
    let myObj2: myType1 = {id:1,test:"1"};
    let myObj3: myType1 = {test:"1"};


  }


  getSelectedEquipmentType(){
    return "Bus"
  }

In my case, I'll have different types like Bus, Area an etc. I want to create variable in this types according to selected type. So if my equipment type is Bus I want to create a variable in type Bus. But I want to do it dynamic way. So I have selected type as a string like "Bus". When I create equipmentType1 as const I can do that because equipmentType1's type is automatically defined as a Bus. But for equipmentType2, its type defined as a string and it throws an error. But I need to use it like equipmentType2. Because I'll set equipmentType in another function and I'll reach like

 const equipmentType2 = this.getSelectedEquipmentType()

I also tried interface instead of Type but result hasn't changed.

So how can achieve this or is there a better way?

Thanks in advanced!

Solution

  • You have to set keyof TypeMap for the variables, then it will access the index type.

    interface Bus  {
  id: number;
  test?: string;
}

interface Area{
  id: number;
  load?: string;
}

type TypeMap= {
  Bus: Bus,
  Area: Area,
  // etc
}

function getSelectedEquipmentType(): keyof TypeMap {
  return 'Area';
}

function func1(){
  const equipmentType1: keyof TypeMap = "Bus"
  const equipmentType2: keyof TypeMap = getSelectedEquipmentType()
  type myType1 = TypeMap[typeof equipmentType1];
  type myType2 = TypeMap[typeof equipmentType2]; // this line throw an error which is "Type TypeMap has no matching index signature for type string"
  let myObj1: myType1 = {id:1};
  let myObj2: myType1 = {id:1,test:"1"};
  let myObj3: myType2 = {id:1, load: 'test'};
}

    Typescript Playground