如何定义 object 的类型，其属性将从 TypeScript 中的数组中获取

Question

How to define type of an object whose properties are going to be fetched from an array in TypeScript.

In the following example, how can I define the type of lookUpMap object?

const arr1 = ["a", "b", "c", "d"];
const arr2 = ["x", "y", "b"];

class Arr {
    
    private lookUpMap = {}
    
    constructor(private arr1: string[], private arr2: string[]){}    
    
    linearCompare(){
        for(let i of this.arr1){
            this.lookUpMap[i] = true
        }
        
        for(let i of this.arr2){
            if(this.lookUpMap[i]){
                return console.log(true);
            }
        }
        return console.log(false);
    }
}

const arrComp = new Arr(arr1, arr2);
arrComp.linearCompare()

Thank you

Answer 1

The most straightforward type I can think of for lookupMap is a dictionary-like object with a string index signature whose properties are of type true | undefined true | undefined :

  private lookUpMap: { [k: string]: true | undefined } = {}

This will let you write true to any string-valued key, as in this.lookUpMap[i] = true , and understand that when you read from a string-valued key, the result will either be true or undefined , as in if (this.lookupMap[i]) {...} .

Note that this has nothing to do with the fact that your keys are coming from arrays; lookupMap will allow you to index into it with any string whatsoever.

Playground link to code