CODEWITHSUNDEEP
javascripttypescriptcastingtypeerrortypescript-typings
Shreyas Chorge
Shreyas Chorge

Reputation: 319

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

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

Upvotes: 0

Views: 150

Answers (1)

jcalz
jcalz

Reputation: 330436

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:

  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

Upvotes: 1

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