TypeScript TS7015: Element implicitly has an 'any' type because index expression is not of type 'number'

Question

Im getting this compilation error in my Angular 2 app:

TS7015: Element implicitly has an \'any\' type because index expression is not of type \'number\'.


        

Answer 1

If you want a key/value data structure then don't use an array.

You can use a regular object:

private applicationsByState: { [key: string]: any[] } = {};

getApplicationCount(state: string) {
    return this.applicationsByState[state] ? this.applicationsByState[state].length : 0;
}

Or you can use a Map:

private applicationsByState: Map<string, any[]> = new Map<string, any[]>();

getApplicationCount(state: string) {
    return this.applicationsByState.has(state) ? this.applicationsByState.get(state).length : 0;
}

Answer 2

I used this to get around it so I could use the window object.

//in js code somewhere
window.DataManager = "My Data Manager";


//in strict typescript file
let test = (window as { [key: string]: any })["DataManager"] as string;
console.log(test); //output= My Data Manager

Answer 3

I was actually working with React and I got this error when I assigned an object's property through a custom key (i.e. myObj[myKey] = ). To resolve it, I simply used as keyof:

interface IMyObj { title: string; content: string; }
const myObj: IMyObj = { title: 'Hi', content: 'Hope all is well' };
const myKey: string = 'content';

myObj[myKey as keyof IMyObj] = 'All is great now!';

This explicitly tells Typescript that your custom string (myKey) belongs to the group of properties from an interface/type you used for declaring your object (myObj).

P.S.: another way to get the property's value is shown on a closed Typescript's issue on Github through extends:

interface IMyObj {
  title: string;
  content: string;
}

const myObj: IMyObj = { title: 'Hi', content: 'Hope all is well' };
const myKey: string = 'content';

const getKeyValue = <T extends object, U extends keyof T>(obj: T) => (key: U) =>
  obj[key];
console.log(getKeyValue(myObj)(myKey));

Answer 4

Not the OP's direct issue but for users encountering this error for libraries not under their control, one can suppress this error is by adding:

{
  ...
  "suppressImplicitAnyIndexErrors": true,
  ...
}

to the tsconfig.json file.