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


Javascript Problem Overview

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'.

The piece of code causing it is:

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

This however doesn't cause this error:

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

This doesn't make any sense to me. I would like to solve it when defining the attributes the first time. At the moment I'm writing:

private applicationsByState: Array<any> = [];

But someone mentioned that the problem is trying to use a string type as index in an array and that I should use a map. But I'm not sure how to do that.

Thans for your help!

Javascript Solutions

Solution 1 - Javascript

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;

Solution 2 - Javascript

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.

Solution 3 - Javascript

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

Solution 4 - Javascript

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) =>

Solution 5 - Javascript

In tsconfig.json


  "suppressImplicitAnyIndexErrors": true,
  "strictPropertyInitialization": false,


Solution 6 - Javascript

My function :

My function:

oldkey1: 24,
oldkey2: "word",
oldkey3: true,

object = {
oldkey1: "newkey1",
oldkey2: "newkey2",
oldkey3: "newkey3",

const updateKeys = (data: object, object:objectType): object => {

  let dataStr = JSON.stringify(data)
  Object.keys(data).forEach((key) => {
    dataStr = dataStr.replace(key, object[key])

  let newData = JSON.parse(dataStr)

  return newData;

Thank you


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Content TypeOriginal AuthorOriginal Content on Stackoverflow
QuestionOle SpaarmannView Question on Stackoverflow
Solution 1 - JavascriptNitzan TomerView Answer on Stackoverflow
Solution 2 - JavascriptRobert BrisitaView Answer on Stackoverflow
Solution 3 - JavascriptDave ت MaherView Answer on Stackoverflow
Solution 4 - JavascriptCPHPythonView Answer on Stackoverflow
Solution 5 - Javascriptrohit.khurmi095View Answer on Stackoverflow
Solution 6 - JavascriptmeguehoutView Answer on Stackoverflow