元素隐式具有“ any”类型，因为类型“ xxx”没有索引签名

Question

I encounter two case about this problem when I try to refactor a es6 project in typescript, and one is about Object.keys() and the other is about import * as xxx .

Case 1:

const SUPPORTED_VALUES = {
    min_s: 'Mininum similarity',
    max_rc: 'Maximum result count'
}
const UNSUPPORTED_MSG =
    'Configurable values:\n' +
    Object.keys(SUPPORTED_VALUES)
        .map(k => `${k}: ${SUPPORTED_VALUES[k]}`)
        .join('\n')

The k in the map is guaranteed to be a key in SUPPORTED_VALUES , but typescript compiler doesn't know about this. How should I fix this without disabling noImplicitAny ?

Case 2:

I have a file called cmd.ts :

export async function cmd1(args){}
export async function cmd2(args){}

It is used is another file like this:

import * as cmdHandlers from './cmd'
// some code...
if (cmd in cmdHandlers) {
    await cmdHandlers[cmd](bot, msg, ...args)
}

This is also guaranteed that cmd exists in cmdHandlers , but typescript compiler can't handle this.

Answer 1

In case 1, you need define exactly type for SUPPORTED_VALUES like {[key: string]: string}

const SUPPORTED_VALUES: {[key: string]: string} = {
  min_s: 'Minimum similarity',
  max_rc: 'Maximum result count'
}
const UNSUPPORTED_MSG =
  'Configurable values:\n' +
  Object.keys(SUPPORTED_VALUES)
    .map(k => `${k}: ${SUPPORTED_VALUES[k]}`)
    .join('\n')

Case 2, The same case 1, cmd can be anything, but cmdHandlers only includes cmd1 and cmd2 . You can define your type for cmd.ts module to make cmdHandlers is a object with any property name.

I think it is ok, because you have a condition before call a function

// cmd.ts

async function cmd1(...args: any) { }
async function cmd2(...args: any) { }

const myExport: { [key: string]: (...args: any) => void } = {
  cmd1,
  cmd2,
}

export default myExport;

//

import cmdHandlers from './cmd'
// some code...
if (cmd in cmdHandlers) {
    await cmdHandlers[cmd](bot, msg, ...args)
}