Typescript - An index expression argument must be of type 'string', 'number', 'symbol' or 'any'

Question

I am using Typescript 1.7.5 and I encountered the An index expression argument must be of type 'string', 'number', or 'any' error on the following situation:

const settings: any = {};

_.forEach(data, (d, name: string) => { //data is just an object
    settings[name] = {};

    const colors = ColorGenerator.generateColors(Object.keys(d.ch).length);

    _(d.ch)
          .keys()
          .zip(colors)
          .forEach(([channel, color]) => {
              // name and channel are both strings
              settings[name][channel] = { // this line is throwing the error
                  channel,
                  color,
                  visible: true
              };
          }).value();
});

Is it the channel variable that's causing the error? How can I type it and destructure it at the same time?

PS I have omitted unnecessary code so if something is not making sense let me know.

Answer 1

It seems that TypeScript is not able to guess types properly, so we can help it with explicit type declaration:

// .forEach( ([channel, color]) => {
.forEach( ([channel, color]: [string, string]) => {

maybe even, if the type of colors will be more specific, eg:

const colors: any [] = ...

should help to assure, that indexes/keys channel and color of supported types