The specified type 'IterableIterator<number>' does not belong to either an array type or a string type

Encountering an error while attempting to generate a dynamic range of numbers.

Error: Type 'IterableIterator<number>' is not recognized as an array or string type. Use the compiler option '--downlevelIteration' to enable iteration over iterators.

Faced with a similar issue before but unable to find a working solution.

TypeScript and Iterator: Type 'IterableIterator<T>' handling

My current setup includes...

  • Initialization command used: npx create-next-app@latest --ts
class FlexGrid extends React.Component {

    range(size: number, startAt = 0) {
        return [...Array(size).keys()].map(i => i + startAt);
    }

Tried adjusting settings like target: es6 and downlevelIteration: true, but the error persists.

{
  "compilerOptions": {
    "target": "es6",
    "lib": ["dom", "dom.iterable", "esnext"],
    "allowJs": true,
    "skipLibCheck": true,
    "strict": true,
    "forceConsistentCasingInFileNames": true,
    "noEmit": true,
    "esModuleInterop": true,
    "module": "esnext",
    "moduleResolution": "node",
    "resolveJsonModule": true,
    "isolatedModules": true,
    "jsx": "preserve",
    "incremental": true,
    "downlevelIteration": true
  },
  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx"],
  "exclude": ["node_modules"]
}

Answer №1

It seems to be following strict guidelines and is not allowing the creation of an array using spread from an iterator (which is not an array). However, there is a solution to this limitation by utilizing the Array.from method:

generateRange(size: number, startFrom = 0) {
  return Array.from(Array(size).keys()).map((index) => index + startFrom);
}

The Array.from function works with any data structure that is iterable.

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