parseInt: use more concrete type for `radix` argument

Search Terms

parseInt, radix

Suggestion

From MDN docs:
radix: An integer between 2 and 36 that represents the radix
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt#Parameters

TS definition (lib.es5.d.ts):

declare function parseInt(s: string, radix?: number): number;

It will be safer to use more concrete type for radix:

type TRadix =
2|3|4|5|6|7|8|9|10|11|12|13|14|15|16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31|32|33|34|35|36

function safeParseInt(s: string, radix?: TRadix) {
  return parseInt(s, radix)
}

Use Cases

['1', '7', '11'].map(safeParseInt) // error -> Type 'number' is not assignable to type 'TRadix' ("strictFunctionTypes": true)

Examples

['1', '7', '11'].map(item) => safeParseInt(item, 10)) // OK

const config = {
  nested: {
    number: '42',
    radix: 10,
  },
} as const;
safeParseInt(config.nested.number, config.nested.radix)) // OK

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

lib.es5.d.ts の parseInt 宣言から始め、標準ライブラリの定義で radix パラメーターがどのように表現されているかを確認します。次に、提供されている safeParseInt と map の例を確認し、その上で型レベルの動作と、完了の基準となる互換性の要件を判断します。