Better types for UrlSearchParams

Suggestion

🔍 Search Terms

Restrictive typing on UrlSearchParams

✅ Viability 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, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

declare var URLSearchParams: {
    prototype: URLSearchParams;
    // new(init?: string[][] | Record<string, string> | string | URLSearchParams): URLSearchParams;
    new(init?: 
        | string
        | URLSearchParams
        | Record<string | number, string | number | boolean | string[] | number[] | boolean[]>
        | [string | number | boolean, string | number | boolean | string[] | number[] | boolean[]][]): URLSearchParams;
    toString(): string;
};

📃 Motivating Example

The actual typing design is more restrictive than the Javascript runtime itself.

💻 Use Cases

More possibilities to create strict typed UrlSearchParams objects:

let url = 'https://developer.microsoft.com'

const queryParams = new UrlSearchParams({
  key1: ["v1", "v2"],
  key2: ["v1", "v2", "v3"]
})

url = url + '?' + queryParams // https://developer.microsoft.com?key1=v1,v2&key2=v1,v2,v3

Start by locating the standard-library declaration for URLSearchParams and review its constructor typing against the proposed overload and motivating examples. Check the surrounding type definitions and relevant type tests before deciding the supported input shapes; done means the declarations accept the intended stricter forms without changing emitted JavaScript or runtime behavior.