Expose isArrayType, isTupleType, isArrayLikeType in TypeChecker #37711

Search Terms

isArrayType, isTupleType, isArrayLikeType

Suggestion

Expose isArrayType, isTupleType, isArrayLikeType in the TypeChecker interfaace

Use Cases

Today, a consumer of the TypeScript compiler API must roll their own implementation of these functions (or call into a type checker's private API) to validate some type. It would be convenient if these functions were exposed publicly instead.

This is somewhat related to #9879 but is of a much smaller scope -- here we only wish to provide comparison methods for array-like and tuple types.

Examples

Current:

import * as ts from 'typescript';

function isArrayType(type: Type, checker: ts.TypeChecker): boolean {
  return (checker as any).isArrayType(type);
}

let ty: ts.Type = makeType();
if (isArrayType(ty)) {
  // do some array things
}

Suggested:

let ty: ts.Type = makeType();
let checker: ts.TypeChecker = getTypeChecker();
if (checker.isArrayType(ty)) {
  // do some array things
}

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.