ts-transformer-keys

A TypeScript custom transformer which enables to obtain keys of given type.

Requirement

TypeScript >= 2.4.1

How to use this package

This package exports 2 functions. One is keys which is used in TypeScript codes to obtain keys of given type, while the other is a TypeScript custom transformer which is used to compile the keys function correctly.

How to use keys

import { keys } from 'ts-transformer-keys';

interface Props {
  id: string;
  name: string;
  age: number;
}
const keysOfProps = keys<Props>();

console.log(keysOfProps); // ['id', 'name', 'age']

How to use the custom transformer

Unfortunately, the only way currently available to use custom transformers is to use them with TypeScript compiler API (See microsoft/TypeScript#14419 for detail). Something like the following works.

const ts = require('typescript');
const keysTransformer = require('ts-transformer-keys/transformer').default;

const program = ts.createProgram([/* your files to compile */], {
  strict: true,
  noEmitOnError: true,
  target: ts.ScriptTarget.ES5
});

const transformers = {
  before: [keysTransformer(program)],
  after: []
};
const { emitSkipped, diagnostics } = program.emit(undefined, undefined, undefined, false, transformers);

if (emitSkipped) {
  throw new Error(diagnostics.map(diagnostic => diagnostic.messageText).join('\n'));
}

As a result, the TypeScript code shown above is compiled into the following JavaScript.

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var ts_transformer_keys_1 = require("ts-transformer-keys");
var keysOfProps = ["id", "name", "age"];
console.log(keysOfProps); // ['id', 'name', 'age']

Note

• The keys function can only be used as a call expression. Writing something like keys.toString() results in a runtime error.
• keys does not work with a dynamic type parameter, i.e., keys<T>() in the following code is converted to an empty array([]).

class MyClass<T extends object> {
  keys() {
    return keys<T>();
  }
}

License

MIT