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ts-transformer-enumerate
A TypeScript custom transformer which enables enumerating members of the union of string literal types.
Requirement
TypeScript >= 2.4.1
How to use this package
This package exports 2 functions.
One is enumerate
which is used in TypeScript codes to enumerate members of the union of string literal types, while the other is a TypeScript custom transformer which is used to compile the enumerate
function correctly.
How to use enumerate
import { enumerate } from 'ts-transformer-enumerate';
type Colors = 'green' | 'yellow' | 'red';
const Colors = enumerate<Colors>();
console.log(Colors.green); // 'green'
console.log(Colors.yellow); // 'yellow'
console.log(Colors.red); // 'red'
How to use the custom transformer
Unfortunately, TypeScript itself does not currently provide any easy way to use custom transformers (See https://github.com/Microsoft/TypeScript/issues/14419 for detail). It is recommended to use the custom transformer with webpack, Rollup, or ttypescript as described. You can also use the transformer with TypeScript compiler API as follows.
const ts = require('typescript');
const enumerateTransformer = require('ts-transformer-enumerate/transformer').default;
const program = ts.createProgram([/* your files to compile */], {
strict: true,
noEmitOnError: true,
target: ts.ScriptTarget.ES5
});
const transformers = {
before: [enumerateTransformer(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_enumerate_1 = require("ts-transformer-enumerate");
var Colors = { green: "green", yellow: "yellow", red: "red" };
console.log(Colors.green); // 'green'
console.log(Colors.yellow); // 'yellow'
console.log(Colors.red); // 'red'
Note
- The
enumerate
function can only be used as a call expression. Writing something likeenumerate.toString()
results in a runtime error. enumerate
does not work with a dynamic type parameter, i.e.,enumerate<T>()
in the following code is converted to an empty object({}
).
class MyClass<T extends string> {
enumerate() {
return enumerate<T>();
}
}
License
MIT