Improve type definitions and move tests to TS (#37)

karma.conf.cjs

@@ -22,18 +22,29 @@ module.exports = function(config) {
         ],
 
         // list of files / patterns to load in the browser
-        files: [{ pattern: 'test/{browser,common}.test.js', watched: false }],
+        files: [{ pattern: 'test/{browser,common}.test.ts', watched: false }],
 
         // list of files / patterns to exclude
         exclude: [],
 
         // preprocess matching files before serving them to the browser
         // available preprocessors: https://www.npmjs.com/search?q=keywords:karma-preprocessor
         preprocessors: {
-            'test/{browser,common}.test.js': 'webpack'
+            'test/{browser,common}.test.ts': 'webpack'
         },
 
-        webpack: {},
+        webpack: {
+            resolve: {
+                extensions: ['', '.js', '.ts']
+            },
+            module: {
+                rules: [{
+                    test: /\.ts?$/,
+                    loader: 'ts-loader',
+                    options: { compilerOptions: { noEmit: false } }
+                }]
+            }
+        },
 
         // available reporters: https://www.npmjs.com/search?q=keywords:karma-reporter
         reporters: ['mocha'],

lib/index.d.ts

@@ -8,4 +8,19 @@ export type NodeWebStream<T extends Data> = NodeWebReadableStream<T>;
 type Stream<T extends Data> = WebStream<T> | NodeWebStream<T>;
 type MaybeStream<T extends Data> = T | Stream<T>;
 
-export function readToEnd<T extends Data, R extends any = T>(input: MaybeStream<T>, join?: (chunks: T[]) => R): Promise<R>;
+export function readToEnd<T extends Data, JoinFn extends (chunks: T[]) => any = (chunks: T[]) => T>(
+  input: MaybeStream<T>,
+  join?: JoinFn
+): Promise<ReturnType<JoinFn>>;
+
+export function toStream<T extends Data, InputType extends MaybeStream<T>>(
+  input: InputType
+): InputType extends T ? Stream<InputType> : InputType;
+
+export function isStream<T extends Data>(input: MaybeStream<T>): input is Stream<T>;
+
+export function slice<T extends Data, InputType extends MaybeStream<T>>(
+  input: InputType,
+  begin: number,
+  end?: number | typeof Infinity
+): InputType; // same as 'typeof input'