Update types + add TS tests

CONTRIBUTING.md

@@ -84,10 +84,16 @@ $ yarn run test-browser-ie
 
 ### Types
 
-We validate our TypeScript `index.d.ts` with:
+We validate our TypeScript `index.d.ts` with two steps:
 
 ```sh
+# Runs the TypeScript compiler over our types
+$ yarn run test-tsc
+
+# Runs our types through a sample TypeScript file
 $ yarn run test-ts
+# Compiled output is put into a co-located index.js
+# Treat the output like a snapshot, commit any changes
 ```
 
 ### Style
@@ -135,7 +141,13 @@ please flag to your reviewers and have a discussion about whether or not the siz
 
 _Only for project administrators_
 
-1. Run `npm version patch` (or `minor|major|VERSION`) to run tests and lint,
-   build published directories, then update `package.json` + add a git tag.
-2. Run `npm publish` and publish to NPM if all is well.
-3. Run `git push && git push --tags`
+```sh
+# (1) Run tests, lint, build published dir, update package.json
+$ npm version [patch|minor|major|<version>]
+
+# (2) If all is well, publish the new version to the npm registry
+$ npm publish
+
+# (3) Then, update github with the associated tag
+$ git push && git push --tags
+```

index.d.ts

@@ -1,3 +1,3 @@
-declare function isEqual(a: any, b: any): boolean;
+declare function isEqual<A = any, B = any>(a: A, b: B): boolean;
 declare namespace isEqual {}
 export = isEqual;

package.json

@@ -10,10 +10,11 @@
     "test-browser": "karma start test/browser/karma.conf.js",
     "test-browser-ie": "karma start test/browser/karma.conf.ie.js",
     "test-node": "mocha \"test/node/*.spec.js\"",
-    "test-node-cov": "nyc mocha \"test/node/*.spec.js\"",
-    "test-ts": "tsc --target ES5 --noImplicitAny index.d.ts",
-    "test": "builder concurrent --buffer eslint test-ts test-node-cov test-browser",
-    "test-ie": "builder concurrent --buffer eslint test-ts test-node-cov test-browser-ie",
+    "test-node-cov": "nyc yarn test-node",
+    "test-ts": "tsc --p test/typescript/index.ts",
+    "test-tsc": "tsc --target ES5 --noImplicitAny index.d.ts",
+    "test": "builder concurrent --buffer eslint test-tsc test-ts test-node-cov test-browser",
+    "test-ie": "builder concurrent --buffer eslint test-tsc -test-ts test-node-cov test-browser-ie",
     "compress": "terser --compress --mangle=\"toplevel:true\" -- index.js",
     "size-min-gz": "yarn -s compress | gzip -9 | wc -c"
   },

test/typescript/index.js

@@ -0,0 +1,13 @@
+// Test file for types in typescript!
+// =============
+// An example of `equal` usage that currently breaks:
+// https://github.com/FormidableLabs/react-fast-compare/issues/61
+// @types/react-redux/index.d.ts
+// export function useSelector<TState, TSelected>(
+//   selector: (state: TState) => TSelected,
+//   equalityFn?: (left: TSelected, right: TSelected) => boolean
+// ): TSelected;
+// =============
+// `a.default is not a function`
+// // https://github.com/FormidableLabs/react-fast-compare/pulls/62
+// Test usage of this module elsewhere? Or push a release and hope the upstream is fixed?

test/typescript/index.ts

@@ -0,0 +1,43 @@
+import React from "react";
+
+const equal = require("../..");
+
+type DeepObject = {
+  any: any;
+};
+
+type State = {
+  any: {
+    any: any;
+  };
+};
+
+// State
+const selector = (state: State) => {
+  a: {
+    b: [1, 2, 3];
+  }
+};
+
+class TestComponent extends React.Component {
+  constructor() {
+    super();
+    this.useSelector = this.useSelector;
+  }
+
+  shouldComponentUpdate(nextProps) {
+    return !equal(this.props, nextProps);
+  }
+
+  useSelector<TState, TSelected>(
+    selector: (state: TState) => TSelected,
+    equalityFn?: (left: TSelected, right: TSelected) => boolean
+  ): TSelected;
+
+  this.useSelector(selector); // typed correctly as DeepObject
+  this.useSelector(selector, equal); // typed as any
+
+  render() {
+    // ...
+  }
+};