add patch/unpatch utility methods

src/utils.ts

@@ -125,3 +125,54 @@ export function shallowEqual(objA, objB) {
   }
   return true;
 }
+
+export function patch(C: any, patchName: string, patch: any) {
+  const proto = C.prototype;
+  if (!proto.__patches) {
+    proto.__patches = {
+      origMethods: {},
+      patches: {},
+      current: []
+    };
+  }
+  if (proto.__patches.patches[patchName]) {
+    throw new Error(`Patch [${patchName}] already exists`);
+  }
+  proto.__patches.patches[patchName] = patch;
+  applyPatch(proto, patch);
+  proto.__patches.current.push(patchName);
+
+  function applyPatch(proto, patch) {
+    Object.keys(patch).forEach(function(methodName) {
+      const method = patch[methodName];
+      if (typeof method === "function") {
+        const original = proto[methodName];
+        if (!(methodName in proto.__patches.origMethods)) {
+          proto.__patches.origMethods[methodName] = original;
+        }
+        proto[methodName] = function(...args) {
+          this._super = original;
+          return method.call(this, ...args);
+        };
+      }
+    });
+  }
+}
+
+export function unpatch(C: any, patchName: string) {
+  const proto = C.prototype;
+  const patchInfo = proto.__patches;
+  delete proto.__patches;
+
+  // reset to original
+  for (let k in patchInfo.origMethods) {
+    proto[k] = patchInfo.origMethods[k];
+  }
+
+  // apply other patches
+  for (let name of patchInfo.current) {
+    if (name !== patchName) {
+      patch(C, name, patchInfo.patches[name]);
+    }
+  }
+}

tests/utils.test.ts

@@ -5,7 +5,9 @@ import {
   memoize,
   debounce,
   findInTree,
-  shallowEqual
+  shallowEqual,
+  patch,
+  unpatch
 } from "../src/utils";
 
 describe("escape", () => {
@@ -103,3 +105,56 @@ describe("shallowEqual", () => {
     expect(shallowEqual({ a: 1 }, ["a"])).toBe(false);
   });
 });
+
+describe("patch/unpatch", () => {
+  test("can monkey patch a class", () => {
+    class Test {
+      n = 1;
+
+      doSomething(): string {
+        return "hey";
+      }
+    }
+
+    patch(Test, "some_custo", {
+      doSomething(): string {
+        this.n = this.n + 1;
+        return this._super();
+      }
+    });
+
+    const t = new Test();
+    expect(t.n).toBe(1);
+    expect(t.doSomething()).toBe("hey");
+    expect(t.n).toBe(2);
+  });
+
+  test("cannot patch a class twice with same patch name", () => {
+    class Test {}
+
+    patch(Test, "some_custo", {});
+    expect(() => {
+      patch(Test, "some_custo", {});
+    }).toThrow();
+  });
+
+  test("can unpatch a class", () => {
+    class Test {
+      doSomething(): number {
+        return 1;
+      }
+    }
+
+    patch(Test, "some_custo", {
+      doSomething(): number {
+        return this._super() + 2;
+      }
+    });
+
+    const t = new Test();
+    expect(t.doSomething()).toBe(3);
+
+    unpatch(Test, "some_custo");
+    expect(t.doSomething()).toBe(1);
+  });
+});