Add ExtensibleFunction class (#32)

superset-frontend/temporary_superset_ui/superset-ui/packages/superset-ui-core/src/index.js

@@ -1,3 +1,4 @@
+export { default as ExtensibleFunction } from './models/ExtensibleFunction';
 export { default as Plugin } from './models/Plugin';
 export { default as Preset } from './models/Preset';
 export { default as Registry } from './models/Registry';

superset-frontend/temporary_superset_ui/superset-ui/packages/superset-ui-core/src/models/ExtensibleFunction.js

@@ -0,0 +1,9 @@
+/**
+ * From https://stackoverflow.com/questions/36871299/how-to-extend-function-with-es6-classes
+ */
+
+export default class ExtensibleFunction extends Function {
+  constructor(fn) {
+    return Object.setPrototypeOf(fn, new.target.prototype);
+  }
+}

superset-frontend/temporary_superset_ui/superset-ui/packages/superset-ui-core/test/index.test.js

@@ -1,4 +1,5 @@
 import {
+  ExtensibleFunction,
   Plugin,
   Preset,
   Registry,
@@ -12,6 +13,7 @@ import {
 describe('index', () => {
   it('exports modules', () => {
     [
+      ExtensibleFunction,
       Plugin,
       Preset,
       Registry,

superset-frontend/temporary_superset_ui/superset-ui/packages/superset-ui-core/test/models/ExtensibleFunction.test.js

@@ -0,0 +1,52 @@
+import ExtensibleFunction from '../../src/models/ExtensibleFunction';
+
+describe('ExtensibleFunction', () => {
+  class Func1 extends ExtensibleFunction {
+    constructor(x) {
+      super(() => x); // closure
+    }
+  }
+  class Func2 extends ExtensibleFunction {
+    constructor(x) {
+      super(() => this.x); // arrow function, refer to its own field
+      this.x = x;
+    }
+
+    hi() {
+      return 'hi';
+    }
+  }
+  class Func3 extends ExtensibleFunction {
+    constructor(x) {
+      super(function customName() {
+        return customName.x;
+      }); // named function
+      this.x = x;
+    }
+  }
+
+  it('its subclass is an instance of Function', () => {
+    expect(Func1).toBeInstanceOf(Function);
+    expect(Func2).toBeInstanceOf(Function);
+    expect(Func3).toBeInstanceOf(Function);
+  });
+
+  const func1 = new Func1(100);
+  const func2 = new Func2(100);
+  const func3 = new Func3(100);
+
+  it('an instance of its subclass is executable like regular function', () => {
+    expect(func1()).toEqual(100);
+    expect(func2()).toEqual(100);
+    expect(func3()).toEqual(100);
+  });
+
+  it('its subclass behaves like regular class with its own fields and functions', () => {
+    expect(func2.x).toEqual(100);
+    expect(func2.hi()).toEqual('hi');
+  });
+
+  it('its subclass can set name by passing named function to its constructor', () => {
+    expect(func3.name).toEqual('customName');
+  });
+});