stage 10

jacekkopecky · jacekkopecky · commit f9780dfcb9f0 · 2020-03-26T16:56:32.000Z
diff --git a/stages/classes.mjs b/stages/classes.mjs
@@ -4,6 +4,11 @@ export class Shape {
     this.y = y;
     this.col = col;
   }
+
+  moveBy(x, y) {
+    this.x += x;
+    this.y += y;
+  }
 }
 
 export class Rectangle extends Shape {
diff --git a/stages/index.js b/stages/index.js
@@ -1,7 +1,10 @@
 'use strict';
 /**
- * We use an array instead of four variables,
- * resulting in cleaner code.
+ * Adding functions to a superclass makes them available
+ * to all classes that extend it.
+ *
+ * Here, we use `moveBy()` on rectangles and circles
+ * even though it is only defined on Shape.
  */
 
 import { Circle, Rectangle } from './classes.mjs';
@@ -19,4 +22,6 @@ const ctx = document.querySelector('canvas').getContext('2d');
 
 for (const s of shapes) {
   s.draw(ctx);
+  s.moveBy(110, 30);
+  s.draw(ctx);
 }

Original file line number	Diff line number	Diff line change
`@@ -4,6 +4,11 @@ export class Shape {`
`4`	`4`	`this.y = y;`
`5`	`5`	`this.col = col;`
`6`	`6`	`}`
	`7`	`+`
	`8`	`+ moveBy(x, y) {`
	`9`	`+ this.x += x;`
	`10`	`+ this.y += y;`
	`11`	`+ }`
`7`	`12`	`}`
`8`	`13`
`9`	`14`	`export class Rectangle extends Shape {`