Optimize parallax

src/framework/helper.ts

@@ -10,3 +10,17 @@ export const randomFactory = seed => () =>
   ((2 ** 31 - 1) & (seed = Math.imul(48271, seed))) / 2 ** 31;
 
 export const fixedSeedRandom = randomFactory(42);
+
+export const choose = <T>(
+  list: Array<T>,
+  random: () => number = fixedSeedRandom
+): T => list[randomInInterval(0, list.length, random)];
+
+export const randomInInterval = (
+  aClosed: number,
+  bOpen: number,
+  random: () => number = fixedSeedRandom
+): number => Math.floor((bOpen - aClosed) * random()) + aClosed;
+
+export const sum = (list: ArrayLike<number>): number =>
+  Array.prototype.reduce.call(list, (a, sum) => a + sum, 0);

src/framework/page-element.ts

@@ -9,6 +9,7 @@ export abstract class PageElement {
   }
 
   protected setElement(value: HTMLElement) {
+    this.getElement()?.parentElement?.replaceChild(value, this.getElement());
     this.element = value;
   }
 

src/framework/page.ts

@@ -12,7 +12,7 @@ export class Page extends PageElement {
       { type: PageEventType.eventGeneratorChanged, data: this },
       this
     );
-    rootElement.append(...children.map(e => e.getElement()));
+    rootElement.append(...children.map(e => e.getElement()).filter(e => e));
     this.giveEvent({ type: PageEventType.onLoad }, this);
   }
 }