mark elements params as readonly & remove unnecessary copying

src/scene/comparisons.ts

@@ -2,7 +2,7 @@ import { ExcalidrawElement } from "../element/types";
 import { hitTest } from "../element/collision";
 import { getElementAbsoluteCoords } from "../element";
 
-export const hasBackground = (elements: ExcalidrawElement[]) =>
+export const hasBackground = (elements: readonly ExcalidrawElement[]) =>
   elements.some(
     element =>
       element.isSelected &&
@@ -11,7 +11,7 @@ export const hasBackground = (elements: ExcalidrawElement[]) =>
         element.type === "diamond")
   );
 
-export const hasStroke = (elements: ExcalidrawElement[]) =>
+export const hasStroke = (elements: readonly ExcalidrawElement[]) =>
   elements.some(
     element =>
       element.isSelected &&
@@ -21,11 +21,11 @@ export const hasStroke = (elements: ExcalidrawElement[]) =>
         element.type === "arrow")
   );
 
-export const hasText = (elements: ExcalidrawElement[]) =>
+export const hasText = (elements: readonly ExcalidrawElement[]) =>
   elements.some(element => element.isSelected && element.type === "text");
 
 export function getElementAtPosition(
-  elements: ExcalidrawElement[],
+  elements: readonly ExcalidrawElement[],
   x: number,
   y: number
 ) {
@@ -42,7 +42,7 @@ export function getElementAtPosition(
 }
 
 export function getElementContainingPosition(
-  elements: ExcalidrawElement[],
+  elements: readonly ExcalidrawElement[],
   x: number,
   y: number
 ) {

src/scene/createScene.ts

@@ -1,6 +1,6 @@
 import { ExcalidrawElement } from "../element/types";
 
 export const createScene = () => {
-  const elements = Array.of<ExcalidrawElement>();
+  const elements: readonly ExcalidrawElement[] = [];
   return { elements };
 };

src/scene/data.ts

@@ -23,11 +23,14 @@ function saveFile(name: string, data: string) {
 }
 
 interface DataState {
-  elements: ExcalidrawElement[];
+  elements: readonly ExcalidrawElement[];
   appState: any;
 }
 
-export function saveAsJSON(elements: ExcalidrawElement[], name: string) {
+export function saveAsJSON(
+  elements: readonly ExcalidrawElement[],
+  name: string
+) {
   const serialized = JSON.stringify({
     version: 1,
     source: window.location.origin,
@@ -74,7 +77,7 @@ export function loadFromJSON() {
 }
 
 export function exportAsPNG(
-  elements: ExcalidrawElement[],
+  elements: readonly ExcalidrawElement[],
   canvas: HTMLCanvasElement,
   {
     exportBackground,
@@ -140,7 +143,7 @@ export function exportAsPNG(
 }
 
 function restore(
-  savedElements: ExcalidrawElement[],
+  savedElements: readonly ExcalidrawElement[],
   savedState: any
 ): DataState {
   return {
@@ -185,7 +188,7 @@ export function restoreFromLocalStorage() {
 }
 
 export function saveToLocalStorage(
-  elements: ExcalidrawElement[],
+  elements: readonly ExcalidrawElement[],
   state: AppState
 ) {
   localStorage.setItem(LOCAL_STORAGE_KEY, JSON.stringify(elements));

src/scene/scrollbars.ts

@@ -7,7 +7,7 @@ export const SCROLLBAR_WIDTH = 6;
 export const SCROLLBAR_COLOR = "rgba(0,0,0,0.3)";
 
 export function getScrollBars(
-  elements: ExcalidrawElement[],
+  elements: readonly ExcalidrawElement[],
   canvasWidth: number,
   canvasHeight: number,
   scrollX: number,
@@ -76,7 +76,7 @@ export function getScrollBars(
 }
 
 export function isOverScrollBars(
-  elements: ExcalidrawElement[],
+  elements: readonly ExcalidrawElement[],
   x: number,
   y: number,
   canvasWidth: number,

src/scene/selection.ts

@@ -2,7 +2,7 @@ import { ExcalidrawElement } from "../element/types";
 import { getElementAbsoluteCoords } from "../element";
 
 export function setSelection(
-  elements: ExcalidrawElement[],
+  elements: readonly ExcalidrawElement[],
   selection: ExcalidrawElement
 ) {
   const [
@@ -29,7 +29,7 @@ export function setSelection(
   return elements;
 }
 
-export function clearSelection(elements: ExcalidrawElement[]) {
+export function clearSelection(elements: readonly ExcalidrawElement[]) {
   elements.forEach(element => {
     element.isSelected = false;
   });
@@ -37,11 +37,11 @@ export function clearSelection(elements: ExcalidrawElement[]) {
   return elements;
 }
 
-export function deleteSelectedElements(elements: ExcalidrawElement[]) {
+export function deleteSelectedElements(elements: readonly ExcalidrawElement[]) {
   return elements.filter(el => !el.isSelected);
 }
 
-export function getSelectedIndices(elements: ExcalidrawElement[]) {
+export function getSelectedIndices(elements: readonly ExcalidrawElement[]) {
   const selectedIndices: number[] = [];
   elements.forEach((element, index) => {
     if (element.isSelected) {
@@ -51,11 +51,11 @@ export function getSelectedIndices(elements: ExcalidrawElement[]) {
   return selectedIndices;
 }
 
-export const someElementIsSelected = (elements: ExcalidrawElement[]) =>
+export const someElementIsSelected = (elements: readonly ExcalidrawElement[]) =>
   elements.some(element => element.isSelected);
 
 export function getSelectedAttribute<T>(
-  elements: ExcalidrawElement[],
+  elements: readonly ExcalidrawElement[],
   getAttribute: (element: ExcalidrawElement) => T
 ): T | null {
   const attributes = Array.from(