Enable the unicorn/prefer-class-fields ESLint plugin rule

This leads to slightly shorter code[1] when initializing classes, and in some cases we can even remove the constructors, which shouldn't hurt; see https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/docs/rules/prefer-class-fields.md

It's probably possible to also change a lot of these class fields to private ones[2], however it's often difficult to tell at a glance if that's safe hence this patch only does this for the `PDFRenderingQueue`.

---

[1] This reduces the size of the `gulp mozcentral` output by 999 bytes, for a mostly mechanical code change.

[2] That sort of re-factoring should generally be done separately, on a class-by-class basis, to reduce the risk of regressions.

Author: Snuffleupagus

eslint.config.mjs

@@ -148,6 +148,7 @@ export default [
       "unicorn/prefer-array-index-of": "error",
       "unicorn/prefer-array-some": "error",
       "unicorn/prefer-at": "error",
+      "unicorn/prefer-class-fields": "error",
       "unicorn/prefer-classlist-toggle": "error",
       "unicorn/prefer-date-now": "error",
       "unicorn/prefer-dom-node-append": "error",

src/core/annotation.js

@@ -1462,14 +1462,17 @@ class Annotation {
  * Contains all data regarding an annotation's border style.
  */
 class AnnotationBorderStyle {
-  constructor() {
-    this.width = 1;
-    this.rawWidth = 1;
-    this.style = AnnotationBorderStyleType.SOLID;
-    this.dashArray = [3];
-    this.horizontalCornerRadius = 0;
-    this.verticalCornerRadius = 0;
-  }
+  width = 1;
+
+  rawWidth = 1;
+
+  style = AnnotationBorderStyleType.SOLID;
+
+  dashArray = [3];
+
+  horizontalCornerRadius = 0;
+
+  verticalCornerRadius = 0;
 
   /**
    * Set the width.

src/core/cff_parser.js

@@ -991,24 +991,31 @@ class CFFParser {
 
 // Compact Font Format
 class CFF {
-  constructor() {
-    this.header = null;
-    this.names = [];
-    this.topDict = null;
-    this.strings = new CFFStrings();
-    this.globalSubrIndex = null;
-
-    // The following could really be per font, but since we only have one font
-    // store them here.
-    this.encoding = null;
-    this.charset = null;
-    this.charStrings = null;
-    this.fdArray = [];
-    this.fdSelect = null;
-
-    this.isCIDFont = false;
-    this.charStringCount = 0;
-  }
+  header = null;
+
+  names = [];
+
+  topDict = null;
+
+  strings = new CFFStrings();
+
+  globalSubrIndex = null;
+
+  // The following could really be per font, but since we only have one font
+  // store them here.
+  encoding = null;
+
+  charset = null;
+
+  charStrings = null;
+
+  fdArray = [];
+
+  fdSelect = null;
+
+  isCIDFont = false;
+
+  charStringCount = 0;
 
   duplicateFirstGlyph() {
     // Browsers will not display a glyph at position 0. Typically glyph 0 is

src/core/crypto.js

@@ -32,9 +32,11 @@ import { calculateSHA256 } from "./calculate_sha256.js";
 import { DecryptStream } from "./decrypt_stream.js";
 
 class ARCFourCipher {
+  a = 0;
+
+  b = 0;
+
   constructor(key) {
-    this.a = 0;
-    this.b = 0;
     const s = new Uint8Array(256);
     const keyLength = key.length;
 

src/core/editor/pdf_editor.js

@@ -74,33 +74,52 @@ class XRefWrapper {
 }
 
 class PDFEditor {
+  hasSingleFile = false;
+
+  currentDocument = null;
+
+  oldPages = [];
+
+  newPages = [];
+
+  xref = [null];
+
+  xrefWrapper = new XRefWrapper(this.xref);
+
+  newRefCount = 1;
+
+  namesDict = null;
+
+  version = "1.7";
+
+  pageLabels = null;
+
+  namedDestinations = new Map();
+
+  parentTree = new Map();
+
+  structTreeKids = [];
+
+  idTree = new Map();
+
+  classMap = new Dict();
+
+  roleMap = new Dict();
+
+  namespaces = new Map();
+
+  structTreeAF = [];
+
+  structTreePronunciationLexicon = [];
+
   constructor({ useObjectStreams = true, title = "", author = "" } = {}) {
-    this.hasSingleFile = false;
-    this.currentDocument = null;
-    this.oldPages = [];
-    this.newPages = [];
-    this.xref = [null];
-    this.xrefWrapper = new XRefWrapper(this.xref);
-    this.newRefCount = 1;
     [this.rootRef, this.rootDict] = this.newDict;
     [this.infoRef, this.infoDict] = this.newDict;
     [this.pagesRef, this.pagesDict] = this.newDict;
-    this.namesDict = null;
     this.useObjectStreams = useObjectStreams;
     this.objStreamRefs = useObjectStreams ? new Set() : null;
-    this.version = "1.7";
     this.title = title;
     this.author = author;
-    this.pageLabels = null;
-    this.namedDestinations = new Map();
-    this.parentTree = new Map();
-    this.structTreeKids = [];
-    this.idTree = new Map();
-    this.classMap = new Dict();
-    this.roleMap = new Dict();
-    this.namespaces = new Map();
-    this.structTreeAF = [];
-    this.structTreePronunciationLexicon = [];
   }
 
   /**

src/core/type1_parser.js

@@ -79,13 +79,15 @@ const COMMAND_MAP = {
  *  the charStrings.
  */
 class Type1CharString {
-  constructor() {
-    this.width = 0;
-    this.lsb = 0;
-    this.flexing = false;
-    this.output = [];
-    this.stack = [];
-  }
+  width = 0;
+
+  lsb = 0;
+
+  flexing = false;
+
+  output = [];
+
+  stack = [];
 
   convert(encoded, subrs, seacAnalysisEnabled) {
     const count = encoded.length;

src/display/annotation_storage.js

@@ -35,15 +35,17 @@ class AnnotationStorage {
 
   #storage = new Map();
 
-  constructor() {
-    // Callbacks to signal when the modification state is set or reset.
-    // This is used by the viewer to only bind on `beforeunload` if forms
-    // are actually edited to prevent doing so unconditionally since that
-    // can have undesirable effects.
-    this.onSetModified = null;
-    this.onResetModified = null;
-    this.onAnnotationEditor = null;
+  // Callbacks to signal when the modification state is set or reset.
+  // This is used by the viewer to only bind on `beforeunload` if forms
+  // are actually edited to prevent doing so unconditionally since that
+  // can have undesirable effects.
+  onSetModified = null;
+
+  onResetModified = null;
 
+  onAnnotationEditor = null;
+
+  constructor() {
     if (typeof PDFJSDev === "undefined" || PDFJSDev.test("TESTING")) {
       // For testing purposes.
       Object.defineProperty(this, "_setValues", {