Use new eslint-plugin-functional instead of tslint-immutable

src/file/numbering/abstract-numbering.ts

@@ -32,7 +32,7 @@ class AbstractNumberingAttributes extends XmlAttributeComponent<{
 export class AbstractNumbering extends XmlComponent {
     public readonly id: number;
 
-    public constructor(id: number, levelOptions: ILevelsOptions[]) {
+    public constructor(id: number, levelOptions: readonly ILevelsOptions[]) {
         super("w:abstractNum");
         this.root.push(
             new AbstractNumberingAttributes({

src/file/numbering/level.spec.ts

@@ -2,8 +2,8 @@ import { expect } from "chai";
 
 import { Formatter } from "@export/formatter";
 
-import { Level, LevelFormat, LevelSuffix } from "./level";
 import { AlignmentType } from "..";
+import { Level, LevelFormat, LevelSuffix } from "./level";
 
 describe("Level", () => {
     describe("#constructor", () => {

src/file/numbering/level.ts

@@ -118,7 +118,7 @@ class Suffix extends XmlComponent {
 // http://officeopenxml.com/WPnumbering-isLgl.php
 // https://docs.microsoft.com/en-us/dotnet/api/documentformat.openxml.wordprocessing.islegalnumberingstyle?view=openxml-2.8.1
 class IsLegalNumberingStyle extends XmlComponent {
-    constructor() {
+    public constructor() {
         super("w:isLgl");
     }
 }

src/file/numbering/numbering.ts

@@ -10,8 +10,8 @@ import { ILevelsOptions, LevelFormat } from "./level";
 import { ConcreteNumbering } from "./num";
 
 export interface INumberingOptions {
-    readonly config: {
-        readonly levels: ILevelsOptions[];
+    readonly config: readonly {
+        readonly levels: readonly ILevelsOptions[];
         readonly reference: string;
     }[];
 }
@@ -203,33 +203,33 @@ export class Numbering extends XmlComponent {
             return;
         }
 
+        const referenceConfigLevels = this.referenceConfigMap.get(reference);
+        const firstLevelStartNumber = referenceConfigLevels && referenceConfigLevels[0].start;
+
         const concreteNumberingSettings = {
             numId: uniqueNumericId(),
             abstractNumId: abstractNumbering.id,
             reference,
             instance,
-            overrideLevel: {
-                num: 0,
-                start: 1,
-            },
+            overrideLevel:
+                firstLevelStartNumber && Number.isInteger(firstLevelStartNumber)
+                    ? {
+                          num: 0,
+                          start: firstLevelStartNumber,
+                      }
+                    : {
+                          num: 0,
+                          start: 1,
+                      },
         };
 
-        const referenceConfigLevels = this.referenceConfigMap.get(reference);
-        const firstLevelStartNumber = referenceConfigLevels && referenceConfigLevels[0].start;
-        if (firstLevelStartNumber && Number.isInteger(firstLevelStartNumber)) {
-            concreteNumberingSettings.overrideLevel = {
-                num: 0,
-                start: firstLevelStartNumber,
-            };
-        }
-
         this.concreteNumberingMap.set(fullReference, new ConcreteNumbering(concreteNumberingSettings));
     }
 
-    public get ConcreteNumbering(): ConcreteNumbering[] {
+    public get ConcreteNumbering(): readonly ConcreteNumbering[] {
         return Array.from(this.concreteNumberingMap.values());
     }
-    public get ReferenceConfig(): object[] {
+    public get ReferenceConfig(): readonly object[] {
         return Array.from(this.referenceConfigMap.values());
     }
 }