style: enable eslint rule prefer-const

.eslintrc.js

@@ -21,7 +21,6 @@ module.exports = {
     'no-unneeded-ternary': 'off',
     'no-unused-expressions': 'off',
     'no-unused-vars': 'off',
-    'prefer-const': 'off',
     eqeqeq: 'off',
     semi: 'off'
   }

src/h.ts

@@ -10,7 +10,7 @@ function addNS (data: any, children: VNodes | undefined, sel: string | undefined
   data.ns = 'http://www.w3.org/2000/svg';
   if (sel !== 'foreignObject' && children !== undefined) {
     for (let i = 0; i < children.length; ++i) {
-      let childData = children[i].data;
+      const childData = children[i].data;
       if (childData !== undefined) {
         addNS(childData, (children[i] as VNode).children as VNodes, children[i].sel);
       }

src/modules/dataset.ts

@@ -6,7 +6,7 @@ export type Dataset = Record<string, string>;
 const CAPS_REGEX = /[A-Z]/g;
 
 function updateDataset (oldVnode: VNode, vnode: VNode): void {
-  let elm: HTMLElement = vnode.elm as HTMLElement;
+  const elm: HTMLElement = vnode.elm as HTMLElement;
   let oldDataset = (oldVnode.data as VNodeData).dataset;
   let dataset = (vnode.data as VNodeData).dataset;
   let key: string;

src/modules/style.ts

@@ -46,7 +46,7 @@ function updateStyle (oldVnode: VNode, vnode: VNode): void {
   for (name in style) {
     cur = style[name];
     if (name === 'delayed' && style.delayed) {
-      for (let name2 in style.delayed) {
+      for (const name2 in style.delayed) {
         cur = style.delayed[name2];
         if (!oldHasDel || cur !== (oldStyle.delayed as any)[name2]) {
           setNextFrame((elm as any).style, name2, cur);

src/snabbdom.ts

@@ -52,7 +52,7 @@ export { thunk } from './thunk';
 export function init (modules: Array<Partial<Module>>, domApi?: DOMAPI) {
   let i: number;
   let j: number;
-  let cbs = ({} as ModuleHooks);
+  const cbs = ({} as ModuleHooks);
 
   const api: DOMAPI = domApi !== undefined ? domApi : htmlDomApi;
 
@@ -91,8 +91,8 @@ export function init (modules: Array<Partial<Module>>, domApi?: DOMAPI) {
         data = vnode.data;
       }
     }
-    let children = vnode.children;
-    let sel = vnode.sel;
+    const children = vnode.children;
+    const sel = vnode.sel;
     if (sel === '!') {
       if (isUndef(vnode.text)) {
         vnode.text = '';
@@ -173,7 +173,7 @@ export function init (modules: Array<Partial<Module>>, domApi?: DOMAPI) {
     for (; startIdx <= endIdx; ++startIdx) {
       let listeners: number;
       let rm: () => void;
-      let ch = vnodes[startIdx];
+      const ch = vnodes[startIdx];
       if (ch != null) {
         if (isDef(ch.sel)) {
           invokeDestroyHook(ch);
@@ -271,8 +271,8 @@ export function init (modules: Array<Partial<Module>>, domApi?: DOMAPI) {
     const hook = vnode.data?.hook;
     hook?.prepatch?.(oldVnode, vnode);
     const elm = vnode.elm = oldVnode.elm!;
-    let oldCh = oldVnode.children as VNode[];
-    let ch = vnode.children as VNode[];
+    const oldCh = oldVnode.children as VNode[];
+    const ch = vnode.children as VNode[];
     if (oldVnode === vnode) return;
     if (vnode.data !== undefined) {
       for (let i = 0; i < cbs.update.length; ++i) cbs.update[i](oldVnode, vnode);

src/thunk.ts

@@ -33,8 +33,8 @@ function init (thunk: VNode): void {
 
 function prepatch (oldVnode: VNode, thunk: VNode): void {
   let i: number;
-  let old = oldVnode.data as VNodeData;
-  let cur = thunk.data as VNodeData;
+  const old = oldVnode.data as VNodeData;
+  const cur = thunk.data as VNodeData;
   const oldArgs = old.args;
   const args = cur.args;
   if (old.fn !== cur.fn || (oldArgs as any).length !== (args as any).length) {

src/vnode.ts

@@ -41,7 +41,7 @@ export function vnode (sel: string | undefined,
   children: Array<VNode | string> | undefined,
   text: string | undefined,
   elm: Element | Text | undefined): VNode {
-  let key = data === undefined ? undefined : data.key;
+  const key = data === undefined ? undefined : data.key;
   return { sel, data, children, text, elm, key };
 }