feat(typescript): add convertJsToTs and allowJs options (#4212)

Close #2676

At the moment when we run `vue add`, Vue CLI renames all `*.js` files to `*.ts`. This PR introduces two new prompts on `@vue/cli-plugin-typescript` late-invokation:

1. `convertJsToTs`: if set to `true`, renames all `.js` files to `.ts`. Otherwise renames only `main.js` -> `main.ts`;
2. `allowJs`: if set to `true`, adds `allowJs: true` to TSConfig compiler options.

(cherry picked from commit 38debb4)

Author: NataliaTepluhina

packages/@vue/cli-plugin-typescript/generator/convert.js

@@ -1,22 +1,33 @@
-module.exports = (api, { tsLint = false } = {}) => {
-  // delete all js files that have a ts file of the same name
-  // and simply rename other js files to ts
+module.exports = (api, { tsLint = false, convertAllFiles = true } = {}) => {
   const jsRE = /\.js$/
   const excludeRE = /^tests\/e2e\/|(\.config|rc)\.js$/
   const convertLintFlags = require('../lib/convertLintFlags')
   api.postProcessFiles(files => {
-    for (const file in files) {
-      if (jsRE.test(file) && !excludeRE.test(file)) {
-        const tsFile = file.replace(jsRE, '.ts')
-        if (!files[tsFile]) {
-          let content = files[file]
-          if (tsLint) {
-            content = convertLintFlags(content)
+    if (convertAllFiles) {
+      // delete all js files that have a ts file of the same name
+      // and simply rename other js files to ts
+      for (const file in files) {
+        if (jsRE.test(file) && !excludeRE.test(file)) {
+          const tsFile = file.replace(jsRE, '.ts')
+          if (!files[tsFile]) {
+            let content = files[file]
+            if (tsLint) {
+              content = convertLintFlags(content)
+            }
+            files[tsFile] = content
           }
-          files[tsFile] = content
+          delete files[file]
         }
-        delete files[file]
       }
+    } else {
+      // rename only main file to main.ts
+      const tsFile = api.entryFile.replace(jsRE, '.ts')
+      let content = files[api.entryFile]
+      if (tsLint) {
+        content = convertLintFlags(content)
+      }
+      files[tsFile] = content
+      delete files[api.entryFile]
     }
   })
 }

packages/@vue/cli-plugin-typescript/generator/index.js

@@ -1,7 +1,9 @@
 module.exports = (api, {
   classComponent,
   tsLint,
-  lintOn = []
+  lintOn = [],
+  convertJsToTs,
+  allowJs
 }, _, invoking) => {
   if (typeof lintOn === 'string') {
     lintOn = lintOn.split(',')
@@ -82,5 +84,5 @@ module.exports = (api, {
     hasJest: api.hasPlugin('unit-jest')
   })
 
-  require('./convert')(api, { tsLint })
+  require('./convert')(api, { tsLint, convertJsToTs })
 }

packages/@vue/cli-plugin-typescript/generator/template/tsconfig.json

@@ -9,6 +9,9 @@
     <%_ if (options.classComponent) { _%>
     "experimentalDecorators": true,
     <%_ } _%>
+    <%_ if (options.allowJs) { _%>
+    "allowJs": true,
+    <%_ } _%>
     "esModuleInterop": true,
     "allowSyntheticDefaultImports": true,
     "sourceMap": true,

packages/@vue/cli-plugin-typescript/prompts.js

@@ -36,6 +36,18 @@ const prompts = module.exports = [
         value: 'commit'
       }
     ]
+  },
+  {
+    name: `convertJsToTs`,
+    type: `confirm`,
+    message: `Convert all .js files to .ts?`,
+    default: true
+  },
+  {
+    name: `allowJs`,
+    type: `confirm`,
+    message: `Allow .js files to be compiled?`,
+    default: false
   }
 ]