Fixes #19 - Allows transforming a title instead of just skipping it

README.md

@@ -135,6 +135,7 @@ The plugin takes three options, `toTitle` (required), `ifTitleFound` (optional),
 
 - `ifTitleFound` is an optional string value that may either be set to:
   -  `'skip'` - skips adding a title if it has already been manually specified in the code
+  -  `'transform'` - replaces the existing title with the value from `toTitle`
   -  `undefined` (or any other value) - raise an error if processing a file that already defines a title
 
 - `renameDefaultExportsTo` is an optional string value that controls scenario 3 as described above. It is `undefined` by default.

src/__tests__/index.js

@@ -143,4 +143,37 @@ tester({
   babelOptions: {
     plugins: ["@babel/plugin-syntax-jsx"],
   }
+});
+
+tester({
+  plugin,
+  tests: [
+      {
+          title: "Default export object with title and ifTitleFound: transform",
+          code: outdent`
+            import React from 'react';
+            import { Component } from './index';
+            export default {
+              title: "existing"
+            };
+            export const Default = () => <Component />;
+          `,
+          output: outdent`
+            import React from 'react';
+            import { Component } from './index';
+            export default {
+              title: "existingbar"
+            };
+            export const Default = () => <Component />;
+          `
+      }
+  ],
+  pluginOptions: {
+    title: 'bar',
+    toTitle: (state) => state.title + state.opts.title,
+    ifTitleFound: 'transform'
+  },
+  babelOptions: {
+    plugins: ["@babel/plugin-syntax-jsx"],
+  }
 });

src/index.js

@@ -1,14 +1,17 @@
 const TITLE_KEY = 'title';
 
-const fixObjectDefaultExport = (path, t, title, ifTitleFound) => {
+const fixObjectDefaultExport = (path, t, title, ifTitleFound, titlePropertyIndex) => {
     if (path.node.declaration.properties) {
-        const titleProperty = path.node.declaration.properties.find(node =>
-            node.key && node.key.name === TITLE_KEY
-        );
-        if (titleProperty) {
+        const newTitleNode = t.objectProperty(t.identifier(TITLE_KEY), t.stringLiteral(title))
+        if (titlePropertyIndex !== -1) {
             switch (ifTitleFound) {
                 case 'skip':
                     return;
+                case 'transform':
+                    const newNode = t.cloneNode(path.node);
+                    newNode.declaration.properties.splice(titlePropertyIndex, 1, newTitleNode);
+                    path.replaceWith(newNode);
+                    return;
                 default:
                     throw new Error(
                         `Default export object has a '${TITLE_KEY}' property; the title should, however, be generated. Please remove '${TITLE_KEY}'.`
@@ -17,7 +20,7 @@ const fixObjectDefaultExport = (path, t, title, ifTitleFound) => {
         }
         path.get('declaration').pushContainer(
             'properties', 
-            t.objectProperty(t.identifier(TITLE_KEY), t.stringLiteral(title))
+            newTitleNode
         );
     } else {
         throw new Error('Default export object does not have properties.');
@@ -61,6 +64,21 @@ const plugin = babel => {
                     return;
                 }
                 state.defaultExportPath = path;
+                state.titleIndex = -1;
+                state.title = '';
+
+                const properties = path.node.declaration.properties;
+                if (properties) {
+                    const titlePropertyIndex = properties.findIndex(node =>
+                        node.key && node.key.name === TITLE_KEY
+                    );
+                    if (titlePropertyIndex !== -1) {
+                        if (properties[titlePropertyIndex].value.type === 'StringLiteral') {
+                            state.title = properties[titlePropertyIndex].value.value;
+                            state.titleIndex = titlePropertyIndex;
+                        }
+                    }
+                }
             },
             ExportNamedDeclaration: (path, state) => {
                 if (state.handled) {
@@ -93,7 +111,7 @@ const plugin = babel => {
 
                     if (state.defaultExportPath) {
                         if (state.defaultExportPath.node.declaration.type === 'ObjectExpression') {
-                            fixObjectDefaultExport(state.defaultExportPath, t, title, state.opts.ifTitleFound);
+                            fixObjectDefaultExport(state.defaultExportPath, t, title, state.opts.ifTitleFound, state.titleIndex);
                         } else {
                             if (renameDefaultExportsTo) {
                                 if (!state.namedDefaultExportPath) {