From 4b370a54d50ebdd48b0e3350c5b786dfddf029fb Mon Sep 17 00:00:00 2001
From: Steve Workman <steve.workman@maersk.com>
Date: Mon, 4 Mar 2019 11:33:24 +0000
Subject: [PATCH] feat(cli): Added makeJSOnlyValue to generator API. Provides
 convenience method for passing JS into config files. Issue #3535

---
 docs/dev-guide/generator-api.md               |  8 ++++++++
 packages/@vue/cli/__tests__/Generator.spec.js | 20 +++++++++++++++++++
 packages/@vue/cli/lib/GeneratorAPI.js         | 10 ++++++++++
 3 files changed, 38 insertions(+)

diff --git a/docs/dev-guide/generator-api.md b/docs/dev-guide/generator-api.md
index c71e1a0355..889b44bba5 100644
--- a/docs/dev-guide/generator-api.md
+++ b/docs/dev-guide/generator-api.md
@@ -97,6 +97,14 @@ Add a message to be printed when the generator exits (after any other standard m
 - **Usage**:
 Convenience method for generating a JS config file from JSON
 
+## makeJSOnlyValue
+
+- **Arguments**
+  - `{any} str` - JS expression as a string
+
+- **Usage**:
+Turns a string expression into executable JS for .js config files
+
 ## injectImports
 
 - **Arguments**
diff --git a/packages/@vue/cli/__tests__/Generator.spec.js b/packages/@vue/cli/__tests__/Generator.spec.js
index 0bc823872f..3ae81ed220 100644
--- a/packages/@vue/cli/__tests__/Generator.spec.js
+++ b/packages/@vue/cli/__tests__/Generator.spec.js
@@ -656,3 +656,23 @@ test('extract config files', async () => {
   expect(fs.readFileSync('/jest.config.js', 'utf-8')).toMatch(js(configs.jest))
   expect(fs.readFileSync('/.browserslistrc', 'utf-8')).toMatch('> 1%\nnot <= IE8')
 })
+
+test('generate a JS-Only value from a string', async () => {
+  const jsAsString = 'true ? "alice" : "bob"'
+
+  const generator = new Generator('/', { plugins: [
+    {
+      id: 'test',
+      apply: api => {
+        api.extendPackage({
+          testScript: api.makeJSOnlyValue(jsAsString)
+        })
+      }
+    }
+  ] })
+
+  await generator.generate({})
+
+  expect(generator.pkg).toHaveProperty('testScript')
+  expect(typeof generator.pkg.testScript).toBe('function')
+})
diff --git a/packages/@vue/cli/lib/GeneratorAPI.js b/packages/@vue/cli/lib/GeneratorAPI.js
index 8a39bb4f06..35ca1a36bf 100644
--- a/packages/@vue/cli/lib/GeneratorAPI.js
+++ b/packages/@vue/cli/lib/GeneratorAPI.js
@@ -240,6 +240,16 @@ class GeneratorAPI {
     return `module.exports = ${stringifyJS(value, null, 2)}`
   }
 
+  /**
+   * Turns a string expression into executable JS for JS configs.
+   * @param {*} str JS expression as a string
+   */
+  makeJSOnlyValue (str) {
+    const fn = () => {}
+    fn.__expression = str
+    return fn
+  }
+
   /**
    * Add import statements to a file.
    */