Added NextScript component (#101)

* Added NextScriptDeferred component that allows you to import scripts with defer instead of async in _document.js.

* Add mode

* add missing files

package.json

@@ -1,6 +1,6 @@
 {
   "name": "react-storefront",
-  "version": "8.7.3",
+  "version": "8.8.0",
   "description": "Build and deploy e-commerce progressive web apps (PWAs) in record time.",
   "module": "./index.js",
   "license": "Apache-2.0",

src/NextScript.js

@@ -0,0 +1,30 @@
+import React from 'react'
+import { NextScript as OriginalNextScript } from 'next/document'
+import PropTypes from 'prop-types'
+
+/**
+ * A replacement for NextScript from `next/document` that gives you greater control over how script elements are rendered.
+ * This should be used in the body of `pages/_document.js` in place of `NextScript`.
+ */
+export default class NextScript extends OriginalNextScript {
+  static propTypes = {
+    /**
+     * Set to `defer` to use `defer` instead of `async` when rendering script elements.
+     */
+    mode: PropTypes.oneOf(['async', 'defer']),
+  }
+
+  static defaultProps = {
+    mode: 'async',
+  }
+
+  getScripts() {
+    return super.getScripts().map(script => {
+      return React.cloneElement(script, {
+        key: script.props.src,
+        defer: this.props.mode === 'defer' ? true : undefined,
+        async: this.props.mode === 'async' ? true : undefined,
+      })
+    })
+  }
+}

test/NextScript.test.js

@@ -0,0 +1,38 @@
+import React, { Component } from 'react'
+import { mount } from 'enzyme'
+
+describe('NextScriptDeferred', () => {
+  let NextScript
+
+  beforeEach(() => {
+    jest.isolateModules(() => {
+      jest.doMock('next/document', () => ({
+        NextScript: class OriginalNextScript extends Component {
+          getScripts() {
+            return [<script src="foo.js" async />]
+          }
+
+          render() {
+            return <>{this.getScripts()}</>
+          }
+        },
+      }))
+
+      NextScript = require('react-storefront/NextScript').default
+    })
+  })
+
+  it('should remove async and add defer to all script tags returned from super.getScripts', () => {
+    const wrapper = mount(<NextScript mode="defer" />)
+    const scriptProps = wrapper.find('script').props()
+    expect(scriptProps.async).toBe(undefined)
+    expect(scriptProps.defer).toBe(true)
+  })
+
+  it('should use async by default', () => {
+    const wrapper = mount(<NextScript />)
+    const scriptProps = wrapper.find('script').props()
+    expect(scriptProps.async).toBe(true)
+    expect(scriptProps.defer).toBe(undefined)
+  })
+})