Merge pull request #1 from github/initial-implementation

Initial implementation

.eslintrc.json

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+{
+  "root": true,
+  "plugins": ["github"],
+  "extends": ["plugin:github/recommended", "plugin:github/typescript", "plugin:github/browser"],
+  "rules": {
+    "no-invalid-this": "off",
+    "@typescript-eslint/no-invalid-this": ["error"]
+  },
+  "overrides": [
+    {
+      "files": "test/*",
+      "rules": {
+        "github/unescaped-html-literal": "off"
+      },
+      "globals": {
+        "chai": false,
+        "expect": false
+      },
+      "env": {
+        "mocha": true
+      }
+    },
+    {
+      "files": "*.cjs",
+      "env": {
+        "node": true
+      }
+    }
+  ]
+}

.github/workflows/nodejs.yml

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+name: Build
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+
+jobs:
+  test-node:
+    name: Test on Node.js
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout the project
+      uses: actions/checkout@v2
+    - name: Cache node modules
+      uses: actions/cache@v2
+      with:
+        path: ~/.npm
+        key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}
+        restore-keys: |
+          ${{ runner.os }}-node-
+    - name: Use Node.js 14.7.0
+      uses: actions/setup-node@v1
+      with:
+        node-version: 14.7.0
+    - name: Install dependencies
+      run: npm i
+    - name: Run Node.js Tests
+      run: npm run test

.gitignore

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+node_modules
+*.tsbuildinfo
+lib/

CODEOWNERS

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+* @github/web-systems-reviewers

LICENSE

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+MIT License
+
+Copyright (c) 2020 GitHub, Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# Template Parts
+
+This library is designed as a "ponyfill" library that implements the design in the [Template Parts Proposal](https://github.com/domenic/template-parts) that has been sketched out in order to address [whatwg/html#2254](https://github.com/whatwg/html/issues/2254).
+
+This implements the minimally viable parts of the proposal, to provide something that works, but should be easy to drop if the Template Parts Proposal lands.
+
+To reiterate the example in the above proposal, given a template such as:
+
+```
+<template id="foo">
+  <div class="foo {{y}}">{{x}} world</div>
+</template>
+```
+
+We'd like `{{x}}` and `{{y}}` to be **template parts**, exposed as JavaScript objects which can be manipulated.
+
+With this library, and that given template, one could implement the following:
+
+```js
+import {StampedTemplate} from '@github/template-parts'
+
+const tpl = new StampedTemplate(document.getElementById('foo'), (parts, params) => {
+  for (const part of parts) {
+    const key = part.expression.trim()
+    const value = (key in params ? params[key] : '')
+    if (part.attribute) {
+      part.value = value
+    } else {
+      part.replaceWith(value)
+    }
+  }
+}, { x: 'Hello', y: 'bar'})
+```
+
+A `StampedTemplate` instance has the `fragment: DocumentFragment` property - the cloned contents of the template - and an `update(params: Record<string, unknown>): void` method - which when called will run the given processor again, with the new `params`.
+
+This library also comes with two ready-to-use processors: `propertyIdentity` and `propertyIdentityOrBooleanAttribute`. These processors implement a basic functionality that will replace expressions with the corresponding property value in the params object. You can use this processors rather than writing a custom one:
+
+
+```js
+import {StampedTemplate, propertyIdentity, propertyIdentityOrBooleanAttribute} from '@github/template-parts'
+
+// This will simply replace `{{x}}` with `"Hello"` and `{{y}}` with `"bar"`
+const tpl = new StampedTemplate(document.getElementById('foo'), propertyIdentity, { x: 'Hello', y: 'bar'})
+
+// The `propertyIdentityOrBooleanAttribute` processor will check for `false`/`true` values which map to attribute values, and add/remove the attribute.
+const tpl = new StampedTemplate(document.getElementById('foo'), propertyIdentityOrBooleanAttribute, { x: 'Hello', y: false})
+```