[4.0] Remove dependency on Polymer library

[t2ym]

[4.0] Remove dependency on Polymer library

Status

• Part of t2ym/i18n-element#63
• WIP in 4.0-develop branch
• NPM package
  • npm install i18n-format@next or npm install i18n-format@4.0.0-pre.13
    • Depends on i18n-number@4.0.0-pre, wc-putty@0.1.0, lit-html@^1.0.0, make-plural@^4.3.0

Tasks

• Move @polymer/polymer from dependencies to devDependencies
• Drop Safari 9 support
• bower.json with BSD-2-Clause as license
• Add lit-html dependency
• Convert to lit-html rendering
  • Remove @polymer/polymer imports
  • Convert properties and observers
• Make these properties read-only
  • paramAttribute is slot
  • paramFormat is {n}
  • observeParams is true
    • Dummy setter for observeParams
• Support IE11 and Edge with custom elements v1 polyfill
  • Import a separate polyfill.js from an independent npm module for polyfill.js
    • Import npm package wc-putty
• Convert tests
  • No Polymer methods
  • Adjust some waits
• Convert demo
  • Remove intl from extraDependencies in polymer.json
• Documentation
  • Decent comments
  • API Docs page

Design Issues

• root property for shadowRoot to imitate a Polymer element
• Is importMeta property necessary? No

Issues

• document.createElement('i18n-format') fails with "The result must not have attributes"
  • Fix: Put off setting this.lang in the constructor to connectedCallback()
• Calling of _setupParams() is too early to collect the expected parameters in the local DOM
  • Fix: Put off this._setupParams() to connectedCallback()
• ShadyDOM misinterprets target of direct node.appendChild() as shadowRoot
  • Root Cause: If shadowRoot is attached, ShadyDOM unexpectedly performs appendChild() to shadowRoot instead of the node's local DOM
  • Fix: Put off attachShadow() to the first rendering