for google inbox, select all and delete all buttons

gmailMarkAll.user.js

// ==UserScript==
// @name        gmail mark read
// @match       https://inbox.google.com/*
// @version     1.0.3
// @grant       none
// @namespace   https://gist.github.com/Mido22
// @downloadURL https://gist.github.com/Mido22/5b14c63636b3874902e47a8e1f6c4f74
// ==/UserScript==

(function(w, d){
  'use strict'

  let cget = 'getElementsByClassName'

  w.addEventListener('load', () => {
		addButton('select read', selectReadFn)
		addButton('select all', selectAll, {left:'18%'})
		addButton('delete all', delAll, {bottom: '10%', left:'18%'})
		addButton('delete read', delRead, {bottom: '10%'})
	})

	function delAll() {
		selectAll();
		deleteMails();
	}

	function delRead() {
		selectReadFn();
		deleteMails();
	}

	function addButton(text, onclick, cssObj) {
		cssObj = cssObj || {}
		let dflt = {position: 'fixed', bottom: '7%', left:'13%', 'z-index': 3}
		Object.keys(dflt).filter(k => !cssObj[k]).forEach(k => cssObj[k]=dflt[k])
		let button = d.createElement('button'), btnStyle = button.style
		d.body.appendChild(button)
		button.innerHTML = text
		button.onclick = onclick
		btnStyle.position = 'absolute'
		Object.keys(cssObj).forEach(key => btnStyle[key] = cssObj[key])
		return button
	}

	function selectReadFn() {
		[...d[cget]('MN')].filter(isRead).forEach(e => e.click())
	}

	function deleteMails() {
		d.querySelector('.itemIconTrash').click()
	}

	function selectAll() {
		[...d[cget]('MN')].forEach(e => e.click())
	}

	function isRead(e) {
		let p = 'parentElement'
		return ![...e[p][p][p][cget]('G3')].some(e => e.innerText.search(/unread/i)!==-1)
	}

}(window, document))