JS ScriptLoader using ES6 Promises

scriptloader.js

function ScriptLoader () {
  const loader = url => new Promise((resolve, reject) => {
    const script = document.createElement('script')
    script.src = url
    script.async = !0
    script.addEventListener('load', resolve(script), !1)
    script.addEventListener('error', reject(script), !1)
    body.appendChild(script)
  })
  this.load = url => loader(url)
}

const loginBtn = document.querySelector('h1')
loginBtn.addEventListener('click', () => {
  const loader = new ScriptLoader()
  loader.load([
    'slider.js'
  ]).then(() => console.log('loaded!'))
})

Load script only once:

let scriptsloaded = ''
function ScriptLoader () {
  if (criptsloaded.indexOf(`[${url}]`) === -1) {
    const loader = url => new Promise((resolve, reject) => {
      const script = document.createElement('script')
      script.src = url
      script.async = !0
      script.addEventListener('load', resolve(script), !1)
      script.addEventListener('error', reject(script), !1)
      body.appendChild(script)
    })
    this.load = url => loader(url)
    scriptsloaded += `[${url}]`
  }
}