load/inject scripts

load.js

const injectScript = (id,url,callback) => {
  const existingScript = document.getElementById(id)
  if (!existingScript) {
    const script = document.createElement('script')
    script.src = url
    script.id = id
    document.body.appendChild(script)
    script.onload = () => { 
      if (callback) callback()
    }
  }
  if (existingScript && callback) callback()
}

injectScript('react','https://unpkg.com/[email protected]/umd/react.production.min.js')
injectScript('react-dom','https://unpkg.com/[email protected]/umd/react-dom.production.min.js')
injectScript('emotion-core','https://unpkg.com/@emotion/[email protected]/dist/core.umd.min.js')
injectScript('emotion-styled','https://www.unpkg.com/@emotion/[email protected]/dist/styled-base.umd.min.js')
injectScript('main-script','app.js')