How to dynamically load and use/call a JavaScript file?

Question

I need to dynamically load a JavaScript file and then access its content.

File test.js

test = function () {
    var pub = {}
    pub.def         


        

Answer 1

NOTE: there was one similar solution but it doesn't check if the script is already loaded and loads the script each time. This one checks src property and doesn't add script tag if already loaded. Loader function:

  const loadCDN = src =>
    new Promise((resolve, reject) => {
      if (document.querySelector(`head > script[src="${src}"]`) !== null) return resolve()
      const script = document.createElement("script")
      script.src = src
      script.async = true
      document.head.appendChild(script)
      script.onload = resolve
      script.onerror = reject
    })

Usage (async/await):

await loadCDN("https://.../script.js")

Usage (Promise):

loadCDN("https://.../script.js").then(res => {}).catch(err => {})