Wait for a Script to Load in Javascript

export default class ScriptLoader { constructor (options) { const { src, global, protocol = document.location.protocol } = options this.src = src this.global = global this.protocol = protocol this.isLoaded = false } loadScript () { return new Promise((resolve, reject) => { // Create script element and set attributes const script = document.createElement('script') script.type = 'text/javascript' script.async = true script.src = `${this.protocol}//${this.src}` // Append the script to the DOM const el = document.getElementsByTagName('script')[0] el.parentNode.insertBefore(script, el) // Resolve the promise once the script is loaded script.addEventListener('load', () => { this.isLoaded = true resolve(script) }) // Catch any errors while loading the script script.addEventListener('error', () => { reject(new Error(`${this.src} failed to load.`)) }) }) } load () { return new Promise(async (resolve, reject) => { if (!this.isLoaded) { try { await this.loadScript() resolve(window[this.global]) } catch (e) { reject(e) } } else { resolve(window[this.global]) } }) } } 

const loader = new Loader({ src: 'cdn.segment.com/analytics.js', global: 'Segment', }) // scriptToLoad will now be a reference to `window.Segment` const scriptToLoad = await loader.load()