This below code sample shows
how to load (SharePoint) JavaScript libraries
The SharePoint Framework (SPFx) is a page and web part model that
provides full support for client-side SharePoint development, easy integration
with SharePoint data and support for open source tooling. Import this below namespace in your solution.

Image Source:https://cdn-images-1.medium.com/max/1200/1*UOpi5-1883Iuu1Cx4PPBvg.png
import { SPComponentLoader } from '@microsoft/sp-loader';
Reference: https://github.com/SharePoint/sp-dev-fx-webparts/blob/4a4fccf69b075f4395230690d35bf45e0c4f5500/samples/react-taxonomypicker/src/controls/PropertyPaneTaxonomyPicker/components/TaxonomyPickerLoader.tsx
Private _loadSPJSOMScripts() { const siteColUrl = Utils.getSiteCollectionUrl(); try { SPComponentLoader.loadScript(siteColUrl + '/_layouts/15/init.js', { globalExportsName: '$_global_init' }) .then((): Promise<{}> => { return SPComponentLoader.loadScript(siteColUrl + '/_layouts/15/MicrosoftAjax.js', { globalExportsName: 'Sys' }); }) .then((): Promise<{}> => { return SPComponentLoader.loadScript(siteColUrl + '/_layouts/15/SP.Runtime.js', { globalExportsName: 'SP' }); }) .then((): Promise<{}> => { return SPComponentLoader.loadScript(siteColUrl + '/_layouts/15/SP.js', { globalExportsName: 'SP' }); }) .then((): Promise<{}> => { return SPComponentLoader.loadScript(siteColUrl + '/_layouts/15/SP.taxonomy.js', { globalExportsName: 'SP' }); }) .then((): void => { this.setState({ loadingScripts: false }); }) .catch((reason: any) => { this.setState({ loadingScripts: false, errors: [...this.state.errors, reason] }); }); } catch (error) { this.setState({ loadingScripts: false, errors: [...this.state.errors, error] }); } }