Now that we know how to find lists, we can change our code a bit. What we are doing next is checking if a list exists, and if it doesn't, we are going to create it.
Add the following function to your web part class.
private _createSharePointList(): void { const getListUrl: string = this.context.pageContext.web.absoluteUrl + "/_api/web/lists/GetByTitle('My List')"; this.context.spHttpClient.get(getListUrl, SPHttpClient.configurations.v1) .then((response: SPHttpClientResponse) => { if (response.status === 200) { alert("List already exists."); return; // list already exists } if (response.status === 404) { const url: string = this.context.pageContext.web.absoluteUrl + "/_api/web/lists"; const listDefinition : any = { "Title": "My List", "Description": "My description...