Property 'on' does not exist on type 'HTMLElement'.
To prevent this error you can write: var plotDiv: any = document.getElementById('myDiv'); plotDiv.on('plotly_relayout', ... document.getElementById('myDiv') return HTMLElement. This type doesn't contain method on because this method is added within plotly-latest.min.js. So in order to silence the typescript warning you can explicity say compile not to check types for plotDiv Another way is create type definition like: interface PlotHTMLElement extends HTMLElement { on(eventName: string, handler: Function): void; } var plotDiv = <PlotHTMLElement>document.getElementById('myDiv') plotDiv.on('plotly_relayout', function() { });