how to get the sum of numbers via map? : 
How to get the sum of elements (numbers) that I get from the database?

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

    	const onSum = () => {
      return invoiceList.map(i => {
        // i.number summ
      })
    };

<!-- language: lang-html -->

    <script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>


<!-- end snippet -->

