I am new to javascript and reactJS and I'm stuck. I have a javascript file where I make a REST call. The file looks like this:

```
var data;
function getDataRequest() {
 const request = new XMLHttpRequest();
    request.open('GET', "localhost:8080/getData", true);
    request.onload = function () {
        var data = JSON.parse(this.response);
        if (request.status >= 200 && request.status < 400) {
            products = data;
        } else {
            console.log('error');
        }
    };
    request.send();
}
var getDataList = function() {
    getDataRequest();
    return data;
};
getDataList();

```

And the file which contains the React component looks like this:

```
var = data;
class Datas extends React.Component {

    render() {
        data = this.getDataList;
        return (
            <DataTable data={data} />
        );
    }
}
export default Products;

```

The problem is that data in the React component remains 'undefined'. I am making the rest call in a different file because I want to call the rest call from multiple react components.