How can I return JavaScript XMLHttpRequest response?

Question

I have this code in my JavaScript HTTP client class:

export class HttpClient {
    constructor(url) {
        this.url = url;
        this.xhr = new XMLHttpRequest();
        this.xhr.onloadend = (event) => {
            console.log('ONLOADEND', this.xhr.response);
            return this.xhr.response;
        }
    }

    get(async, header) {
        return new Promise((resolve, reject) => {
            this.xhr.open('GET', this.url, async);
            this.xhr.send();
            console.log('RESPONSE', this.xhr.response);
            resolve(this.xhr.response);
        });
    }
}

In this code the get() method finished before the this.xhr.onloadend finished in the constructor.

In my class where I use this HttpClient class I use like this:

this.httpClient.get(true, this.header).then((result) => {
  // result is never get the xhr.response here
});

How can I return / resolve with the response after datas loaded?