code snippet about papago resutful api in javascript

papago.js

new Promise((resolve, reject) => {
        var xhr = new XMLHttpRequest();
        xhr.open("POST", 'https://openapi.naver.com/v1/papago/n2mt');
        var myHeader = Object.assign({ 'Content-Type': 'application/x-www-form-urlencoded' }, GetPapagoSecert());
        for (var key in myHeader) {
            xhr.setRequestHeader(key, myHeader[key]);
        }

        xhr.onreadystatechange = function() {
            if (xhr.readyState == 4) {
                if (xhr.status === 200) {
                    resolve(xhr.responseText);
                } else {
                    if (xhr.status === 500) {
                        console.error(xhr.responseText)
                    }
                    reject(xhr.status);
                }
            }
        }

        var myBody = Object.assign(GetRegion(text), { 'text': text });
        var data = [];
        for (var key in myBody) {
            data.push(`${key}=${myBody[key]}`);
        }
        data = data.join('&');

        log(`request => ${data}`);

        xhr.send(data);
    })