复制
1const getJSON = function(url) {
2  return new Promise((resolve, reject) => {
3    const xhr = XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject('Mscrosoft.XMLHttp');
4    xhr.open('GET', url, false);
5    xhr.setRequestHeader('Accept', 'application/json');
6    xhr.onreadystatechange = function() {
7      if (xhr.readyState !== 4) return;
8      if (xhr.status === 200 || xhr.status === 304) {
9        resolve(xhr.responseText);
10      } else {
11        reject(new Error(xhr.responseText));
12      }
13    }
14    xhr.send();
15  })
16}
17