原生js 封装get ,post, delete 请求的实例

function api(url,opt,methods) {
      return new Promise(function(resove,reject){
        methods = methods || 'POST';
        var xmlHttp = null;
        if (XMLHttpRequest) {
          xmlHttp = new XMLHttpRequest();
        } else {
          xmlHttp = new ActiveXObject('Microsoft.XMLHTTP');
        };
        var params = [];
        for (var key in opt){
          if(!!opt[key] || opt[key] === 0){
            params.push(key + '=' + opt[key]);
          }
        };
        var postData = params.join('&');
        if (methods.toUpperCase() === 'POST') {
          xmlHttp.open('POST', url, true);
          xmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded;charset=utf-8');
          xmlHttp.send(postData);
        }else if (methods.toUpperCase() === 'GET') {
          xmlHttp.open('GET', url + '?' + postData, true);
          xmlHttp.send(null);
        }else if(methods.toUpperCase() === 'DELETE'){
          xmlHttp.open('DELETE', url + '?' + postData, true);
          xmlHttp.send(null);
        }
        xmlHttp.onreadystatechange = function () {
          if (xmlHttp.readyState == 4 && xmlHttp.status == 200) {
            resove(JSON.parse(xmlHttp.responseText));
          }
        };
      });
    }
    export default api;