如何基于从本地存储

Question

//function to download pps_compress.txt from cloud server for global parameter set PPs 
function get_pps_params() 
{ 

    chrome.storage.local.get(['ppsParams'], function(result) { 
     if (typeof(result) !== "undefined" && result != null){ 
      ppsParams = _base64ToArrayBuffer(result.ppsParams); 
      console.log(ppsParams); 
      dfd_pps.resolve(); 
      return; 
     } 
    }); 

    if(ppsParams == null) 
    { 
     var oReq = new XMLHttpRequest(); 
     oReq.open("GET", CLOUD_SERVER + 'get_pps_params', true); 
     oReq.responseType = "arraybuffer"; 

     oReq.onload = function (oEvent) { 
      console.log("Got pps params compressed!"); 
      ppsParams = oReq.response; // Note: not oReq.responseText 
      chrome.storage.local.set({ppsParams: _arrayBufferToBase64(ppsParams)}); 
      dfd_pps.resolve(); 
     }; 

     oReq.send(); 
    } 
} 

另一个数据反应在上面的代码，我试图让一些参数为从本地存储varaible ppsParams推迟一个XMLHttpRequest，但我想发送请求到CLOUD_SERVER只如果本地存储请求失败，现在两者都正在执行，那么如何推迟XMLHttpRequest。

Answer 1

貌似chrome.storage.local.get是异步的，所以如下图所示

function get_pps_params() 
{ 

    chrome.storage.local.get(['ppsParams'], function(result) { 
     if (typeof(result) !== "undefined" && result != null){ 
      ppsParams = _base64ToArrayBuffer(result.ppsParams); 
      console.log(ppsParams); 
      dfd_pps.resolve(); 
     } 
     if(ppsParams == null) 
     { 
      var oReq = new XMLHttpRequest(); 
      oReq.open("GET", CLOUD_SERVER + 'get_pps_params', true); 
      oReq.responseType = "arraybuffer"; 

      oReq.onload = function (oEvent) { 
       console.log("Got pps params compressed!"); 
       ppsParams = oReq.response; // Note: not oReq.responseText 
       chrome.storage.local.set({ppsParams: _arrayBufferToBase64(ppsParams)}); 
       dfd_pps.resolve(); 
      }; 

      oReq.send(); 
     } 
     return; 
    }); 
}