数组里有数据，但是打印出来的长度却是0

let data=[]
            for (let i = 0; i < this.fileList.length; i++){
              let reader = new FileReader();
              let fileResult = "";
              let name = this.fileList[i].name
              reader.readAsDataURL(this.fileList[i].raw);
              //开始转
              reader.onload = function() {
                fileResult = reader.result;
                let item = {
                  NAME : name,
                  IMAGE : fileResult,
                }
                data.push(item);
                // console.log(data.length)
              };
            }

 

setTimeout(() => {
  // console.log(data.length)
  this.$ept.Paperless.PostImage(data);
}, 1000);  //1秒后执行代码