javascript中async await的用法

async和await必须成对出现，示例：

function file2txtArr(file) {
    var fr = new FileReader;
    fr.readAsText(file);
    return new Promise((resolve) => {
        fr.onload = function() {
            resolve(this.result.split('\n'));
        }
    });
    
}

async function(){
      let file = this.$refs.upload.$refs['upload-inner'].$refs.input;
      let loginWxArr = await file2txtArr(file.files[0]);
}