Convert excel to json in Vuejs

Question

I want to convert excel file to json but it shows error saying : Type Error ..cannot read the property 'target' of undefined

I tried all that I could but couldn't get rid of this error. There is no documentation for the same anywhere.

Below is my code

<template>
    <div>
    <div class="conatiner mt-5">
    <div class="row"> 
    <div class="col-md-3"></div> 
    <div class="col-md-3">
    <input class="form-control" type="file" id="input" accept=".xls, .xlsx" /> 
    </div> 
    <div class="col-md-2"> 
    <button class="btn btn-primary" id="button" v-on:click="previewFiles()">Convert</button> 
    </div> 
    <div class="col-md-12"> 
    <pre id="jsondata"></pre> 
    </div> 
    </div> 
    </div> 
    </div> 
    </template>

 <script> 
 export default {
 data() {
 return {}; 
}, 
function() { 
 oFileIn = document.getElementById('my_file_input');
if(oFileIn.addEventListener(){ oFileIn.addEventListener('change',   filePicked, false);

 } },
methods:{ 
previewFiles(e){
// Get The File From The Input var oFile = e.target.files[0];
var sFilename = oFile.name; 
// Create A File Reader HTML5 
var reader = new FileReader();
// Ready The Event For When A File Gets Selected 
reader.onload = function(e) { var data = e.target.result; 
var cfb = XLS.CFB.read(data, {type: 'binary'});
 var wb = XLS.parse_xlscfb(cfb);
 // Loop Over Each Sheet                 wb.SheetNames.forEach(
function(sheetName)
 { 
// Obtain The Current Row As CSV
 var sCSV =     XLS.utils.make_csv(wb.Sheets[sheetName]); 
var oJS = XLS.utils.sheet_to_row_object_array(wb.Sheets[sheetName]); 
$("#my_file_output").html(sCSV);    console.log(oJS) }); };     reader.readAsBinaryString(oFile) }, 
// Tell JS To Start Reading The File.. You could delay this if desired 
}, 
}; 
</script>

Please help me out with this.. Thanks in advance!!