FileReader

undefined check

if(typeof obj === undefined)

if(obj === 'undefined')

input type file

check file selected

if(document.getElementById('file').value === '') {

alert('please select file')

}

read text file

function readFile() {
    const fObj = document.getElementById("file");
    console.log(fObj.value);
    if(fObj.value === '') {
        alert('파일을 선택해주세요.');
    } else {
        const selectedFile = fObj.files[0];
        console.log(selectedFile);
        console.log('Name :' + selectedFile.name + '/ Size : ' + selectedFile.size);

        var reader = new FileReader();
        reader.onload = function(evt) {
            if(evt.target.readyState == FileReader.DONE) {
                console.log(evt);
                console.log(reader.result);
            }
        };
        reader.readAsText(selectedFile);
    }
}

read excel file - using sheetjs - need a check

function readExcelFile() {
    const fObj = document.getElementById("file");
    console.log(fObj.value);
    if(fObj.value === '') {
        alert('파일을 선택해주세요.');
    } else {
        const selectedFile = fObj.files[0];
        console.log(selectedFile.path);
        console.log('Name :' + selectedFile.name + '/ Size : ' + selectedFile.size);

        var reader = new FileReader();

        reader.onload = function(evt) {
            if(evt.target.readyState == FileReader.DONE) {
                console.log(reader.result);
                //var workbook = XLSX.read(reader.result, {type: 'binary'});

                var data = evt.target.result;
                //data = new Uint8Array(data);

                // call 'xlsx' to read the file
                var workbook = XLSX.read(data, {type: 'binary'});

                //var workbook = XLSX.readFile(selectedFile.path, {type: 'binary'});
                console.log(workbook);
                //var toHtml = XLSX.utils.sheet_to_html(workbook.Sheets['Sheet1'], {header:1});
                //document.getElementById('grid').innerHTML = toHtml;
            }
        };
        reader.readAsArrayBuffer(selectedFile);
        reader.readAsBinaryString(selectedFile);
    }
}