JS string encoding convert, with iconv-lite and jschardet.

encoding_conv.js

const reader = new FileReader()
const file = this.uploadInput.files[0]
let self = this
reader.onload = function()
{
    let target_data = ''
    const data_info = jschardet.detect(reader.result)
    if('ascii'==data_info.encoding && data_info.confidence > 0)
        target_data = this.result
    else    
        target_data = iconv.decode(Buffer.from(this.result, 'binary'), 'GB18030')        
    })
}
reader.readAsText(file)