camelCase01.js

const fs = require('fs');

const line = `OID
BATCH_NO
VENDOR_ID
CHANNEL_ID
STORE_ID
SITE_ID
TRANS_DATE
POS_NOS
SER_NOS
TRANS_TIME
GUI_NOS
ITEM_SER
SKU_NOS
TRANS_QTY
TAX_TYPE
TAX_TYPE_SKU
SALES_AMT
TAX_AMT
TAX_SALES_AMT
SALES_AMT_TOTAL
TAX_SALES_AMT_TOTAL
CONT_NO
COMM_RATE
COMM_AMT
PAY_AMT
PROC_STATUS
INSTALLMENT_CODE
SUB_DEPT
CLASS
SUB_CLASS
BANK_FEES_TYPE
BANK_FEES_AMT`;

const data = line.split('\n');
const snakeToCamel = (string) => {
    string = string.toLowerCase();
    return string.replace(/(_\w)/g, (m) => {
        return m[1].toUpperCase();
    });
}

const camelCase = data.map(e => snakeToCamel(e));
console.log(camelCase);

fs.writeFileSync('output.txt', camelCase.join('\n'));