I create a function for this. Maybe exists a better solutions for this?
function writeLog(operationIdentifier, prevResult, operationNumber, newResult) {
const logEntry = {
    operation: operationIdentifier,
    prevResult: prevResult,
    number: operationNumber,
    result: newResult,
};
logEntries.push(logEntry);
console.log(logEntries);
From this:
function add() {
    const enteredNumber = getUserNumberInput();
    const initialResult = currentResult;
    currentResult += enteredNumber;
    createAndWriteOutput('+', initialResult, enteredNumber);
    writeLog('ADD', initialResult, enteredNumber, currentResult);
}