js.js

$(document).ready(function () {

    var firstLine = '';
    var secondLine = '';
    var result = 0;
    var startWithZero = /^0+/;
    var ifDecimalIncluded = /\./;
    var numberSpaceOnlyReg = /^(\s*|\d+|(\d+\.\d*))$/;
    var shouldOperation = /\d+$/;
    var shouldDecimal = /\d+$/;
    var shouldNotDecimal = /\.\d+$/
    var ifResult = /\=\-*(\d+|\d+\.\d+)$/;
    var ifDecimal = /\d+\.\d+$/;
    var ceRegEx = /(\d+|[\+\-\*\/]|\d+\.\d+|\d+\.)$/;
    var endWithOperator = /[\+\-\*\/]$/;
    var equalable = /^\D*\d+((\D\d+)*\D)\d+$/;
    var getLastSubStr = /\d+$/;
    var endWithNum = /\D*\d+$/;
    var onlyNum = /[\+\-\*\/]/
    var displayFirst = $('#firstline');
    var displaySecond = $('#secondline');

    // .attr('name'));
    var checkSpace = function () {
        var firstWidth = displayFirst.width();
        var secondWidth = displaySecond.width();
        var widthMax = 236;

        //max is reached,set to zero
        if (firstWidth >= 236 || secondWidth >= 236) {
            update('0', 'max length met');
            firstLine = secondLine = '';
        }
    }

    var update = function (first, second) {
        displayFirst.text(first);
        displaySecond.text(second);
    }

    //when number pad is click
    $('.number').on('click', function () {
        //case when last symbol is '='
        if (ifResult.test(secondLine)) {
            firstLine = $(this).attr('name');
            secondLine = $(this).attr('name');
            update(firstLine, secondLine);
            return;
        }
        //case when user enter numbers repetitively
        if (numberSpaceOnlyReg.test(firstLine)) {
            //check the edge case if start with number '0'
            if (startWithZero.test(firstLine) && !ifDecimalIncluded.test(firstLine)) {
                if (secondLine == '0') {
                    firstLine = secondLine = '';
                    return;
                }
                firstLine = $(this).attr('name');
                secondLine = secondLine.replace(ceRegEx, firstLine) == '' ? '0' : secondLine.replace(ceRegEx, firstLine);
                update(firstLine, secondLine);
                checkSpace();
                return;
            }

            firstLine += $(this).attr('name');
            secondLine += $(this).attr('name');
            update(firstLine, secondLine);
            checkSpace();
            return;
        }
        //case when last input is operators
        if (endWithOperator.test(secondLine)) {
            firstLine = $(this).attr('name');
            secondLine += $(this).attr('name');
            update(firstLine, secondLine);
            checkSpace();
            return;
        }

    })

    //when AC(all clear ) is clicked

    $('#AC').on('click', function () {
        //clear everything
        update('0', '0');
        firstLine = secondLine = '';
    })

    //when operator is clicked

    $('.operator').on('click', function () {
        //new operation after getting results;

        if (ifResult.test(secondLine)) {
            firstLine = $(this).text();
            secondLine = result + $(this).attr('name');
            update(firstLine, secondLine);
            return;
        }

        //do something when the last digit of second line is an operator
        if (shouldOperation.test(secondLine)) {
            firstLine = $(this).text();
            secondLine += $(this).attr('name');
            update(firstLine, secondLine)
        }
    })

    //when the "=" operator is click;
    $('.equal').on('click', function () {

        if (equalable.test(secondLine)) {
            result = ifDecimal.test(eval(secondLine)) ? eval(secondLine).toFixed(2) : eval(secondLine);
            firstLine = result;
            secondLine += '=' + result;
            update(firstLine, secondLine);
            checkSpace();
        }
    })

    //when . is clicked
    $('#last').on('click', function () {
        //if result
        if (ifResult.test(secondLine)) {
            firstLine = secondLine = '0.';
            update(firstLine, secondLine);
            return;
        }

        if ((shouldDecimal.test(secondLine) && !shouldNotDecimal.test(secondLine)) || secondLine == '') {
            firstLine = firstLine == '' ? '0.' : firstLine += '.';
            secondLine = secondLine == '' ? '0.' : secondLine += '.';
            update(firstLine, secondLine);
        }
    })

    // When CE button is clicked, clear the last entry only

    $('#CE').on('click', function () {
        //if only num no operator clear all

        if (!onlyNum.test(secondLine)) {
            update('0', '0');
            firstLine = secondLine = '';
            return;
        }

        //check if result
        if (ifResult.test(secondLine)) {
            update('0', '0');
            firstLine = secondLine = '';
            return;
        }

        //clear last entry only
        secondLine = secondLine.replace(ceRegEx, '') == '' ? '0' : secondLine.replace(ceRegEx, '');

        firstLine = '';
        update('0', secondLine);
        if (secondLine == '0') {
            //clear all lines
            firstLine = secondLine = '';
            return;
        }

        //if end with num after replace
        if (endWithNum.test(secondLine)) {
            firstLine = getLastSubStr.exec(secondLine);
            update('0', secondLine);
            return;
        }
    })


})