app.js

var operations = ['+','-','X','/'];

function calculate(){
    var previousText = $('#screen').text();
    var lastChar = previousText.slice(-1);
    if (_.contains(operations, lastChar)){
        previousText = previousText.substring(0,previousText.length - 1);
    }
    previousText = previousText.replace(/X/g,'*')/*.replace(...)saad edasi panna*/
    /*see, mida muuta tahad on / vahel ja g on nagu global ja ' vahel on see, mida muuta soovid*/
    return eval(previousText);
}
function showCurrentResult(){
    var result = calculate();
    $('#correct').text(result);
    if(result>=10 && result<=20){
        $('#correct').css('background','green');
    } else {
        $('#correct').css('background','red');
    }
}
$('#buttons span').click(function(){
    var inputText = $(this).text();
    var previousText = $('#screen').text();
    var lastChar = previousText.slice(-1);

    if(_.contains(operations,inputText)){
        //tegeleb tehetega
        if (_.contains(operations, lastChar)){
            previousText = previousText.substring(0,previousText.length - 1);
        }
        $('#screen').text(previousText + inputText);
    }
    else if (inputText == '='){
        //tegeleb kokkuarvutamisega
        $('#screen').text(calculate());
    }else{
        //lisab numbri
        $('#screen').text(previousText + inputText);
    }
    showCurrentResult();
});

$('#top span').click(function(){
    $('#screen').text('');
});