myApp.js

(function () {
    
    var ns = window.ns = {};
    
    var calcForm = document.calc;
    var expr = '';

    ns.NumPressed = function (symb) {

        if(calcForm.ReadOut.value === '0'){
            calcForm.ReadOut.value = '';
        }

        console.log(calcForm.ReadOut.value);
        calcForm.ReadOut.value += symb;
        expr = expr + symb;
        console.log(expr);    

    }


    ns.Neg = function() {



        var expArr = expr.split('');

        for (var i = expArr.length-1; i >= 0; i--){

            var buf = expArr[i];

            if(buf === '-'){

                expArr[i] = '+';
                expr = expArr.join('');
                console.log(expr);
                calcForm.ReadOut.value = expr;
                return;
            }

            if(buf === '+'){

                    expArr[i] = '-';
                    expr = expArr.join('');
                    console.log(expr);
                    calcForm.ReadOut.value = expr;
                    return;
                }

            if( buf === '*' ||
                buf === '/' ||
                buf === '%' ) {

                    shiftRight(i+1, '-');
                    console.log(expr);
                    calcForm.ReadOut.value = expr;
                    return;
                }

            if (i === 0){

                expArr.unshift('-');
                expr = expArr.join('');
                console.log(expr);
                calcForm.ReadOut.value = expr;
                return;
            }

        }

    }


    function shiftRight (pos , symb){

        var expArr = expr.split('');
        expArr.push(' ');

        for (var i = expArr.length-1; i > pos; i--){
            expArr[i] = expArr[i-1];
        }
        expArr[pos] = symb;
        expr = expArr.join('');
    }

    ns.Operation = function (operation){

            calcForm.ReadOut.value = '0';
        
        if (operation === '='){
            
            var buf = eval(expr);
            
            switch (buf) {
            
                case undefined:
                    calcForm.ReadOut.value = '0';
                    return;
                case Infinity:
                    calcForm.ReadOut.value = 'Zero devide!!!';
                    return;
            
            } 

            console.log(eval(expr));
            calcForm.ReadOut.value = eval(expr);
            expr = eval(expr).toString();
            return;

        }

        var expArr = expr.split('');
        var buf = expArr[expArr.length-1];

        if (buf === '*' ||
            buf === '/' ||
            buf === '%' || 
            buf === '+' ||
            buf === '-' ) {

            expArr[expArr.length-1] = operation;
            expr = expArr.join('');
            console.log(expr);
            return;
        }

        if (operation === 'sqrt'){(function () {

            var expArr = expr.split('');

            for (var i = expArr.length-1; i >=0; i--){
                var buf = expArr[i];
                var sqrtExpr = '';

                if (buf === '*' ||
                    buf === '/' ||
                    buf === '%' || 
                    buf === '+' ||
                    buf === '-' ||
                    i === 0) {

                    for (var j = i+1; j <= expArr.length-1; j++) sqrtExpr += expArr[j];
                    break;

                }


            }

            sqrtExpr = Math.sqrt(sqrtExpr);
                expArr.length = i+1;
                expr = expArr.join('');
                this.expr += sqrtExpr;
                console.log(expr);
                calcForm.ReadOut.value = sqrtExpr;

            }())

            return; 
        }


        expArr.push(operation);
        expr = expArr.join('');
        console.log(expr);

    }


    ns.ClearEntry = function () {

        expr = '';
        calcForm.ReadOut.value = '0';

    }


    ns.Clear = function () {

        var expArr = expr.split('');
        for (var i = expArr.length-1; i >= 0; i--){

            var buf = expArr[i];

            if (buf === '*' ||
                buf === '/' ||
                buf === '%' || 
                buf === '+' ||
                buf === '-' ||
                i === 0) {

                expArr.length = i;
                expr = expArr.join('');
                console.log(expr);
                calcForm.ReadOut.value = '0';
                return;

            }
        }


    }  
       
}())