Edit in JSFiddle

function createCookie(name,value,days) {
    if (days) {
        var date = new Date();
        date.setTime(date.getTime()+(days*24*60*60*1000));
        var expires = "; expires="+date.toGMTString();
    }
    else var expires = "";
    document.cookie = name+"="+value+expires+"; path=/";
    return true;
}

function readCookie(name) {
    var nameEQ = name + "=";
    var ca = document.cookie.split(';');
    for(var i=0;i < ca.length;i++) {
        var c = ca[i];
        while (c.charAt(0)==' ') c = c.substring(1,c.length);
        if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
    }
    return null;
}

function showCookie(name)
{
    if(!name) {
        alert('\nPlease enter the name of cookie in the  cookie name field.');
        return false;
    }
    var val = readCookie(name);
    if(val){
        alert(readCookie(name));
    }
    else alert('Cookie "' + name + '" doesn\'t exist!');
}

function eraseCookie(name) {
    if(!name) {
        alert('\nPlease enter the name of cookie in the  cookie name field.');
        return false;
    }
    if(readCookie(name)){
        if(createCookie(name,"",-1)) {
            alert('Cookie "' + name + '" has been deleted!');        
        }
    }
    else alert('Cookie "' + name + '" doesn\'t exist!');
}

function addCookie()
{
    cookie_name = document.getElementById("cName").value.replace(/^\s+|\s+$/g,'');
    cookie_value = document.getElementById("cValue").value.replace(/^\s+|\s+$/g,'');
    if(cookie_name.length && cookie_value.length){
        createCookie(cookie_name, cookie_value, 7);
        alert("New cookie has been added, \ncookie name : " + cookie_name + "\ncookie value : " + cookie_value);
    }
    else{
        alert("Please enter a name and value for the cookie.");
    }
}
if(name = readCookie('name')) alert('Welcome back, ' + name);

Cookie Name: <input type="text" id="cName" /> Cookie Value: <input type="text" id="cValue" />
<input type="button" value="Add" onClick="addCookie()" />
<input type="button" value="View" onClick="showCookie(document.getElementById('cName').value)" />
<input type="button" value="Delete" onClick="eraseCookie(document.getElementById('cName').value)" />