Edit in JSFiddle

var myArray = new Array();
myArray.push("Hello World");
var length = myArray.push("Cheers !!");
$("#arrayElements").text(myArray);
$("#arrayLength").text("Array Length : " + length);

$("#pushButton").click(function () {
    var textToAdd = $("#userInput").val();
    if (textToAdd != "") {
        $("#errorMessage").text("");
        var newLength = myArray.push(textToAdd);
        $("#arrayElements").text(myArray);
        $("#arrayLength").text("Array Length : " + newLength);
    } else {
        $("#errorMessage").text("Please enter valid input");
    }
});
<p id="errorMessage"></p>
<p id="arrayElements"></p>
<p id="arrayLength"></p>
<input type="text" id="userInput" />
<input type="button" id="pushButton" Value="Push" />
#errorMessage {
    color:Red;
}