TypeError: invalid ‘in’ operand obj

A weird JavaScript error that you may face when using Dojo Ajax for retrieving some JSON data from the server to render on the browser. This error happens because Dojo is unable to process the resulted JSON data which is the case when handleAs attribute is set to “text”.

In order to fix this error, set handleAs attribute to “json” instead of “text” as shown below in the example:

xhr.get({
	url: '/SomeServlet',
	handleAs: "json",
	timeout: 3000,
	load: function(data) { /* Success Handling */ },
	error: function(err) { /* Failure Handling */ }
});

This is my today’s two cent advice.

Back from JavaOne China 2013

JavaOne China

JavaOne China

I just get back from JavaOne China that was held in Shanghai 22-25 July 2013. JavaOne China is one of the biggest Java Conferences in Asia. The conference organization was good and there were a lot of attendees in the conference sessions.

JavaOne China

JavaOne China

I had the chance to present “Efficient JavaScript Unit Testing” in 23 July, the room of the session was full of attendees and I was really amazed by the energy, enthusiasm, and responsiveness of the attendees during the session.

Photo with Chinese Developers

Photo with Chinese Developers

The session went great and I was glad to give a free copy of my JavaScript Unit Testing book to one of the attendees who answered a JavaScript quiz at the end of the session.

I uploaded my session below:

Aside from the conference, Shanghai is a modern city that has many good places to visit, I had the chance to visit three places there:
1. Yuyuan Garden and Old Town Area:
Yuyuan Garden Photos

2. Jing Temple:
Jingle Temple Photos

3. Oriental Pearl TV Tower:
Oriental Pearl TV Tower Photos

JavaScript Quiz #7

Assume that we have the following short JavaScript code:

<script>
    var result = typeof("Hello" instanceof String);
    alert(result); //What is the output of the alert? 
	
    result = typeof typeof("Hello" instanceof String);
    alert(result); //What is the output of the alert? 
	
    result = typeof typeof typeof("Hello" instanceof String);
    alert(result); //What is the output of the alert? 	
</script>

What is the output of each alert?

Know the complete answer

JavaScript Quiz #5

This quiz covers some of the JavaScript operators in order to explain they can work together inside expressions. Assume that we have the following JavaScript code:

var object1 = {
    valueOf: function () {
	return 10;
    },
    toString: function () {
	return "object1";
    }
};

var object2 = {
    valueOf: function () {
	return 20;
    },
    toString: function () {
	return "object2";
    }
};

var object3 = {
    valueOf: function () {
	return 30;
    },
    toString: function () {
	return "object3";
    }
};

var result = (object2, object1, object3) + object1 +-- object1; 
alert(result);

What is the output of the alert?

Read the complete answer

JavaScript Quiz #4

Understanding JavaScript by example is useful for absorbing the different concepts of the language quickly. In this post, I will illustrate a JavaScript quiz in order to understand how JavaScript operators work together. Assume that we have the following JavaScript code:

var object1 = {
    valueOf: function () {
        return 1;
    },
    toString: function () {
        return "object1";
    }
};

var object2 = {
    valueOf: function () {
        return 2;
    },
    toString: function () {
        return "object2";
    }
};

alert((object2 > object1 +-- object1) + true); //What is the output of the alert?

What is the output of the alert?

Read the complete answer