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Checking if a key exists in a JavaScript object?

How do I check if a particular key exists in a JavaScript object or array?

If a key doesn't exist, and I try to access it, will it return false? Or throw an error?

Most elegant way to clone a JavaScript object

I have an object x. I'd like to copy it as object y, such that changes to y do not modify x.

What's the most elegant way of doing this in JavaScript?

Edit:

I realized that copying objects derived from built-in JavaScript objects will result in extra, unwanted properties. This isn't a problem, since I'm copying one of my own, literal-constructed objects.

Interview: Can we instantiate abstract class?

The interviewer asked - Can we instantiate an abstract class? I said, No. He told me - Wrong, we can.

I argued a bit on this. Then he told me to try this yourself at your home.

abstract class my {
    public void mymethod() {
        System.out.print("Abstract");
    }
}

class poly {
    public static void main(String a[]) {
        my m = new my() {};
        m.mymethod();
    }
}

Here, I'm creating instance of my class and calling method of abstract class. Can anyone please explain this to me? Was I really wrong during my interview?

What is the most efficient way to clone an object?

What is the most efficient way to clone a JavaScript object? I've seen obj = eval(uneval(o)); being used, but that's currently Firefox-only. In Mootools 1.2, I've done things like obj = JSON.parse(JSON.stringify(o)); but question the efficiency.

I've also seen recursive copying functions with various flaws. I'm surprised no canonical solution exists.

Object comparison in JavaScript [duplicate]

Possible Duplicate:
How do you determine equality for two JavaScript objects?

What is the best way to compare objects in JavaScript?

Example:

var user1 = {name : "nerd", org: "dev"};
var user2 = {name : "nerd", org: "dev"};
var eq = user1 == user2;
alert(eq); // gives false

I know that two objects are equal if they refer to the exact same object, but is there a way to check if they have the same attributes' values?

The following way works for me, but is it the only possibility?

var eq = Object.toJSON(user1) == Object.toJSON(user2);
alert(eq); // gives true

Find object by id in an array of JavaScript objects

I've got an array:

myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}, etc.]

I'm unable to change the structure of the array. I'm being passed an id of 45, and I want to get 'bar' for that object in the array.

How do I do this in JavaScript or using jQuery?

Converting an object to a string

How can I convert a JavaScript object into a string?

Example:

var o = {a:1, b:2}
console.log(o)
console.log('Item: ' + o)

Output:

Object { a=1, b=2} // very nice readable output :)
Item: [object Object] // no idea what's inside :(

Python: How to print a class or objects of class using print()?

I am learning the ropes in Python. When I try to print an object of class Foobar using the print() function, I get an output like this:

<__main__.Foobar instance at 0x7ff2a18c>

Is there a way I can set the printing behaviour (or the string representation) of a class and its objects? For instance, when I call print() on a class object, I would like to print its data members in a certain format. How to achieve this in Python?

If you are familiar with C++ classes, the above can be achieved for the standard ostream by adding a friend ostream& operator << (ostream&, const Foobar&) method for the class.

Sort array of objects by object fields

How can I sort this array of objects by one of its fields, like name or count ?

  Array
(
    [0] => stdClass Object
        (
            [ID] => 1
            [name] => Mary Jane
            [count] => 420
        )

    [1] => stdClass Object
        (
            [ID] => 2
            [name] => Johnny
            [count] => 234
        )

    [2] => stdClass Object
        (
            [ID] => 3
            [name] => Kathy
            [count] => 4354
        )

   ....

check if object property exists - using a variable

checking for existence of javascript object property with a variable as part of the object name.

var myObj;
myObj.prop = "exists";
var myProp = "p"+"r"+"o"+"p";

if(myObj.myProp){
    alert("yes, i have that property");
};

This is undefined because it's looking for myObj.myProp when i want it to check for myObj.prop

Why is null an object and what's the difference between null and undefined?

Why is null considered an object in JavaScript?

Is checking

if ( object == null )
      Do something

the same as

if ( !object )
      Do something

?

And also:

What is the difference between null and undefined?

What is the JavaScript equivalent of var_dump or print_r in PHP?

I would like to see the structure of object in JavaScript (for debugging). Is there anything similar to var_dump in PHP?

Check if a variable is a string

I am currently using the isNaN function to check if my variable is a string or an object. I just wondered if this is the wrong way of doing it because it does not seem to be working.

if(isNaN(element))
    element = document.querySelector(element);

At the moment even if element is an object it is still causing isNaN to return true. Any ideas? I am sure I am missing something obvious. Is it that isNaN only works for a string/integer test?

Detecting an undefined object property

What's the best way of checking if an object property in JavaScript is undefined?

Convert Python dict to object?

I'm searching for an elegant way to convert a normal Python dict with some nested dicts to an object.

For example:

>>> d = {'a': 1, 'b': {'c': 2}, 'd': ["hi", {'foo': "bar"}]}

Should be accessible in this way:

>>> x = dict2obj(d)
>>> x.a
1
>>> x.b.c
2
>>> x.d[1].foo
bar

I think, this is not possible without recursion, but what would be a nice way to get an objectstyle for dicts?

Thank you in advance.