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(JS) JavaScript
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(JS) JavaScript is the programming language that runs in the browser, which is used to build advanced interactive Web sites and applications for secure browser execution.

JS Quiz Exercise Lab

What is Javascript?

JavaScript is the scripting language of the Web.JavaScript is used in millions of Web pages to add functionality, validate forms, detect browsers, and much more.

What Javascript can do?

What Javascript can do? As: JavaScript gives HTML designers a programming tool JavaScript can put dynamic text into an HTML page JavaScript can react to events JavaScript can read and write HTML elements.
- JavaScript can be used to validate data
- JavaScript can be used to detect the visitor's browser
- JavaScript can be used to create cookies

What is a Javascript statement?

A JavaScript statement is a command to a browser. The purpose of the command is to tell the browser what to do.

What is the difference between XML and HTML?

XML is not a replacement for HTML. XML and HTML were designed with different goals:
1- XML was designed to transport and store data, with focus on what data is.
2- HTML was designed to display data, with focus on how data looks.
The difference is
HTML is about displaying information, while XML is about carrying information.

What is a javascript object?

A collection of data containing both properties and methods. Each element in a document is an object. Using the DOM you can get at each of these elements/objects and do some cool sh*t.

Describe what event bubbling is?

Event bubbling causes all events in the child nodes to be automatically passed to its parent nodes. The benefit of this method is speed because the code only needs to traverse the DOM tree once.

Describe what "this" is in JavaScript?

In JavaScript, 'this' normally refers to the object which 'owns' the method, but it depends on how a function is called.

What is the difference between == and === ?

The 3 equal signs mean "equality without type coercion". Using the triple equals, the values must be equal in type as well.

== is equal to
=== is exactly equal to (value and type)
0==false // true
0===false // false, because they are of a different type
1=="1" // true, auto type coercion
1==="1" // false, because they are of a different type
Resources for this answer:

http://longgoldenears.blogspot.com/2007/09/triple-equals-in-javascript.html

Where do you place your JavaScript on the page?

It may depend on what you are using it for. There is some debate on this but generally a good question to ask to get an understanding of the JS knowledge. Answers:

What is a closure?

Closures are expressions, usually functions, which can work with variables set within a certain context. Or, to try and make it easier, inner functions referring to local variables of its outer function create closures. Resources for this answer:

What is Global Namespacing?

Resources for this answer:

http://elegantcode.com/2011/01/26/basic-javascript-part-8-namespaces/

           

"1" + 2 + "3" + 4;

What does the above statement evaluate to?

10
1234
37

1234

4 + 3 + 2 + "1"

What does the above statement evaluate to?

10
4321
91

var foo = 1;
function bar() {
	foo = 10;
	return;
	function foo() {}
}
bar();
alert(foo);

What is alerted?

1
10
Function
undefined
Error

function bar() {
    return foo;
    foo = 10;
    function foo() {}
    var foo = 11;
}
alert(typeof bar());

What is alerted?

number
function
undefined
Error

Function

var x = 3;

var foo = {
    x: 2,
    baz: {
        x: 1,
        bar: function() {
            return this.x;
        }
    }
}

var go = foo.baz.bar;

alert(go());
alert(foo.baz.bar());

What is the order of values alerted?

1, 2
1, 3
2, 1
2, 3
3, 1
3, 2

3, 1

var x   = 4,
    obj = {
        x: 3,
        bar: function() {
            var x = 2;
            setTimeout(function() {
                var x = 1;
                alert(this.x);
            }, 1000);
        }
    };
obj.bar();

What value is alerted?

1
2
3
4
undefined

x = 1;
function bar() {
    this.x = 2;
    return x;
}
var foo = new bar();
alert(foo.x);

What value is alerted?

1
2
undefined

function foo(a) {
    alert(arguments.length);
}
foo(1, 2, 3);

What value is alerted?

1
2
3
undefined

var foo = function bar() {}; 
alert(typeof bar);

What value is alerted?

function
object
undefined

undefined

var arr = [];
arr[0]  = 'a';
arr[1]  = 'b';
arr.foo = 'c';
alert(arr.length);

What value is alerted?

1
2
3
undefined

function foo(a) {
    arguments[0] = 2;
    alert(a);
}
foo(1);

What value is alerted?

1
2
undefined

function foo(){}
delete foo.length;
alert(typeof foo.length);

What value is alerted?

number
undefined
object
Error

Number

var foo = function foo() {
    console.log(foo === foo);  
};
foo();

What is printed in the console?

true
false
ReferenceError

true

function aaa() {
    return
    {
        test: 1
    };
}
alert(typeof aaa());

What does the above alert?

function
number
object
undefined

undefined

Number("1") - 1 == 0;

What is the result?

true
false
TypeError

true

(true + false) > 2 + true;

What is the result?

true
false
TypeError
NaN

false

function bar() {
    return foo;
    foo = 10;
    function foo() {}
    var foo = '11';
}
alert(typeof bar());

What is alerted?

number
function
undefined
string
Error

function

"1" - - "1";

What is the result?

0
2
11
"11"

var x = 3;

var foo = {
    x: 2,
    baz: {
        x: 1,
        bar: function() {
            return this.x;
        }
    }
}

var go = foo.baz.bar;

alert(go());
alert(foo.baz.bar());

What is the order of values alerted?

1, 2
1, 3
2, 1
2, 3
3, 1
3, 2

3, 1

new String("This is a string") instanceof String;

What is the result?

true
false
TypeError

true

[] + [] + 'foo'.split('');

What is the result?

"f, o, o"
TypeError
["f", "o", "o"]
[][]["f", "o", "o"]

"f, o, o"

new Array(5).toString();

What is the result?

",,,,"
[]
"[]"

",,,,"

var myArr = ['foo', 'bar', 'baz'];
myArr.length = 0;
myArr.push('bin');
console.log(myArr);

What is printed in the console?

['foo', 'bar', 'baz']
['foo', 'bar', 'baz', 'bin']
['bin', 'foo', 'bar', 'baz']
['bin']

['bin']

String('Hello') === 'Hello';

What is the result?

true
false
TypeError

true

var x = 0;
function foo() {
    x++;
    this.x = x;
    return foo;
}
var bar = new new foo;
console.log(bar.x);

What is printed on the console?

ReferrenceError
TypeError
undefined
0
1

undefined

"This is a string" instanceof String;

What is the result?

true
false
TypeError

false

var bar = 1,
    foo = {};

foo: {
    bar: 2;
    baz: ++bar;
};
foo.baz + foo.bar + bar;

What is the result?

ReferenceError
TypeError
undefined
NaN
4
5

NaN

var myArr = ['foo', 'bar', 'baz'];
myArr[2];
console.log('2' in myArr);

What is the result of console.log?

true
false
ReferenceError

true

var arr = [];
arr[0]  = 'a';
arr[1]  = 'b';
arr.foo = 'c';
alert(arr.length);

What value is alerted?

1
2
3
undefined

10 > 9 > 8 === true;

What is the result?

true
false

false

function foo(a, b) {
    arguments[1] = 2;
    alert(b);
}
foo(1);

What value is alerted?

2
undefined
ReferenceError

undefined

NaN === NaN;

What is the result?

true
false
TypeError

false

What type of object system does JavaScript support?

Resources for this answer:

http://www.parrot.org/content/javascript-object-system

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JS Quiz Exercise Lab

(JS) JavaScript
Interview Questions and Anwsers

JS Quiz Exercise Lab

Are you sure you're ready for this Quiz ?

JavaScript Web Quiz By David Shariff

The Benefits of Front-End

JS Quiz Exercise Lab

(JS) JavaScript Interview Questions and Anwsers

JS Quiz Exercise Lab

Are you sure you're ready for this Quiz ?

JavaScript Web Quiz By David Shariff

The Benefits of Front-End

(JS) JavaScript
Interview Questions and Anwsers