javascriptTutorials

Monday, January 9, 2017

20-More.. javascript concepts-Worker

https://www.html5rocks.com/en/tutorials/workers/basics/

http://www.thatjsdude.com/interview/js2.html

https://www.tutorialspoint.com/javascript/javascript_animation.htm

Sunday, December 25, 2016

19-Qs and As links

Javascript Questions links

http://upworktest.in/top-10-popular-test-answers/javascript-test-2016/( (167 questions))
http://www.freelancehelps.com/2015/09/javascript-test-answer-2015.html( has 88 question , same as in link 1.)
http://upworktestanswer2015.blogspot.com/2015/12/javascript-upwork-test-answers-of-2016.html (http://upworktestanswer2015.blogspot.com )
http://upworktestru.com/javascript_test_2016_upwork_answers_questions/
http://entireupworktestanswers.blogspot.com/2016/07/javascript-upwork-odesk-elance-test.html
http://kourge.net/node/130 (all "typeof" and "undefined" related QnAs)
http://answers-odesk.blogspot.com/2014/05/javascript-13-test-answer-for-odesk.html
http://upwork-odesk-answers.blogspot.com/2016/11/javascript-test-2016.html(167 exact same as 1. )

http://www.odeskupwork.tk/2016/08/javascript-questions-and-answers-2016.html

Application on Amazon RDS

http://www.w3schools.com/js/

Thursday, December 22, 2016

Javascript-18-JSON to JS Objects

Converting a JSON Text to a JavaScript Object

<html>

<body>

<h2>Create Object from JSON String</h2>

var text = '{"employees":[' +

'{"firstName":"John","lastName":"Doe" },' +

'{"firstName":"Anna","lastName":"Smith" },' +

'{"firstName":"Peter","lastName":"Jones" }]}';

obj = JSON.parse(text);

document.getElementById("demo").innerHTML =

obj .employees[1].firstName + " " + obj.employees[1].lastName;

</script>

</body>

</html>

Output : Anna Smith

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Note:

comments of the form //… or /*…*/ are not allowed in JSON. This answer is based on:

http://www.json.org

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Javascript-17-Hoisting Declaration, use strict keyword

Hoisting
(meaning, recognizing a variable prior to its declaration):

Javascript Hoists only declaration(var x;).
But , not initiations(var x=9; (or) x=9);

Example:

(a)
<body>
<p id="demo"></p>
<script>
x = 5; // Assign/initialize 5 to x
elem = document.getElementById("demo"); // Find an element
elem.innerHTML = x; // Display x in the element
var x; // Declare x
</script>
</body>

(b)
<body>
<p id="demo"></p>
<script>
var x; // Declare x
elem = document.getElementById("demo"); // Find an element
elem.innerHTML = x; // Display x in the element
x = 5; // Assign/initialize 5 to x
</script>
</body>

(a) results in "5", which is the value assigned for "x", though x has been defined after it is used. However, x has been initialized much before its usage.

(b) results in "undefined", though "x" has been defined before its usage. However, x has been initialized after its usage.

Hence, javascript hoists only for initializations and not declarations.

___________________________________

use strict;

This statement is used in order to ensure that the developer initializes and declares all his variables before its usage.

The "use strict" directive is only recognized at the beginning of a script or a function.

refer: http://www.w3schools.com/js/js_strict.asp to check onmore of the keyword notes

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Javascript-16-Regex

Regular Expression

Syntax: /pattern/modifiers;

pattern - the string pattern that needs to be searched

modifiers - the condition if any during the search for the pattern.

Regular Expression Modifiers:

i - Perform case-insensitive matching

g - Perform a global match (find all matches rather than stopping after the first match)

m - Perform multiline matching

Regular Expression Patterns:

[abc] - Find any of the characters between the brackets

[0-9] - Find digits in the range in the brackets

[x|y] - Find x or y giving in the bracket

Metacharacters:

Quantifiers:

______________________________________

Regular expressions can be used with 2 of String methods:

1)str.search(""); //returns index of first occurence

Example:

var str = "Visit W3Schools";
var n = str.search(/w3schools/i); // returns 6

2)str.replace(""); //returns string by replacing string occurence

Example:

var str = "Visit Microsoft!";
var res = str.replace(/microsoft/i, "W3Schools"); //returns Visit W3Schools! for "res" value

______________________________________

Regex Object and its methods:

test(): It searches a string for a pattern, and returns true or false, depending on the result.

var patt = /e/;
patt.test("The best things in life are free!");
(or)
/e/.test("The best things in life are free!");
Results in "true"

exec(): It searches a string for a specified pattern, and returns the found text. If text not found, returns null;

/e/.exec("The best things in life are free!");
Results in "e"

______________________________________

Javascript-15-Bitwise operations

Bitwise Operations

Notes:

JavaScript uses 32-bit signed numbers.

Bitwise AND : 1&1 = 1, else 0

Bitwise OR: 0|0 = 0, else 1

Bitwise XOR: 1^1 = 1, 0^0 = 1, else 0

Bitwise ~ :

~5 => (bitform of the number+ 1).

Another trick is, ~(number) = -(number+1). ie, ~5 = -(6)

Bitwise -(negation)

However, -(5) = retain last digit and swap the rest.

ie, -5

5 = 00000000000000000000000000000101

-5 = 11111111111111111111111111111011

(Zero Fill) Bitwise Left Shift (<<):

5 << 1 = 10; ie,

00000000000000000000000000000101

<<

1

=

00000000000000000000000000001010 (ie, 000..0(2power3)0(2power1)0

(Zero Fill) Right Shift (>>>):

5 >>> 1 = 2; ie,

00000000000000000000000000000101

>>>

1

=

00000000000000000000000000000010 (ie, 000..0(2power1)0 == 2)

(Sign Preserving) Bitwise Right Shift (>>):

-5 >> 1 = -3; ie,

11111111111111111111111111111011

>>

1

=

11111111111111111111111111111101 ---(a)

here's the trick,

shift 1 place in bit format to get (a) and

retain last digit after and

swap the rest. Now u get a decimal.

add -ve to the obtained decimal.. hence in the above case..

00000000000000000000000000000011 .. which is 3.

Now add -ve to 3.. hence -3

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Decimal to Binary function:

function dec2bin(dec){
return (dec >>> 0).toString(2);
}

Binary to Decimal function:

function bin2dec(bin){
return parseInt(bin, 2).toString(10);
}

______________________________________________

Javascript-14-For Loops

For Loops

For loop: for(initiation(optional),condition,increment(optional))

var i = 2;
len = cars.length;
var text = "";
for (; i < len; i++) {
text += cars[i] + "<br>";
}
If you omit statement 2, you must provide a break inside the loop. Otherwise the loop will never end. This will crash your browser.

For in: for(variableName in objectname)

var person = {fname:"John", lname:"Doe", age:25};
var text = "";
var x;
for (x in person) {
text += person[x];
}

It is a common mistake, among new JavaScript developers, to believe that this code returns undefined:

It is true in many programming languages, but not true in JavaScript.

Example:

for (var i = 0; i < 10; i++) {// some code}
return i;

The code returns value of i as "10", though ideally it is out of the for loop. Thats how it is in javascript

_____________________________________________________________

Monday, January 9, 2017

20-More.. javascript concepts-Worker

Sunday, December 25, 2016

19-Qs and As links

Thursday, December 22, 2016

Javascript-18-JSON to JS Objects

Converting a JSON Text to a JavaScript Object

Javascript-17-Hoisting Declaration, use strict keyword

Javascript-16-Regex

Regular Expression Modifiers:

Regular Expression Patterns:

Metacharacters:

Quantifiers:

Regex Object and its methods:

test(): It searches a string for a pattern, and returns true or false, depending on the result.

exec(): It searches a string for a specified pattern, and returns the found text. If text not found, returns null;

Javascript-15-Bitwise operations

Bitwise AND : 1&1 = 1, else 0

Bitwise OR: 0|0 = 0, else 1

Bitwise XOR: 1^1 = 1, 0^0 = 1, else 0

Bitwise ~ :

~5 => (bitform of the number+ 1).

Bitwise -(negation)

(Zero Fill) Bitwise Left Shift (<<):

5 << 1 = 10; ie, 00000000000000000000000000000101 << 1 = 00000000000000000000000000001010 (ie, 000..0(2power3)0(2power1)0

(Zero Fill) Right Shift (>>>):

5 >>> 1 = 2; ie, 00000000000000000000000000000101 >>> 1 = 00000000000000000000000000000010 (ie, 000..0(2power1)0 == 2)

(Sign Preserving) Bitwise Right Shift (>>):

Decimal to Binary function:

Binary to Decimal function:

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Javascript-14-For Loops

5 << 1 = 10; ie,

00000000000000000000000000000101

<<

1

=

00000000000000000000000000001010 (ie, 000..0(2power3)0(2power1)0

5 >>> 1 = 2; ie,

00000000000000000000000000000101

>>>

1

=

00000000000000000000000000000010 (ie, 000..0(2power1)0 == 2)