JavaScript Advanced (2)

String objects

The Sting object is used to process the characters that are already in the block

JavaScript strings

anstring (computer science)It's used to store a series of characters like "John Doe".

A string can use either single or double quotes:

var carname="Volvo XC60";



var carname='Volvo XC60';

You use the position (index) to access any character in the string:

var character=carname[7];

Strings are indexed from zero, so the first character of the string is [0], the second character is [1], and so on.

You can use quotes in strings as in the following example:

var answer="It's alright";



var answer="He is called 'Johnny'";



var answer='He is called "Johnny"';

Or you can use the escape character (\) in a string using quotes:

var answer='It\s alright;'



var answer="He is called \"Johnny\"";

String (String)

String (String) uses the length attribute lenght to calculate the length of a string:

Example:

var txt="Hello World!"



();



var txt="ABCDEFGHIJKLMNOPQRSTUVWXYZ";



();

Conversion between String and Object:

an actual example

       



            



            var str3=new String("hello,world");



            //alert(typeof str3);// object type object



            //string--convert to -->object--use new String (string value)



            //object--convert to -->string--use toString() /valueoOf()--return the string of some string object



            var str4=();



            alert(typeof str4);

Finding a string within a string

Strings use indexOf() to locate the first occurrence of a specified character in a string:

Example.

var str="Hello world, welcome to the universe.";



var n=("welcome");

The function returns -1 if the corresponding character is not found.

The lastIndexOf() method starts at the end of the string to find the position where the string appears.

Content Matching

The match() function is used to find a specific character in a string and return that character if found.

Example.

var str="Hello world!";



(("world") + "<br>");



(("World") + "<br>");



(("world!"));

Replacement content

The replace() method replaces some characters with others in a string.

Example.

str="Please visit Microsoft!"



var n=("Microsoft","Runoob");

String Case Conversion

String case conversion using the toUpperCase() / toLowerCase() function.

Example.

var txt="Hello World!";       // String



var txt1=(); // txt1 text will be converted to upper case



var txt2=(); // txt2 text will be converted to lower case

String to Array

String usagesplit() function to an array.

Example.

txt="a,b,c,d,e"   // String



(","); // use comma separations



(" "); // use space separators



("|"); // use vertical lines to separate

special character

Javascript You can use backslashes (\) to insert special symbols, such as apostrophes, quotation marks, and other special symbols.

Check out the JavaScript code below.

var txt="We are the so-called "Vikings" from the north.";



(txt);

In JavaScript, strings start and stop with single or double quotes. This means that the above string will be cut into: We are the so-called

The solution to the above problem can be to use backslashes to escape quotes:

var txt="We are the so-called \"Vikings\" from the north.";



(txt);

JavaScript will output the correct text string: We are the so-called "Vikings" from the north.

The following table lists other special characters, and backslashes can be used to escape special characters:

String Object Properties 

String Object Methods 

String object methods

String HTML wrapper method

HTML returns the content contained in the corresponding HTML tag.

The following methods are not standard, so they may not be supported under some browsers.

  Date object

The date object is used to work with dates and times.

A Date object can be defined using the new keyword.

The following code defines a Date object named myDate

There are four ways to initialize the date

new Date();



new Date(value);



new Date(dateString);



new Date(year, monthIndex [, day [, hours [, minutes [, seconds [, milliseconds]]]]]);

Some examples of instantiating a date:

var today = new Date();



var d1 = new Date("October 13, 1975 11:13:00");



var d2 = new Date(79,5,24);



var d3 = new Date(79,5,24,11,33,0)

Setting the date

We can easily manipulate dates by using methods that target date objects.

In the following example, we set a specific date (January 14, 2010) for the Date object:

var myDate=new Date();



myDate.setFullYear(2010,0,14);

In the following example, we set the date object to a date 5 days from now:

var myDate=new Date();



myDate.setDate(myDate.getDate()+5);

Comparison of two dates

The date object can also be used to compare two dates.

The following code compares the current date to 1/14/2100:

var x=new Date();



x.setFullYear(2100,0,14);




var today = new Date();




if (x>today){




alert("Today is before January 14, 2100.");



}else{




alert("Today is after January 14, 2100.");



}

How do I format a date into a specified format?

Date.prototype.format = function (fmt) {



  var o = {



    "M+": () + 1,                   //months



    "d+": (),                        //date



    "h+": (),                       //hourly



    "m+": (),                     //ingredient



    "s+": (),                     //unit of angle or arc equivalent one sixtieth of a degree



    "q+": ((() + 3) / 3), 		//season (sports)



    "S": ()                  //millisecond



  };



  //  Get year



  // ①



  if (/(y+)/i.test(fmt)) {



    fmt = fmt.replace(RegExp.$1, (() + "").substr(4 - RegExp.$1.length));



  }



  for (var k in o) {



    // ②



    if (new RegExp("(" + k + ")", "i").test(fmt)) {



      fmt = fmt.replace(



        RegExp.$1, (RegExp.$1.length == 1) ? (o[k]) : (("00" + o[k]).substr(("" + o[k]).length)));



    }



  }



  return fmt;}



var now = new Date();



var nowStr = now.format("YYYY-MM-DD"); // 2021-01-11

Date object properties

 Date object methods

3. JavaScript Array (array) objects

Array objects are useful for storing a series of values using separate variable names.

What is an array?

An array object is a series of values stored using separate variable names.

If you have a set of data (e.g., car name), separate variables exist as shown below:

var car1="Saab";



var car2="Volvo";



var car3="BMW";

However, what if you wanted to identify a particular car from it? And not 3, but 300 cars? It would not be an easy task!

The best way to do this is with an array.

Arrays can store all values with a variable name and any value can be accessed with a variable name.

Each element in the array has its own ID so that it can be easily accessed.

Creating an Array

There are three ways to create an array.

The following code defines an array object named myCars:

1: General approach.

var myCars=new Array();



myCars[0]="Saab";      



myCars[1]="Volvo";



myCars[2]="BMW";

2: Simplicity.

var myCars=new Array("Saab","Volvo","BMW");

3: Literal.

var myCars=["Saab","Volvo","BMW"];

Access to arrays

You can access a particular element by specifying the array name as well as the index number.

The following example accesses the first value of the myCars array:

var name=myCars[0];

The following example modifies the first element of the array myCars.

myCars[0]="Opel";

[0] is the first element of the array. [1] is the second element of the array.

You can have different objects in an array

All JavaScript variables are objects. Array elements are objects. Functions are objects.

So you can have different variable types in the array.

You can include object elements, functions, and arrays in an array:

myArray[0]=Date.now;



myArray[1]=myFunction;



myArray[2]=myCars;

Creating a new method

A prototype is a JavaScript global constructor. It constructs the properties and methods of a new Javascript object.

Example: create a new method.

Array.prototype.myUcase=function(){



    for (i=0;i<this.length;i++){



        this[i]=this[i].toUpperCase();



    }



}

The above example creates a new array method for converting an array of lowercase characters to uppercase characters.

Array Properties

Array Object Methods

Boolean objects

The Boolean object is used to convert non-Boolean values to Boolean values (true or false).

Creating Boolean Objects

Boolean objects represent two values: "true" or "false".

The following code defines a Boolean object named myBoolean:

var myBoolean=new Boolean();

If the Boolean object has no initial value or its value is.

//var num1=10; // 0==false  in-0Numbers -true





//var str="hello"; // empty string==false  non-empty string==true 



var test1=null;  // null==false

Boolean Object Properties

Boolean object methods

Math objects

The Math (arithmetic) object does what it says: performs common arithmetic tasks.

The Math object provides a variety of arithmetic types and functions. There is no need to define the object before using it.

Syntax for using Math's properties/methods

var x=Math.PI;




var y=Math.sqrt(16);

Note: The Math object does not need to be defined before using this object.

Math Object Properties

Math Object Methods