javascript strings object

7/28/2019 JavaScript Strings Object

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Strings Object , Substring Method &

Regular Expression

Presented by - Amit KumarChandra Bhushan

JavaScript Presentation on


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JavaScript 2

Objectives

How to modify strings with common string method

Creating dynamic effect with Substring method

How to use the Regular expression with example


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JavaScript 3

JavaScript String Object

String Object

A string is any text inside a quote pair

A quote pair consists of either double or single quotes.

This allows one string to nest inside another, as often happens withevent handlers.

onclick = alert(Hello all)

JavaScript imposes no practical limit on the number of

characters that a string can hold.

Most olderbrowser have a limit of 255 characters in length

for a script statement.

You may need to divide these lines into smaller chunks


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JavaScript 4


You have two ways to assign a string value to a

variable:

var myString = Howdy;

var myString = new String(Howdy); As of Navigator 3 and IE 4

Joining Strings

Bringing two strings together as a single string is called

concatenation

The addition operator (+) links multiple strings together


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Concatenation Example:

var msg = AMIT;

msg = msg + KUMAR;msg = msg + SINGH;

The pieces can be combinations of string

literals (text inside quotes) or string variables.


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The add-by-value operator (+=) provides ashortcut.

var msg = AMIT;

msg += KUMAR;msg += SINGH;

You can also combine the operators if the need

arises:var msg = AMIT;

msg += KUMAR + SINGH;


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String Methods The String object has the most diverse collection of

methods associated with it (851-852).

To use a string method, the string being acted upon

becomes part of the reference followed by the methodname var result =string.methodName();

Changing String Case Methods To convert to Uppercase

var result =string.toUpperCase(); To convert to Lowercase

var result =string.toLowerCase();


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These methods come in handy when your

scripts need to compare strings that may not

have the same case.

A string in a lookup table verses a string entered

by a user

Because the methods dont change the original

strings attached to the expressions, you can simplycompare the evaluated results of the methods.


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var foundMatch = false;stringA = "test";

stringB = "TeST";

var stringC = ; //Null string

if (stringA.toUpperCase() = = stringB.toUpperCase())

foundMatch = true;

document.write(foundMatch);

stringC=stringA.toUpperCase();

document.write("
" + stringC)

Produces:

true

TEST


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String Searches

You can use the string.indexOf() method to see if

one string is contained by another

document.write(navigator.userAgent + "
");

document.write(navigator.userAgent.indexOf("Windows"));

Produces

Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; Q312461; SV1; .NET CLR 1.1.4322)

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If no match appears a value of -1 is returned.

You can use this fact to test if a string is nested in another string


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Extracting copies of character and substrings To extract or examine a single character at a know position within a string, use thecharAt() method

var stringA = Building C;

var bldgLetter = stringA.charAt(9);

//results would be the letter C

Another method, string.substring(), enables the extraction of a sequence of characters.

NOTE: The character at the ending position is not included in the extracted string.

var stringA = banana daiquiri;

var excerpt = stringA.substring(2, 6); //6-2 = 4 characters extracted

//result: excerpt = nana;

The number 2 desiganted the straring position of the extracted string (index begins atzero)

The number 6 designates the number of charters to extract


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Methods of the String Object

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ccMethod DescriptioncharAt( index ) Returns a string containing the character at the specified index. If there is no

character at the index, charAt returns an empty string. The first character islocated at index 0.

charCodeAt( index ) Returns the Unicode value of the character at the specified index. If there isno character at the index, charCodeAt returns NaN (Not a Number).

concat( string ) Concatenates its argument to the end of the string that invokes the method.

The string invoking this method is not modified; instead a new String isreturned. This method is the same as adding two strings with the string

concatenation operator+ (e.g., s1.concat(s2) is the same as s1+s2).fromCharCode(

value1, value2, )Converts a list of Unicode values into a string containing the corresponding

characters.indexOf(

substring, index )Searches for the first occurrence ofsubstringstarting from position index in

the string that invokes the method. The method returns the starting index ofsubstringin the source string or1 ifsubstringis not found. If the index

argument is not provided, the method begins searching from index 0 in thesource string.

lastIndexOf(substring, index )

Searches for the last occurrence ofsubstringstarting from position index andsearching toward the beginning of the string that invokes the method. The

method returns the starting index ofsubstringin the source string or1 if

substringis not found. If the index argument is not provided, the method

begins searching from the end of the source string.


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Methods of the String Object

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Methods that generate

XHTML tagsanchor( name ) Wraps the source string in an anchor element

() with name as the anchor name.blink() Wraps the source string in a

element.

fixed() Wraps the source string in a element.

link( url ) Wraps the source string in an anchor element() with urlas the hyperlink location.

strike() Wraps the source string in a element.

sub()Wraps the source string in a element.

sup() Wraps the source string in a element.


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String.substring() Method

The String.substring()method returns a sub-string of characters beginning at a specifiedindex and ending at a specified index. We

supply the beginning and ending indexes asarguments, separated with a comma.

While the method includes the beginning indexas part of the returned substring, it does NOTinclude the ending index.

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JavaScript substring() Method

The substring() method extracts the characters

from a string, between two specified indices,

and returns the new sub string.

This method extracts the characters in a string

between "from" and "to", not including "to"

itself.

Syntax

string.substring(from, to)

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Example

Extract characters from a string:

var str="Hello world!";

document.write(str.substring(3)+"
");

document.write(str.substring(3,7));

The output of the code above will be:

lo world!lo w


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JavaScript Regular Expressions

Regular expressions are patterns used to match

character combinations in strings. In

JavaScript, regular expressions are also

objects. These patterns are used with

the exec and test methods ofRegExp, and with

the match, replace, search, and splitmethods

ofString. This chapter describes JavaScriptregular expressions.

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https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/RegExp/exechttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/RegExp/testhttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/RegExphttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String/matchhttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String/replacehttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String/searchhttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String/splithttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Stringhttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Stringhttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String/splithttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String/searchhttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String/searchhttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String/replacehttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String/matchhttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/RegExphttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/RegExphttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/RegExp/testhttps://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/RegExp/exec


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Creating a Regular Expression

Syntax

var patt=new RegExp(pattern,modifiers)

or more simply:

var patt=/pattern/modifiers;

pattern specifies the pattern of an expression

modifiers specify if a search should be global,

case-sensitive, etc. JavaScript 18


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RegExp Object Methods

1.compile()- Compiles a regular expression

2.exec() -Tests for a match in a string.

Returns the first match

3.test() - Tests for a match in a string.

Returns true or false

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EXAMPLE OF REGULAR

EXPRESSION

var str = "Visit W3Schools"; var patt1 = /w3schools/i;

document.write(str.match(patt1));

output - W3Schools

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javascript strings object

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