Download - 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
JavaScript String Object
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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JavaScript 5
JavaScript String Object
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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JavaScript 6
JavaScript String Object
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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JavaScript String Object
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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JavaScript String Object
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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JavaScript String Object
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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JavaScript String Object
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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JavaScript String Object
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 21