7. Built-in Objects
JavaScript includes a number of built-in objects that assist developers in manipulating certain data types inlcuding, most notably: dates, arrays, strings and numbers.
Date() The JavaScript Date object is used to work with dates and time
Array() The JavaScript Array object is used to work with arrays of values and objects
String The JavaScript String object is used to manipulate strings of character data
Math The JavaScript Math object is used to calculate number values
7.1 Date()
The JavaScript Date object is used to work with dates and time
7.1.1 Syntax
An instance of the date object is created when it is assigned to a variable using the reserved words new
var variable-label=new Date([optional arguments])
The optional-arguments are one of several valid date time expressions.
If no arguments are passed, the instance of Date() is initialized to local time:
var now=new Date()
7.1.1.1 Date By Calendar Terms
The instance of date can be assigned to a specific calendar date and time by including integers representing optionally, with increasing precision, from left to right:
var variable = new Date(year,month,date[,hours[,minutes[,seconds[,ms]]]])
year is a two or four digit representation of the year, month is an integer between 0 and 11 representing the order the month, and date is an integer between 1 and 31 representing the day of the month:
var variable=new Date(2001,0,1) // Jan 1, 2001
var variable=new Date(88,11,1,16) // Dec 1, 1988 4:00 pm
7.1.1.2 Date By Date String
The date object can be initialized to a particular date and time using one of several recognized quoted date string formats:
var variable=new Date("[datestring]")
var then=new Date("January 1, 2001")
var laterThatDay=new Date("January 1, 2001 12:24:00")
7.1.1.2 Date By Milleseconds
In addition, Date() can assigned to a specifice date and time using a thirteen term number value representing the number of milliseconds since Jan 1, 1970 00:00:00:
var variable=new Date(NNNNNNNNNNNNN)
var now=new Date() // current time
Note that this method is most useful in calculating relative dates. There are for instance 86400000 milliseconds in a calendar day (see Listing 7.1 below)
7.1.2 Properties
None
7.1.3 Methods
| Date() | Returns a Date object
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| getDate() | Returns the date of a Date object (from 1-31)
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| getDay() | Returns the day of a Date object (from 0-6)
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| getMonth() | Returns the month of a Date object (from 0-11)
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| getFullYear() | Returns the year of a Date object (four digits)
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| getYear() | Returns the year of a Date object (from 0-99)
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| getHours() | Returns the hour of a Date object (from 0-23)
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| getMinutes() | Returns the minute of a Date object (from 0-59)
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| getSeconds() | Returns the second of a Date object (from 0-59)
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| getMilliseconds() | Returns the millisecond of a Date object (from 0-999)
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| getTime() | Returns the number of milliseconds since midnight 1/1-1970
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| getTimezoneOffset() | Returns the time difference between the user's computer and GMT
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| getUTCDate() | Returns the date of a Date object in universal (UTC) time
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| getUTCDay() | Returns the day of a Date object in universal time
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| getUTCMonth() | Returns the month of a Date object in universal time
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| getUTCFullYear() | Returns the four-digit year of a Date object in universal time
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| getUTCHours() | Returns the hour of a Date object in universal time
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| getUTCMinutes() | Returns the minutes of a Date object in universal time
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| getUTCSeconds() | Returns the seconds of a Date object in universal time
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| getUTCMilliseconds() | Returns the milliseconds of a Date object in universal time
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| toGMTString() | Converts the Date object to a string, set to GMT time zone
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| toLocaleString() | Converts the Date object to a string, set to the current time zone
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| toString() | Converts the Date object to a string
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Listing 7.1 Date()
var now=new Date();
function days_to_ms(n) {
return(n*86400000);
}
for(i=0;i<7;i++) {
then = new Date( now.getTime() + days_to_ms(i) );
document.write("<p>" + then.toLocaleString());
document.write("<li>getDate: " + then.getDate());
document.write("<li>getDay: " + then.getDay());
document.write("<li>getMonth: " + then.getMonth());
document.write("<li>getYear: " + then.getYear());
document.write("<li>getFullYear: " + then.getFullYear());
document.write("</p>");
}
7.2 Array()
The JavaScript Array object is used to work with arrays of values and objects
Syntax for creating indexed arrays was provided in Part 3 JavaScript Arrays along with examples of the sort() and reverse() methods. This listing reviews those basics and adds several additional widely supported methods.
7.2.2 Syntax
An instance of an array object is created using the key words new and Array()
var variable = new Array();
The developer may define initial members of the array as comma separated list of values included in the parenthesis of the Array() declaration:
var variable = new Array([value[,value[,value]]]);
The developer can declare an empty prototype to which members are later assigned using an indexed based syntax variable[n]=[value]:
var variable = new Array();
variable[0]=[value];
variable[1]=[value];
variable[2]=[value];
7.2.2 Properties
| length | Returns the number of members in the array
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7.2.3 Methods
| concat() | Return two or more arrays as a new array
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| join([delimiter]) | Joins the elements of an array into a string separated by specified [delimiter]
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| reverse() | Reverses the order of the elements in an array
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| slice(x[,y]) | Creates a new array from section x-y of an existing array
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| sort() | Sorts the elements of an array from A-Z
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| toSource() | Returns a string that represents the source code of the array
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| toString() | Returns a string that represents the specified array and its elements
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Listing 7.2 Array()
var students1=new Array("Jane","Tom","Mary","Anne","Ahmed");
var students2=new Array("Lisa","John","Mark","Karen","Pilar");
students1=students1.sort()
document.write("<p>"+students1.join(', '));
students1=students1.reverse()
document.write("<p>"+students1.join(', '));
var students_all=students1.concat(students2).sort();
document.write("<p>"+students_all.join(', '));
students_all=students_all.slice(0,3);
document.write("<p>"+students_all.join(', '));
7.3 String
The JavaScript String object is used to manipulate strings of character data
7.3.1 Syntax
String type data is initially assigned to a variable in the form of a quoted literal using a matched pair of either double or sing quotes ("[value]") ('[value]')
var variable="[cdata]";
var variable='[cdata]';
Single quotes may appear within double quotes (" 'example' ") and vice versa (' "example" ')
var variable="Say 'good night', Mary";
var variable='Say "good night", Mary';
Both single and double quotes can be escaped using the backslash (" \"example\" ") (' \'example\' ')
var variable="Say \"good night\", Mary";
var variable='Say \'good night\', Mary';
7.3.2 Properties
| length | Returns the number of characters in the string
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7.3.2 Methods
|
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| anchor() | Returns a string as an anchor |
| big() | Returns a string in big text |
| bold() | Returns a string in bold |
| charAt(index) | Returns the character at a specified position |
| charCodeAt(i) | Returns the Unicode of the character at a specified position |
| concat() | Returns two concatenated strings |
| fixed() | Returns a string as monospace text |
| fontcolor() | Returns a string in a specified color |
| fontsize() | Returns a string in a specified size |
| fromCharCode() | Returns the character value of a Unicode |
| indexOf() | Returns the first index of the specified characters, or -1 if unmatched |
| italics() | Returns a string in italic |
| lastIndexOf() | Returns the last index of the specified characters, or -1 if unmatched |
| link() | Returns a string as a hyperlink |
| match() | Returns the first index of the specified characters, or null if unmatched |
| replace() | Replaces some specified characters with some new specified characters |
| search() | Returns the index of the specified characters, or -1 if unmatched |
| slice() | Returns a string containing a specified character index |
| small() | Returns a string as small text |
| split() | Splits a string into an array of strings |
| strike() | Returns a string strikethrough |
| sub() | Returns a string as subscript |
| substr() | Returns the specified characters. |
| substring() | Returns the specified characters. |
| sup() | Returns a string as superscript |
| toLowerCase() | Converts a string to lower case |
| toUpperCase() | Converts a string to upper case |
Listing 7.2 String
var string_1="Text String";
document.write("<p>" + string_1.big())
document.write("<p>" + string_1.bold())
document.write("<p>" + string_1.fixed())
document.write("<p>" + string_1.fontcolor('red'))
document.write("<p>" + string_1.fontsize('3'))
document.write("<p>" + string_1.italics())
document.write("<p>" + string_1.link('#'))
document.write("<p>" + string_1.small())
document.write("<p>" + string_1.strike())
document.write("<p>" + string_1.sub())
document.write("<p>" + string_1.sup())
document.write("<p>" + string_1.toLowerCase())
document.write("<p>" + string_1.toUpperCase())
7.4 Math
The JavaScript Math object is used to calculate number values
7.4.1 Properties
none
7.4.2 Methods
| abs(x) | Returns the absolute value of x |
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| acos(x) | Returns the arccosine of x |
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| asin(x) | Returns the arcsine of x |
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| atan(x) | Returns the arctangent of x |
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| atan2(y,x) | Returns the angle from the x axis to a point |
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| ceil(x) | Returns the nearest integer greater than or equal to x |
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| cos(x) | Returns the cosine of x |
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| exp(x) | Returns the value of E raised to the power of x |
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| floor(x) | Returns the nearest integer less than or equal to x |
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| log(x) | Returns the natural log of x |
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| max(x,y) | Returns the number with the highest value of x and y |
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| min(x,y) | Returns the number with the lowest value of x and y |
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| pow(x,y) | Returns the value of the number x raised to the power of y |
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| random() | Returns a random number between 0 and 1 |
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| round(x) | Rounds x to the nearest integer |
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| sin(x) | Returns the sine of x |
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| sqrt(x) | Returns the square root of x |
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| tan(x) | Returns the tangent of x |
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