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最新推荐文章于 2025-01-14 19:02:57 发布

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最新推荐文章于 2025-01-14 19:02:57 发布

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分类专栏： web design 文章标签： javascript object radiobutton methods properties date

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JavaScript的对象

The following objects are available in JavaScript:

NOTE: Each object topic indicates whether the object is part of the client (in Navigator), server (in LiveWire), or is common (built-in to JavaScript). Server objects are not included in this version of the documentation.

anchor object (client)

An anchor is a piece of text identified as the target of a hypertext link.

Syntax

To define an anchor, use standard HTML syntax :

<A NAME="anchorName"
   anchorText
</A>

NAME specifies a tag that becomes an available hypertext target within the current document.
anchorText specifies the text to display at the anchor.

Description

You can reference the anchor objects in your code by using the anchors property of the document object. The anchors property is an array that contains an entry for each anchor in a document.

xxx to be supplied

Properties

xxx to be supplied
Methods

xxx to be supplied

Event handlers

None.

Examples

   &amp;amp;lt;A NAME=&amp;amp;quot;javascript_intro&amp;amp;quot;&amp;amp;gt;&amp;amp;lt;H2&amp;amp;gt;Welcome to JavaScript&amp;amp;lt;/H2&amp;amp;gt;&amp;amp;lt;/A&amp;amp;gt;

Examples

A custom button does not necessarily load a new page into the client; it merely executes the script specified by the onClick event handler. In the following example, myfunction() is a JavaScript function.

   &amp;amp;lt;INPUT TYPE=&amp;amp;quot;button&amp;amp;quot; VALUE=&amp;amp;quot;Calculate&amp;amp;quot; NAME=&amp;amp;quot;calc_button&amp;amp;quot; onClick=&amp;amp;quot;myfunction(this.form)&amp;amp;quot;&amp;amp;gt;

Examples

   &amp;amp;lt;B&amp;amp;gt;Specify your music preferences (check all that apply):&amp;amp;lt;/B&amp;amp;gt; &amp;amp;lt;BR&amp;amp;gt;&amp;amp;lt;INPUT TYPE=&amp;amp;quot;checkbox&amp;amp;quot; NAME=&amp;amp;quot;musicpref_rnb&amp;amp;quot; CHECKED&amp;amp;gt; R&amp;amp;amp;B &amp;amp;lt;BR&amp;amp;gt;&amp;amp;lt;INPUT TYPE=&amp;amp;quot;checkbox&amp;amp;quot; NAME=&amp;amp;quot;musicpref_jazz&amp;amp;quot; CHECKED&amp;amp;gt; Jazz &amp;amp;lt;BR&amp;amp;gt;&amp;amp;lt;INPUT TYPE=&amp;amp;quot;checkbox&amp;amp;quot; NAME=&amp;amp;quot;musicpref_blues&amp;amp;quot; CHECKED&amp;amp;gt; Blues &amp;amp;lt;BR&amp;amp;gt;&amp;amp;lt;INPUT TYPE=&amp;amp;quot;checkbox&amp;amp;quot; NAME=&amp;amp;quot;musicpref_newage&amp;amp;quot; CHECKED&amp;amp;gt; New Age

Examples

The following example creates a hypertext link to an anchor named javascript_intro.

   &amp;amp;lt;A HREF=&amp;amp;quot;#javascript_intro&amp;amp;quot;&amp;amp;gt;Introduction to JavaScript&amp;amp;lt;/A&amp;amp;gt;

The following example creates a hypertext link to a URL.

   &amp;amp;lt;A HREF=&amp;amp;quot;http://www.netscape.com&amp;amp;quot;&amp;amp;gt;Netscape Home Page&amp;amp;lt;/A&amp;amp;gt;

Event handlers

None.

Examples

   &amp;amp;lt;B&amp;amp;gt;Password:&amp;amp;lt;/B&amp;amp;gt; &amp;amp;lt;INPUT TYPE=&amp;amp;quot;password&amp;amp;quot; NAME=&amp;amp;quot;password&amp;amp;quot; VALUE=&amp;amp;quot;&amp;amp;quot; SIZE=25&amp;amp;gt;

Examples

The following example defines a radio button group to choose among three catalogs. Each radio button is given the same name, NAME="choice", forming a group of buttons for which only one choice can be selected. The example also defines a text field that defaults to what was chosen via the radio buttons but that allows the user to type a nonstandard catalog name as well. JavaScript automatically sets the catalog name input field based on the radio buttons.

   &amp;amp;lt;INPUT TYPE=&amp;amp;quot;text&amp;amp;quot; NAME=&amp;amp;quot;catalog&amp;amp;quot; SIZE=&amp;amp;quot;20&amp;amp;quot;&amp;amp;gt; &amp;amp;lt;INPUT TYPE=&amp;amp;quot;radio&amp;amp;quot; NAME=&amp;amp;quot;choice&amp;amp;quot; VALUE=&amp;amp;quot;PRICEY&amp;amp;quot; onClick=&amp;amp;quot;form.catalog.value = 'top-of-the-line'&amp;amp;quot;&amp;amp;gt; It's really great! &amp;amp;lt;INPUT TYPE=&amp;amp;quot;radio&amp;amp;quot; NAME=&amp;amp;quot;choice&amp;amp;quot; VALUE=&amp;amp;quot;MODEST&amp;amp;quot; onClick=&amp;amp;quot;form.catalog.value = 'middle-of-the-road'&amp;amp;quot;&amp;amp;gt; It's pretty good. &amp;amp;lt;INPUT TYPE=&amp;amp;quot;radio&amp;amp;quot; NAME=&amp;amp;quot;choice&amp;amp;quot; VALUE=&amp;amp;quot;CHEAPO&amp;amp;quot; onClick=&amp;amp;quot;form.catalog.value = 'bargain-basement'&amp;amp;quot;&amp;amp;gt; It stinks!

Examples

The following example displays a text object containing "CA". If the user types a different state abbreviation in the text object and then clicks the Clear Form button, the original value of "CA" is restored.

   &amp;amp;lt;B&amp;amp;gt;State: &amp;amp;lt;/B&amp;amp;gt;&amp;amp;lt;INPUT TYPE=&amp;amp;quot;text&amp;amp;quot; NAME=&amp;amp;quot;state&amp;amp;quot; VALUE=&amp;amp;quot;CA&amp;amp;quot; SIZE=&amp;amp;quot;2&amp;amp;quot;&amp;amp;gt; &amp;amp;lt;P&amp;amp;gt;&amp;amp;lt;INPUT TYPE=&amp;amp;quot;reset&amp;amp;quot; VALUE=&amp;amp;quot;Clear Form&amp;amp;quot;&amp;amp;gt;

Examples

The following example displays a selection list.

   Choose the music type for your free CD: &amp;amp;lt;SELECT NAME=&amp;amp;quot;music_type_single&amp;amp;quot;&amp;amp;gt; &amp;amp;lt;OPTION SELECTED&amp;amp;gt; R&amp;amp;amp;B &amp;amp;lt;OPTION&amp;amp;gt; Jazz &amp;amp;lt;OPTION&amp;amp;gt; Blues &amp;amp;lt;OPTION&amp;amp;gt; New Age&amp;amp;lt;/SELECT&amp;amp;gt; &amp;amp;lt;P&amp;amp;gt;Choose the music types for your free CDs: &amp;amp;lt;BR&amp;amp;gt;&amp;amp;lt;SELECT NAME=&amp;amp;quot;music_type_multi&amp;amp;quot; MULTIPLE&amp;amp;gt; &amp;amp;lt;OPTION SELECTED&amp;amp;gt; R&amp;amp;amp;B &amp;amp;lt;OPTION&amp;amp;gt; Jazz &amp;amp;lt;OPTION&amp;amp;gt; Blues &amp;amp;lt;OPTION&amp;amp;gt; New Age&amp;amp;lt;/SELECT&amp;amp;gt;

Examples

   &amp;amp;lt;INPUT TYPE=&amp;amp;quot;submit&amp;amp;quot; NAME=&amp;amp;quot;submit_button&amp;amp;quot; VALUE=&amp;amp;quot;Done&amp;amp;quot;&amp;amp;gt;

Examples

   &amp;amp;lt;B&amp;amp;gt;Last name:&amp;amp;lt;/B&amp;amp;gt; &amp;amp;lt;INPUT TYPE=&amp;amp;quot;text&amp;amp;quot; NAME=&amp;amp;quot;last_name&amp;amp;quot; VALUE=&amp;amp;quot;&amp;amp;quot; SIZE=25&amp;amp;gt;

Examples

   &amp;amp;lt;B&amp;amp;gt;Description:&amp;amp;lt;/B&amp;amp;gt; &amp;amp;lt;BR&amp;amp;gt;&amp;amp;lt;TEXTAREA NAME=&amp;amp;quot;item_description&amp;amp;quot; ROWS=6 COLS=55&amp;amp;gt; Our storage ottoman provides an attractive way to store lots of CDs and videos--and it's versatile enough to store other things as well. It can hold up to 72 CDs under the lid and 20 videos in the drawer below. &amp;amp;lt;/TEXTAREA&amp;amp;gt;

   &amp;amp;lt;FORM NAME=&amp;amp;quot;myform&amp;amp;quot;&amp;amp;gt; &amp;amp;lt;INPUT TYPE=&amp;amp;quot;button&amp;amp;quot; NAME=&amp;amp;quot;Button1&amp;amp;quot; VALUE=&amp;amp;quot;Open Sesame!&amp;amp;quot; onClick=&amp;amp;quot;window.open('sesame.html', 'newWin', 'toolbar=no,directories=no,menubar=no,status=yes,width=300,height=300')&amp;amp;quot;&amp;amp;gt; &amp;amp;lt;/form&amp;amp;gt;

Notice the use of single quotes (') inside the onClick event handler.

Syntax

1. // comment text 
2. /* multiple line comment text */

Examples

// This is a single-line comment.


/* This is a multiple-line comment. It can be of any length, and 
you can put whatever you want here. */

continue statement

The continue statement terminates execution of the block of statements in a while or for loop, and continues execution of the loop with the next iteration. In contrast to the break statement, it does not terminate the execution of the loop entirely: instead,

In a while loop it jumps back to the condition.
In a for loop it jumps to the update expression.

Syntax

continueExamples
The following example shows a while loop that has a continue statement that executes when the value of i is 3. Thus, n takes on the values 1, 3, 7, and 12. 
 
i = 0; 
n = 0; 
while (i < 5) { 
    i++; 
    if (i == 3) 
        continue;  
    n += i;
} 

    
  
  

    for statement
    
    A for loop consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a block of statements executed in the loop. The parts of the for statement are: 
    
  
  The initial expression, generally used to initialize a counter variable. This statement may optionally declare new variables with the var keyword. This expression is optional. 
The condition that is is evaluated on each pass through the loop. If this condition is true, the statements in the succeeding block are performed. This conditional test is optional. If omitted, then the condition always evaluates to true. 
An update expression generally used to update or increment the counter variable. This expression is optional. 
A block of statements that are executed as long as the condition is true. This can be a single statement or multiple statements. Although not required, it is good practice to indent these statements four spaces from the beginning of the for statement. 
    Syntax
    for ([initial expression]; [condition]; [update expression]) {
    statements
}
initial expression = statement | variable declartion

    Examples
    This simple for statement starts by declaring the variable i and initializing it to zero. It checks that i is less than nine, and performs the two succeeding statements, and increments i by one after each pass through the loop. 
    for (var i = 0; i < 9; i++) { 
    n += i;
    myfunc(n);
}

    
  
  

    for...in statement
    
    The for statement iterates variable var over all the properties of object obj. For each distinct property, it executes the statements in statements. 
    Syntax
    for (var in obj) { 
    statements }
    Examples
    The following function takes as its argument an object and the object's name. It then iterates over all the object's properties and returns a string that lists the property names and their values. 
    function dump_props(obj, obj_name) { 
    var result = "", i = "";
    for (i in obj)
        result += obj_name + "." + i + " = " + obj[i] + "/n";
    return result;
} 
    
  
  

    function statement
    
    The function statement declares a JavaScript function name with the specified parameters param. To return a value, the function must have a return statement that specifies the value to return. You cannot nest a function statement in another statement or in itself. 
    All parameters are passed to functions, by value. In other words, the value is passed to the function, but if the function changes the value of the parameter, this change is not reflected globally or in the calling function. 
    Syntax
    function name([param] [, param] [..., param]) {
    statements }
    Examples
    //This function returns the total dollar amount of sales, when 
//given the number of units sold of products a, b, and c.
function calc_sales(units_a, units_b, units_c) {
    return units_a*79 + units_b*129 + units_c*699
}
    
  
  

    if...else statement
    
    The if...else statement is a conditional statement that executes the statements in statements if condition is true. In the optional else clause, it executes the statements in else statements if condition is false. These may be any JavaScript statements, including further nested if statements. 
    Syntax
    if (condition) {
    statements
} [else {
    else statements
}]
    Examples
    if ( cipher_char == from_char ) {
    result = result + to_char; 
    x++
} else  
    result = result + clear_char; 
 
    
  
  

    return statement
    
    The return statement specifies the value to be returned by a function. 
    Syntax
    return expression;
    Examples
    The following simple function returns the square of its argument, x, where x is an number. 
    function square( x ) { 
    return x * x; 
} 
    
  
  

    var statement
    
    The var statement declares a variable varname, optionally initializing it to have value. The variable name varname can be any legal identifier, and value can be any legal expression. The scope of a variable is the current function or, for variables declared outside a function, the current application. 
    Using var outside a function is optional; you can declare a variable by simply assigning it a value. However, it is good style to use var, and it is neccessary in functions if there is a global variable of the same name. So, in general, it is a good idea to always use var, but you should definitely use it when declaring a local variable in a function, to ensure that any global variable of the same name does not override it. 
    Syntax
    var varname [= value] [..., varname [= value] ]

    Examples
    var num_hits = 0, cust_no = 0 
    
  
  

    while statement
    
    The while statement is a loop that evaluates the expression condition,and if it is true, executes statements. It then repeats this process, as long as condition is true. When condition evaluates to false, execution continues with the next statement following the statements. 
    Although not required, it is good practice to indent the statements a while loop four spaces from the beginning of the for statement. 
    Syntax
    while (condition) {
    statements
}

    Examples
    The following simple while loop iterates as long as n is less than three. Each iteration, it increments n and adds it to x. Therefore, x and n take on the following values 
    
  
  After first pass: x = 1 and n = 1 
After second pass: x = 2 and n = 3 
After third pass: x = 3 and n = 6 
    After completing the third pass, the condition n < 3 is no longer true, so the loop terminates. 
    n = 0; 
x = 0; 
while( n < 3 ) { 
    n ++; x += n; 
} 
    
  
  

    with statement
    
    The with statement establishes object as the default object for the statements. Any property references without an object are then assumed to be for object. Note that the parentheses are required around object. 
    Syntax
    with (object){ 
     statements 
}
    Examples
    with (Math) { 
    a = PI * r*r
    x = r * cos(theta)
    y = r * sin(theta) 
}