stmt.html

javascript 1.5规范

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<A NAME="Examples"> </A>
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<zrefheader>Examples</zrefheader>
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<A NAME="1004813"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>The following <FONT FACE="courier, couriernew, monospaced size">for</FONT> statement starts by declaring the variable <FONT FACE="courier, couriernew, monospaced size">i</FONT> and initializing it to 0. It checks that <FONT FACE="courier, couriernew, monospaced size">i</FONT> is less than nine, performs the two succeeding statements, and increments <FONT FACE="courier, couriernew, monospaced size">i</FONT> by 1 after each pass through the loop.</zparagraph>
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<A NAME="1004814"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2">
<zcodeline>for (var i = 0; i &lt; 9; i++) {<br>
&nbsp;&nbsp;&nbsp;n += i;<br>
&nbsp;&nbsp;&nbsp;myfunc(n);<br>
}
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<A NAME="1004815"> </A>
<A NAME="for...in"> </A>
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<zhead1>for...in</zhead1>
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<A NAME="1004816"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>Iterates a specified variable over all the properties of an object. For each distinct property, JavaScript executes the specified statements.<BR>
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<ztabletext><I>Implemented in</I></ztabletext>
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<A NAME="1041898"> </A>
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<ztabletext>JavaScript 1.0, NES 2.0</ztabletext>
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<A NAME="1050148"> </A>
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<ztabletext><I>ECMA version</I></ztabletext>
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<A NAME="1050150"> </A>
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<ztabletext>ECMA-262</ztabletext>
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<A NAME="Syntax"> </A>
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<zrefheader>Syntax</zrefheader>
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<A NAME="1004818"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2">
<zcodeline>for (<I>variable</I> in <I>object</I>) {<br>
&nbsp;&nbsp;&nbsp;<I>statements<br>
</I>}
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<A NAME="1005653"> </A>
<A NAME="Parameters"> </A>
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<zrefheader>Parameters</zrefheader>
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<A NAME="1004819"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph><BR>
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<zcodeline>variable
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<ztabletext>Variable to iterate over every property, optionally declared with the <FONT FACE="courier, couriernew, monospaced size">var</FONT> keyword. This variable is local to the function, not to the loop.</ztabletext>
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<zcodeline>object
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<A NAME="1012768"> </A>
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<ztabletext>Object for which the properties are iterated.</ztabletext>
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<zcodeline>statements
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<A NAME="1012792"> </A>
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<ztabletext>Specifies the statements to execute for each property.</ztabletext>
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<A NAME="1004822"> </A>
<A NAME="Examples"> </A>
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<zrefheader>Examples</zrefheader>
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<A NAME="1004823"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>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.</zparagraph>
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<A NAME="1004824"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2">
<zcodeline>function show_props(obj, objName) {<br>
&nbsp;&nbsp;&nbsp;var result = "";<br>
&nbsp;&nbsp;&nbsp;for (var i in obj) {<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;result += objName + "." + i + " = " + obj[i] + "\n";<br>
&nbsp;&nbsp;&nbsp;}<br>
&nbsp;&nbsp;&nbsp;return result;<br>
}
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<A NAME="1004825"> </A>
<A NAME="function"> </A>
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<zhead1>function</zhead1>
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<A NAME="1004826"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>Declares a function with the specified parameters. Acceptable parameters include strings, numbers, and objects.<BR>
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<A NAME="1035950"> </A>
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<ztabletext><I>Implemented in</I></ztabletext>
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<A NAME="1041939"> </A>
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<ztabletext>JavaScript 1.0, NES 2.0</ztabletext>
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<A NAME="1076881"> </A>
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<ztabletext></ztabletext>
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<A NAME="1076898"> </A>
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<ztabletext>JavaScript 1.5, NES 6.0: added conditional function declarations (Netscape extension).</ztabletext>
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<A NAME="1050161"> </A>
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<ztabletext><I>ECMA version</I></ztabletext>
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<A NAME="1050163"> </A>
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<ztabletext>ECMA-262</ztabletext>
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<A NAME="1004829"> </A>
<A NAME="Syntax"> </A>
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<zrefheader>Syntax</zrefheader>
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<A NAME="1004830"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2">
<zcodeline>function <I>name</I>([<I>param</I>] [, <I>param</I>] [..., <I>param</I>]) {<br>
&nbsp;&nbsp;&nbsp;<I>statements<br>
</I>}
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<A NAME="1065583"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>You can also define functions using the <A HREF="function.html#1193137"  >Function</A> constructor and the <A HREF="ops.html#1066344"  >function</A> operator; see <A HREF="function.html#1193137"  >Function</A> and <A HREF="ops.html#1066344"  >function</A>.</zparagraph>
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<A NAME="1007886"> </A>
<A NAME="Parameters"> </A>
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<zrefheader>Parameters</zrefheader>
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<A NAME="1007887"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph><BR>
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<zcodeline>name
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<A NAME="1012965"> </A>
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<ztabletext>The function name.</ztabletext>
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<zcodeline>param
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<A NAME="1013010"> </A>
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<ztabletext>The name of an argument to be passed to the function. A function can have up to 255 arguments.</ztabletext>
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<zcodeline>statements
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<A NAME="1074667"> </A>
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<ztabletext>The statements which comprise the body of the function.</ztabletext>
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<A NAME="1008195"> </A>
<A NAME="Description"> </A>
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<zrefheader>Description</zrefheader>
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<A NAME="1065101"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>To return a value, the function must have a <A HREF="stmt.html#1004871"  >return</A> statement that specifies the value to return.</zparagraph>
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<A NAME="1071423"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>A function created with the <FONT FACE="courier, couriernew, monospaced size">function</FONT> statement is a <FONT FACE="courier, couriernew, monospaced size">Function</FONT> object and has all the properties, methods, and behavior of <FONT FACE="courier, couriernew, monospaced size">Function</FONT> objects. See <A HREF="function.html#1193137"  >Function</A> for detailed information on functions.</zparagraph>
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<A NAME="1076846"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>Netscape supports conditional function declarations, whereby a function can be declared based on the evaluation of a condition. If the condition evaluates to true, the function is declared. Otherwise it is not declared.</zparagraph>
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<A NAME="1083248"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>A function can also be declared inside an expression. In this case the function is usually anonymous. See <A HREF="ops.html#1066344"  >page&nbsp;254</A>.</zparagraph>
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<A NAME="1004831"> </A>
<A NAME="Examples"> </A>
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<zrefheader>Examples</zrefheader>
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<A NAME="1004832"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>The following code declares a function that returns the total dollar amount of sales, when given the number of units sold of products a, b, and c.</zparagraph>
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<A NAME="1079065"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2">
<zcodeline>function calc_sales(units_a, units_b, units_c) {<br>
&nbsp;&nbsp;&nbsp;return units_a*79 + units_b*129 + units_c*699<br>
}
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<A NAME="1079066"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>In the following script, the one function is always declared. The zero function is declared because '<FONT FACE="courier, couriernew, monospaced size">if(1)'</FONT> evaluates to true:</zparagraph>
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<A NAME="1079067"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2">
<zcodeline>&lt;SCRIPT language="JavaScript1.5"&gt;<br>
&lt;!--<br>
function one()<br>
&nbsp;&nbsp;&nbsp;document.writeln("This is one.");<br>
&nbsp;&nbsp;&nbsp;if (1)<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;function zero()<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;document.writeln("This is zero.");<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<br>
}<br>
&lt;/SCRIPT&gt;
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<A NAME="1077232"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>However, if the script is changed so that the condition becomes '<FONT FACE="courier, couriernew, monospaced size">if (0)'</FONT>, function zero is not declared and cannot be invoked on the page.</zparagraph>
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<A NAME="1065517"> </A>
<A NAME="See also"> </A>
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<zrefheader>See also</zrefheader>
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<A NAME="1065521"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph><A HREF="function.html#1193137"  >Function</A>, <A HREF="ops.html#1066344"  >function</A></zparagraph>
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<A NAME="1004833"> </A>
<A NAME="if...else"> </A>
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<zhead1>if...else</zhead1>
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<A NAME="1004834"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>Executes a set of statements if a specified condition is true. If the condition is false, another set of statements can be executed.<BR>
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