?? toplev.html
字號:
<BR> <TR> <TD VALIGN=TOP><P><A NAME="1063966"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext><I>Core property</I></ztabletext></FONT> </TD> <TD VALIGN=TOP><P><A NAME="1063968"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext></ztabletext></FONT> </TD> </TR> <TR> <TD VALIGN=TOP><P><A NAME="1063970"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext><I>Implemented in</I></ztabletext></FONT> </TD> <TD VALIGN=TOP><P><A NAME="1063972"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext>JavaScript 1.3 (In previous versions, <FONT FACE="courier, couriernew, monospaced size">Infinity</FONT> was defined only as a property of the <FONT FACE="courier, couriernew, monospaced size">Number</FONT> object.)</ztabletext></FONT> </TD> </TR> <TR> <TD VALIGN=TOP><P><A NAME="1074319"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext><I>ECMA version</I></ztabletext></FONT> </TD> <TD VALIGN=TOP><P><A NAME="1074321"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext>ECMA-262</ztabletext></FONT> </TD> </TR></TABLE><P></zparagraph></FONT><P><BR><A NAME="1063974"> </A><A NAME="Syntax"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><B><zrefheader>Syntax</zrefheader></B></FONT><BR><A NAME="1063975"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2"><zcodeline>Infinity</zcodeline></FONT><P><BR><A NAME="1063976"> </A><A NAME="Description"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><B><zrefheader>Description</zrefheader></B></FONT><BR><A NAME="1063977"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph><FONT FACE="courier, couriernew, monospaced size">Infinity</FONT> is a top-level property and is not associated with any object.</zparagraph></FONT><P><A NAME="1097265"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>The initial value of <FONT FACE="courier, couriernew, monospaced size">Infinity</FONT> is <FONT FACE="courier, couriernew, monospaced size">Number.POSITIVE_INFINITY</FONT>. The value <FONT FACE="courier, couriernew, monospaced size">Infinity</FONT> (positive infinity) is greater than any other number including itself. This value behaves mathematically like infinity; for example, anything multiplied by <FONT FACE="courier, couriernew, monospaced size">Infinity</FONT> is <FONT FACE="courier, couriernew, monospaced size">Infinity</FONT>, and anything divided by <FONT FACE="courier, couriernew, monospaced size">Infinity</FONT> is 0.</zparagraph></FONT><P><BR><A NAME="1063978"> </A><A NAME="See also"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><B><zrefheader>See also</zrefheader></B></FONT><BR><A NAME="1063985"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph><A HREF="number.htm#1193346" >Number.NEGATIVE_INFINITY</A><FONT FACE="courier, couriernew, monospaced size">,</FONT><A HREF="number.htm#1193380" >Number.POSITIVE_INFINITY</A></zparagraph></FONT><P><BR><BR><A NAME="1063988"> </A><A NAME="isFinite"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="4"><zhead1>isFinite</zhead1><HR SIZE="2" NOSHADE></FONT><BR><A NAME="1063998"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>Evaluates an argument to determine whether it is a finite number.<BR><P><TABLE WIDTH="90%" BORDER="1" CELLPADDING="5" CELLSPACING="0"> <CAPTION></CAPTION><P><FONT FACE=""><B></B></FONT><BR><BR> <TR> <TD VALIGN=TOP><P><A NAME="1063991"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext><I>Core function</I></ztabletext></FONT> </TD> <TD VALIGN=TOP><P><A NAME="1063993"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext></ztabletext></FONT> </TD> </TR> <TR> <TD VALIGN=TOP><P><A NAME="1063995"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext><I>Implemented in</I></ztabletext></FONT> </TD> <TD VALIGN=TOP><P><A NAME="1063997"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext>JavaScript 1.3</ztabletext></FONT> </TD> </TR> <TR> <TD VALIGN=TOP><P><A NAME="1074336"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext><I>ECMA version</I></ztabletext></FONT> </TD> <TD VALIGN=TOP><P><A NAME="1074338"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext>ECMA-262</ztabletext></FONT> </TD> </TR></TABLE><P></zparagraph></FONT><P><BR><A NAME="1063999"> </A><A NAME="Syntax"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><B><zrefheader>Syntax</zrefheader></B></FONT><BR><A NAME="1064000"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2"><zcodeline>isFinite(<I>number</I>)</zcodeline></FONT><P><BR><A NAME="1064001"> </A><A NAME="Parameters"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><B><zrefheader>Parameters</zrefheader></B></FONT><BR><A NAME="1064007"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph><BR><P><TABLE WIDTH="90%" BORDER="1" CELLPADDING="5" CELLSPACING="0"> <CAPTION></CAPTION><P><FONT FACE=""><B></B></FONT><BR><BR> <TR> <TD VALIGN=TOP><A NAME="1064004"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2"><zcodeline>number</zcodeline></FONT><P> </TD> <TD VALIGN=TOP><P><A NAME="1064006"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext>The number to evaluate.</ztabletext></FONT> </TD> </TR></TABLE><P></zparagraph></FONT><P><BR><A NAME="1064008"> </A><A NAME="Description"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><B><zrefheader>Description</zrefheader></B></FONT><BR><A NAME="1097420"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph><FONT FACE="courier, couriernew, monospaced size">isFinite</FONT> is a top-level function and is not associated with any object.</zparagraph></FONT><P><A NAME="1097340"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>You can use this method to determine whether a number is a finite number. The <FONT FACE="courier, couriernew, monospaced size">isFinite</FONT> method examines the number in its argument. If the argument is <FONT FACE="courier, couriernew, monospaced size">NaN</FONT>, positive infinity or negative infinity, this method returns <FONT FACE="courier, couriernew, monospaced size">false</FONT>, otherwise it returns <FONT FACE="courier, couriernew, monospaced size">true</FONT>.</zparagraph></FONT><P><BR><A NAME="1073394"> </A><A NAME="Examples"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><B><zrefheader>Examples</zrefheader></B></FONT><BR><A NAME="1073395"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>You can check a client input to determine whether it is a finite number.</zparagraph></FONT><P><A NAME="1064013"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2"><zcodeline>if(isFinite(ClientInput) == true)<br>{<br> /* take specific steps */<br>}</zcodeline></FONT><P><BR><A NAME="1064014"> </A><A NAME="See also"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><B><zrefheader>See also</zrefheader></B></FONT><BR><A NAME="1064021"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph><A HREF="number.htm#1193346" >Number.NEGATIVE_INFINITY</A><FONT FACE="courier, couriernew, monospaced size">,</FONT><A HREF="number.htm#1193380" >Number.POSITIVE_INFINITY</A></zparagraph></FONT><P><BR><BR><A NAME="1064024"> </A><A NAME="isNaN"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="4"><zhead1>isNaN</zhead1><HR SIZE="2" NOSHADE></FONT><BR><A NAME="1064034"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>Evaluates an argument to determine if it is not a number.<BR><P><TABLE WIDTH="90%" BORDER="1" CELLPADDING="5" CELLSPACING="0"> <CAPTION></CAPTION><P><FONT FACE=""><B></B></FONT><BR><BR> <TR> <TD VALIGN=TOP><P><A NAME="1064027"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext><I>Core function</I></ztabletext></FONT> </TD> <TD VALIGN=TOP><P><A NAME="1064029"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext></ztabletext></FONT> </TD> </TR> <TR> <TD VALIGN=TOP><P><A NAME="1064031"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext><I>Implemented in</I></ztabletext></FONT> </TD> <TD VALIGN=TOP><P><A NAME="1064033"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext>JavaScript 1.0: Unix only</ztabletext></FONT><P><A NAME="1070173"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext></ztabletext></FONT><P><A NAME="1070174"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext>JavaScript 1.1, NES 2.0: all platforms</ztabletext></FONT> </TD> </TR> <TR> <TD VALIGN=TOP><P><A NAME="1074350"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext><I>ECMA version</I></ztabletext></FONT> </TD> <TD VALIGN=TOP><P><A NAME="1074352"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext>ECMA-262</ztabletext></FONT> </TD> </TR></TABLE><P></zparagraph></FONT><P><BR><A NAME="1064035"> </A><A NAME="Syntax"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><B><zrefheader>Syntax</zrefheader></B></FONT><BR><A NAME="1064036"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2"><zcodeline>isNaN(<I>testValue</I>)</zcodeline></FONT><P><BR><A NAME="1064037"> </A><A NAME="Parameters"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><B><zrefheader>Parameters</zrefheader></B></FONT><BR><A NAME="1064043"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph><BR><P><TABLE WIDTH="90%" BORDER="1" CELLPADDING="5" CELLSPACING="0"> <CAPTION></CAPTION><P><FONT FACE=""><B></B></FONT><BR><BR> <TR> <TD VALIGN=TOP><A NAME="1064040"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2"><zcodeline>testValue</zcodeline></FONT><P> </TD> <TD VALIGN=TOP><P><A NAME="1064042"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><ztabletext>The value you want to evaluate.</ztabletext></FONT> </TD> </TR></TABLE><P></zparagraph></FONT><P><BR><A NAME="1064044"> </A><A NAME="Description"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><B><zrefheader>Description</zrefheader></B></FONT><BR><A NAME="1097479"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph><FONT FACE="courier, couriernew, monospaced size">isNaN</FONT> is a top-level function and is not associated with any object.</zparagraph></FONT><P><A NAME="1064045"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>The <FONT FACE="courier, couriernew, monospaced size">parseFloat</FONT> and <FONT FACE="courier, couriernew, monospaced size">parseInt</FONT> functions return <FONT FACE="courier, couriernew, monospaced size">NaN</FONT> when they evaluate a value that is not a number. <FONT FACE="courier, couriernew, monospaced size">isNaN</FONT> returns true if passed <FONT FACE="courier, couriernew, monospaced size">NaN</FONT>, and false otherwise.</zparagraph></FONT><P><BR><A NAME="1064047"> </A><A NAME="Examples"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><B><zrefheader>Examples</zrefheader></B></FONT><BR><A NAME="1064048"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph>The following example evaluates <FONT FACE="courier, couriernew, monospaced size">floatValue</FONT> to determine if it is a number and then calls a procedure accordingly:</zparagraph></FONT><P><A NAME="1064049"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2"><zcodeline>floatValue=parseFloat(toFloat)</zcodeline></FONT><P><A NAME="1064050"></A><FONT FACE="courier, couriernew, monospaced size" SIZE="2"><zcodeline>if (isNaN(floatValue)) {<br> notFloat()<br>} else {<br> isFloat()<br>}</zcodeline></FONT><P><BR><A NAME="1064051"> </A><A NAME="See also"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><B><zrefheader>See also</zrefheader></B></FONT><BR><A NAME="1064061"> </A><FONT FACE="Arial, Helvetica, sans-serif" SIZE="2"><zparagraph><A HREF="number.htm#1193302" >Number.NaN</A>, <A HREF="toplev.htm#1064132" >parseFloat</A>, <A HREF="toplev.htm#1064173" >parseInt</A></zparagraph>?? 快捷鍵說明
復制代碼
Ctrl + C
搜索代碼
Ctrl + F
全屏模式
F11
切換主題
Ctrl + Shift + D
顯示快捷鍵
?
增大字號
Ctrl + =
減小字號
Ctrl + -