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<html><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Keywords" name="Keywords"content="JavaScript, examples, JavaScript: The Definitive Guide"><title>Example 3-2 from JavaScript: The Definitive Guide, Fifth Edition</title><style>body { font-family: arial, sans-serif}.lefttitle { font: bold x-small arial, sans-serif; margin: 5px; letter-spacing: .15em; text-transform:uppercase;}.leftcaption { font: italic x-small sans-serif; margin-bottom: 20px;}#banner { font-family:sans-serif; color:#333; font-size:x-large; font-weight:normal; padding:15px; padding-top: 3px; border-bottom:4px double #666;}#banner h1 { font-size: x-large; margin: 0px; padding: 0px;}#banner .description { font-size:large; margin-left: 2px;}pre { border: solid black 1px; background-color: #ddd; padding: 10px; margin: 0px;} </style></script></head><body><div id="banner"><h1>davidflanagan.com/javascript5</h1><span class="description">Example 3-2 from<i>JavaScript: The Definitive Guide, Fifth Edition</i></span></div><div style="float: left; 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text-align: right"><a href="index.html" tppabs="http://www.davidflanagan.com/javascript5/index.html">Table of Examples</a></div><pre>// Here we create an object representing the date of Christmas, 2007// The variable xmas contains a reference to the object, not the object itselfvar xmas = new Date(2007, 11, 25);// When we copy by reference, we get a new reference to the original objectvar solstice = xmas; // Both variables now refer to the same object value// Here we change the object through our new reference to itsolstice.setDate(21);// The change is visible through the original reference, as wellxmas.getDate(); // Returns 21, not the original value of 25// The same is true when objects and arrays are passed to functions.// The following function adds a value to each element of an array.// A reference to the array is passed to the function, not a copy of the array.// Therefore, the function can change the contents of the array through// the reference, and those changes will be visible when the function returns.function add_to_totals(totals, x){ totals[0] = totals[0] + x; totals[1] = totals[1] + x; totals[2] = totals[2] + x;}// Finally, we'll examine comparison by reference.// When we compare the two variables defined above, we find they are// equal, because they refer to the same object, even though we were trying// to make them refer to different dates:(xmas == solstice) // Evaluates to true// The two variables defined next refer to two distinct objects, both// of which represent exactly the same date.var xmas = new Date(2007, 11, 25);var solstice_plus_4 = new Date(2007, 11, 25);// But, by the rules of "compare by reference," distinct objects are not equal!(xmas != solstice_plus_4) // Evaluates to true</pre><div class="lefttitle" style="padding:0px; text-align: right"><a href="index.html" tppabs="http://www.davidflanagan.com/javascript5/index.html">Table of Examples</a></div><p><script type="text/javascript">amazon_ad_tag="davidflanagancom"; amazon_ad_width="300"; amazon_ad_height="250"; amazon_ad_logo="hide";</script><script type="text/javascript" src="../../www.assoc-amazon.com/s/ads.js" tppabs="http://www.assoc-amazon.com/s/ads.js"></script></div></body></html>?? 快捷鍵說明
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