Javascript：變數與數組，javascript數組
Javascript變數屬於弱類型，即聲明一個變數的時候無需指定類型，並且之後可以將任何類型的數值複製給它。
代碼整理自w3school：http://www.w3school.com.cn
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範例程式碼：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><meta http-equiv="Content-Language" content="zh-cn" /><title>Javascript 變數</title><head> <style> body {background-color:#e5e5e5} span.red {color:red} </style></head><body> <h3>（一）js語句會按照它在html中的位置進行執行。</h3> <p>This is a paragraph <span class="red">before</span> script.</p> <script> document.write("Javascript!"); </script> <p>This is a paragraph <span class="red">after</span> script.</p> <h3>（二）js是弱類型</h3> <script> var x; document.write("x="+x); document.write("<br/>") x=2; document.write("x="+x); document.write("<br/>") x="hello" document.write("x="+x); document.write("<br/>") </script> <h3>（三）js定義數組</h3> <script> var arr = new Array(); arr[0]=1; arr[1]=2; arr[2]=3; document.write("arr[0]="+arr[0]+" arr[1]="+arr[1]+" arr[2]="+arr[2]+" arr[4]="+arr[4]); //其他建立數組的方式： document.write("<br/>"); var arr2 = new Array("Tom","Smith","John"); var arr3 = ["Tom","Smith","John"]; document.write("arr2[0]="+arr2[0]); document.write("<br/>"); document.write("arr3[0]="+arr3[0]); </script> <p>JS中資料不存在“下標越界”的問題。（超過數組大小取值會得到undefine） <h3>（四）js對象</h3> <script> //建立對象 var person = {"firstName":"Will","lastName":"Smith"} //取得對象的屬性值有兩種方式： var name1 = person.firstName var name2 = person["firstName"] document.write("name1:"+name1+",name2:"+name2) </script> <h3>（五）Undefined 和 Null</h3> <script> var var1; var var2 = null; var var3 = "hello" document.write("var1="+var1+", var2="+var2+", var3="+var3); document.write("<br/>"); var3 = null; document.write("var3="+var3+"<br/>"); </script> <h3>（六）聲明變數類型</h3> <script> var x = new String; var y = new Number; var z = new Array; x="hello" y=6 z=["Tom","John","Smith"] //輸出變數的類型 document.write("x:"+typeof x+"<br/>"); document.write("y:"+typeof y+"<br/>"); document.write("z:"+typeof z+"<br/>"); x = 2; document.write("set x=2, x:"+typeof x+"<br/>"); </script></body></html>
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