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標籤：text 代碼 get tracking data 對象 content 存在 一個
<!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="Content-Type" content="text/html; charset=gb2312" /><title>無標題文檔</title></head><body><script language="javascript">/** 一般性的true,false*/var flag = true;if(flag){alert('truetrue.............');}else{alert('falsefalse...........');}</script><script language="javascript">/**一個對象不存在，為null時的true,false*/var obj = document.getElementById('id');if(obj){ //儘管這裡的obj為null。可是能夠解讀為falsealert('obj不為null表示true');} else{alert('obj為null時可識別為false');}</script><script language="javascript">/** 一個對象不存在為undefined時的true,false*/var a;if(a){//儘管a的值為undefined,可是這裡能夠解讀為falsealert('a的值不為undefined解讀為true');} else {alert('a的值為undefined解讀為false');}</script></body></html>
JavaScript中BOOLEAN類型之三種情景代碼舉例
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