首頁猿問求指點(diǎn)指點(diǎn)，新手

求指點(diǎn)指點(diǎn)，新手

JavaScript

AUSKEVIN1989 2015-09-14 10:48:15

我在JavaScript入門經(jīng)典（第五版），第13章根據(jù)title選擇樣式表的例子如下：<!DOCTYPE html><html><head><title>Switch stylesheets with JavaScript</title><style title="sheet1">body{background-color:white;color:red;}</style><style title="sheet2">body{background-color:black;color:yellow;}</style><style title="sheet3">body{background-color:pink;color:green;}</style><script>function ssEnable(mySheet){var change=false;var oldSheet=0;for(var i=0;i<document.styleSheets.length;i++){if(document.styleSheets[i].disabled==false){oldSheet=i;}document.styleSheets[i].disabled=true;if(document.styleSheets[i].title==mySheet){document.styleSheets[i].disabled=false;change=true;}}if(!change)document.styleSheets[oldSheet].disabled=false;return change;}function sheet(){var sheetName = prompt("Stylesheet Name?");if(!ssEnable(sheetName)){alert("Not found - original stylesheet retained.");}}window.onload=function(){document.getElementById('btn1').onclick=sheet;}</script></head><body>Switch my Stylesheet with the button below!<br/><input type="button" id="btn1" value="Change Sheet"/></body></html>我發(fā)現(xiàn)了if(!change)document.styleSheets[oldSheet].disabled=false;return change;如果將代碼加上{}中，是會彈出提示框alert("Not found - original stylesheet retained.");但是按照書中寫是沒有，為什么呢？求各位指點(diǎn)指點(diǎn)，謝謝如果把if(!change)document.styleSheets[oldSheet].disabled=false;return change;寫成：if(!change){document.styleSheets[oldSheet].disabled=false;return change;}就會彈框，而樣式也改變了

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