javascript || and &&
2015-03-08 20:31
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<!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=utf-8" /> <title>javascript || and &&</title> <script src="../../scripts/jquery.js" type="text/javascript"></script> <script src="lib/jquery.validate.js" type="text/javascript"></script> <script type="text/javascript"> $(document).ready(function() { //jQuery实现log jQuery.extend({ log:function(){console.log(arguments[0])} }); $.log("A test to understand javascript's \"||\" and \"&&\""); //先总结归纳一下: //1、只要“||”前面为false,无论“||”后面是true还是false,结果都返回“||”后面的值。 //2、只要“||”前面为true,无论“||”后面是true还是false,结果都返回“||”前面的值。 //3、只要“&&”前面是false,无论“&&”后面是true还是false,结果都将返“&&”前面的值; //4、只要“&&”前面是true,无论“&&”后面是true还是false,结果都将返“&&”后面的值; //5、&&优先级高于|| // 一、先来说说||,从字面上来说,只有前后都是false的时候才返回false,否则返回true。 $.log(true||false);// true $.log(false||true);// true $.log(true||true);// true $.log(false||false);// false $.log(0||1); // 1 $.log(2||1); // 2 $.log('a'||1);// a $.log(''||1); // 1 $.log('a'||0);// a $.log('a'||'b');// a $.log(''||0); // 0 $.log(0||''); // '' $.log(1||'a'&&2);// 1 function write(msg){ for(var i = 0; i < arguments.length; i ++){ document.write(arguments[i] + '<br />'); } } //关于 '&&' test1 = 1 && 2 && 3 && 4;//4 test2 = '0' && 2 && 3 && 4; //4 test3 = 1 && 2 && 0 && 4;//0 test4 = 2 && 'i' && 'love' && 3 && 'you';//you test5 = 'i' && 'hate' && 1 && 0 && 'you';//0 test6 = 1 && false && 'ihateyou' && '2';//false test7 = 2 && true && 'ihatehateyou' && '23';//23 test8 = 4 && true && 'undefined' && 'true' && '1';//1 test9 = 4 && true && undefined && 'true' && '1';//undefined test10 = 4 && true && 'null' && 'true' && '1';//1 test11 = 4 && true && null && 'true' && '1';//null write(test1, test2, test3, test4, test5, test6, test7, test8, test9, test10, test11); write('----------------------------------------------'); 59 //关于 '||' 60 _test1 = 1 || 2 || 3 || 4;//1 _test2 = 0 || 2 || 3 || 4;//2 _test3 = 0 || '0' || 8 || 4;//0 _test4 = 2 || 'i' || 'love' || 0 || 'you';//2 _test5 = 0 || 'hate' || 1 || 0 || 'you';//hate _test6 = false || 0 || 'ihateyou' || '2';//ihateyou _test7 = false || true || 'ihatehateyou' || '23';//true _test8 = 0 || 0 || 'undefined' || 'true' || '1';//undefined _test9 = 0 || 0|| undefined || 'true' || '1';//true _test10 = 0 || false || 'null' || 'true' || '1';//null _test11 = 0 || 0 || null || 'true' || '1';//true write(_test1, _test2, _test3, _test4, _test5, _test6, _test7, _test8, _test9, _test10, _test11); document.close(); }); </script> </head> <body> </body> </html>
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