{"id":726,"date":"2019-09-02T14:43:16","date_gmt":"2019-09-02T06:43:16","guid":{"rendered":"http:\/\/zouyang1230.com\/blog\/?p=726"},"modified":"2020-10-28T22:46:47","modified_gmt":"2020-10-28T14:46:47","slug":"js%e6%8a%80%e5%b7%a7%ef%bc%9a%e5%b7%a7%e7%94%a8%e8%bf%90%e7%ae%97%e7%ac%a6%e8%bf%9b%e8%a1%8c%e5%8f%98%e9%87%8f%e8%b5%8b%e5%80%bc%e4%b8%8e%e6%9d%a1%e4%bb%b6%e5%88%a4%e6%96%ad","status":"publish","type":"post","link":"http:\/\/www.imzouyang.com\/blog\/archives\/726.html","title":{"rendered":"js\u6280\u5de7\uff1a\u5de7\u7528\u8fd0\u7b97\u7b26&&"},"content":{"rendered":"

\u4e00\u3001&&\u8fd0\u7b97\u7b26\u5728\u53d8\u91cf\u8d4b\u503c\u65f6\u7684\u8fd0\u7528\uff08\u77ed\u8def\u539f\u7406\uff09\uff1a<\/h4>\n

1\u3001\u5148\u770b\u4e00\u4e2a\u793a\u4f8b\uff1a<\/h5>\n
\nvar box = true && 123;\nconsole.log(box);\t\/\/123\n\nvar box = false && 123;\nconsole.log(box);\t\/\/false\n\nvar box = 0 && 123;\nconsole.log(box);\t\/\/0\n\nvar box = -1 && 123;\nconsole.log(box);\t\/\/123\n\n<\/code><\/pre>\n
\u4ece\u4e0a\u4f8b\u53ef\u4ee5\u770b\u51fa\uff0c&&\u8fd0\u7b97\u7b26\u5de6\u4fa7\u5982\u679c\u4e3a\u771f\uff0c\u5219\u8d4b\u503c\u53f3\u4fa7\u503c\uff08\u53cd\u4e4b\uff0c\u5219\u8d4b\u503c\u5de6\u4fa7\u503c\uff09\u3002<\/p>\n
<\/p>\n
2\u3001\u77e5\u8bc6\u70b9\uff1a<\/h5>\n
&&\u8fd0\u7b97\u7b26\u5de6\u4fa7\u90e8\u5206\u8f6c\u5e03\u5c14\u503c\u540e\u4e3atrue\uff0c\u5219\u8d4b\u503c&&\u8fd0\u7b97\u7b26\u53f3\u4fa7\u7684\uff08\u5426\u5219\u8d4b\u503c\u5de6\u4fa7\uff09\uff0c\u76f8\u5f53\u4e8e\u5de6\u4fa7\u662f\u4e2a\u6761\u4ef6\u5224\u65ad\uff0c\u4e3a\u771f\u5219\u7ee7\u7eed\u8d4b\u503c\u53f3\u4fa7\u3002
\u5f53\u5de6\u4fa7\u4e3a null\/NaN\/undefined\uff0c\u4f1a\u8d4b\u503c\u4e3a null\/NaN\/undefined :<\/p>\n
\nconsole.log( null && 123 );\t\/\/null\n\nconsole.log( NaN && 123 );\t\/\/NaN\n\nconsole.log( undefined && 123 );\t\/\/undefined\n\n<\/code><\/pre>\n
3\u3001\u8fdb\u9636\uff1a<\/h5>\n
\u5229\u7528&&\u8fd0\u7b97\u7b26\u6211\u4eec\u53ef\u4ee5\u5199\u51fa\u66f4\u52a0\u7b80\u6d01\u7684\u4ee3\u7801\uff1a<\/p>\n
\n\/\/\u793a\u4f8b1\uff1aif\u6761\u4ef6\u6267\u884c\u7684\u7b80\u5316\n\/\/ if(true) DoSomething...  \u7b80\u5316\u4e3a  true && DoSomething... \nvar box1 = true, box2 = true,box3 = true,box4 = false,box5 = true;\nbox1 && console.log(\"1\");  \/\/1\nbox2 && console.log(\"2\");  \/\/2\nbox3 && console.log(\"3\");  \/\/3\nbox4 && console.log(\"4\");  \/\/\u4e0d\u6253\u5370\u4efb\u4f55\u4e1c\u897f\nbox5 && console.log(\"5\");  \/\/5\n\n\/\/\u793a\u4f8b2\uff1a\u5224\u65ad\u540e\u7684\u8d4b\u503c\u64cd\u4f5c\nvar box1;\nvar box2 = 1;\nif( box2 )\n{\n\tbox1 = box2;\n}\nconsole.log( box1 );  \/\/1\n\n\/\/\u6539\u5199\u4e3a\uff1a\nvar box1 = window.box2 && 1;\nconsole.log( box1 );  \/\/1\n\n\n\n\/\/\u793a\u4f8b3\uff1a\u591a\u4e2a&&\u7684\u60c5\u51b5\nvar box1 = 1 && 2 && 3 && 4;  \/\/\u524d\u9762\u90fd\u4e3a\u771f\uff0c\u6700\u540e\u8d4b\u503c\u7ed94\nconsole.log( box1 );\t\/\/4\n\nvar box2 = 1 && 2 && 0 && 4;  \/\/\u524d\u9762\u52300\u65f6\uff0c\u5c31\u52690 && 4\uff0c\u6240\u4ee5\u6700\u540e\u8d4b\u503c\u7ed90\nconsole.log( box2  ); \t\/\/0\n<\/code><\/pre>\n
\n\/\/\u793a\u4f8b4\uff1a\u5728 React \u7ec4\u4ef6\u5185\u6761\u4ef6\u5224\u65ad\u663e\u793a\u9700\u8981\u7684\u7ec4\u4ef6\nfunction<\/span> Mailbox<\/span>(<\/span>props<\/span>)<\/span> {<\/span>\n  const<\/span> unreadMessages =<\/span> props.<\/span>unreadMessages;<\/span>\n  return<\/span> (<\/span>\n    <<\/span>div><\/span><\/span>\n      <<\/span>h1><\/span><\/span>Hello!<\/span><\/<\/span>h1><\/span><\/span>\n      {<\/span>unreadMessages.<\/span>length ><\/span> 0<\/span> &&
<\/span><\/span>        <<\/span>h2>
<\/span><\/span><\/span>          You have <\/span>{<\/span>unreadMessages.<\/span>length}<\/span> unread messages.
<\/span><\/span>        <\/<\/span>h2>
<\/span><\/span><\/span>      }
<\/span><\/span>    <\/<\/span>div><\/span><\/span>\n  )<\/span>;<\/span>\n}<\/span><\/code>\n<\/pre>\n
\u4e8c\u3001&&\u8fd0\u7b97\u7b26\u5728\u6761\u4ef6\u5224\u65ad\u65f6\u7684\u8fd0\u7528\uff1a<\/h4>\n
1\u3001\u5148\u770b\u4e00\u4e2a\u793a\u4f8b\uff1a<\/h5>\n
\nvar x = 1, y = 2, z = 3;\nif( x==1 && y==2 )\n{\n  console.log(true);  \/\/\u6253\u5370\u51fatrue \uff0c\u56e0\u4e3ax==1 \u548c y==2 \u8fd9\u4e24\u4e2a\u6761\u4ef6\u90fd\u4e3a\u771f\uff0c\u5219\u6574\u4f53\u8fd4\u56de\u771f\n}\nconsole.log( x==1 && y==3 );  \/\/false\nconsole.log( x==1 && y==2 && z == 4 );  \/\/false\n\n<\/code><\/pre>\n
2\u3001\u77e5\u8bc6\u70b9\uff1a<\/h5>\n
&&\u8fd0\u7b97\u7b26\u7528\u4e8e\u6761\u4ef6\u5224\u65ad\u65f6\uff0c\u5fc5\u987b\u5de6\u53f3\u4e24\u4fa7\u5168\u90e8\u4e3a\u771f\u624d\u8fd4\u56de\u771f\uff0c\u5426\u5219\u5047\uff08\u53ea\u8981\u5176\u4e2d\u6709\u4e00\u4e2a\uff09<\/p>\n
<\/p>\n\n\n
\u4e09\u3001\u5b9e\u73b0\u8fde\u7eed\u7684\u6761\u4ef6\u51fd\u6570\u6267\u884c\uff0c\u6bd4\u5982\uff1a\u5206\u522b\u6267\u884c\u4e09\u4e2a\u51fd\u6570<\/p>\n\n\n\n
\u793a\u4f8b1\uff1a\nfunction box1(){\n    console.log( \"01\" );\n    return true;     \/\/\u8fd4\u56de \u771f\uff0c\u624d\u4f1a\u8ba9\u7b2c\u4e8c\u4e2a\u51fd\u6570\u5f97\u4ee5\u7ee7\u7eed\u6267\u884c\n}\nfunction box2(){\n    console.log( \"02\" );\n    return true;     \/\/\u8fd4\u56de \u771f\uff0c\u624d\u4f1a\u8ba9\u7b2c\u4e09\u4e2a\u51fd\u6570\u5f97\u4ee5\u7ee7\u7eed\u6267\u884c\n}\nfunction box3(){\n    console.log( \"03\" );\n}\nbox1()&&box2()&&box3()  \/\/01  02  03\n\n\u793a\u4f8b2\uff1a\n\u5982\u679c\u7b2c\u4e00\u4e2a\u51fd\u6570\u8fd4\u56de \u5047\uff0c\u5219\u4e0d\u6267\u884c\u540e\u9762\u51fd\u6570\uff1a\nfunction box1(){\n    console.log( \"01\" );\n    return false\n}\nfunction box2(){\n    console.log( \"02\" );\n    return true\n}\nfunction box3(){\n    console.log( \"03\" );\n}\nbox1()&&box2()&&box3()  \/\/01<\/code><\/pre>\n\n\n\n

\uff08\u5b8c\uff09<\/p>\n","protected":false},"excerpt":{"rendered":"
\u4e00\u3001&&\u8fd0\u7b97\u7b26\u5728\u53d8\u91cf\u8d4b\u503c\u65f6\u7684\u8fd0\u7528\uff08\u77ed\u8def\u539f\u7406\uff09\uff1a 1\u3001\u5148\u770b\u4e00\u4e2a\u793a\u4f8b\uff1a var box = tru … \u7ee7\u7eed\u9605\u8bfb js\u6280\u5de7\uff1a\u5de7\u7528\u8fd0\u7b97\u7b26&&<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"aside","meta":[],"categories":[30],"tags":[],"_links":{"self":[{"href":"http:\/\/www.imzouyang.com\/blog\/wp-json\/wp\/v2\/posts\/726"}],"collection":[{"href":"http:\/\/www.imzouyang.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.imzouyang.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.imzouyang.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.imzouyang.com\/blog\/wp-json\/wp\/v2\/comments?post=726"}],"version-history":[{"count":14,"href":"http:\/\/www.imzouyang.com\/blog\/wp-json\/wp\/v2\/posts\/726\/revisions"}],"predecessor-version":[{"id":2297,"href":"http:\/\/www.imzouyang.com\/blog\/wp-json\/wp\/v2\/posts\/726\/revisions\/2297"}],"wp:attachment":[{"href":"http:\/\/www.imzouyang.com\/blog\/wp-json\/wp\/v2\/media?parent=726"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.imzouyang.com\/blog\/wp-json\/wp\/v2\/categories?post=726"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.imzouyang.com\/blog\/wp-json\/wp\/v2\/tags?post=726"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}