{"id":105949,"date":"2026-09-16T12:56:27","date_gmt":"2026-09-16T04:56:27","guid":{"rendered":"https:\/\/www.wsisp.com\/helps\/105949.html"},"modified":"2026-09-16T12:56:27","modified_gmt":"2026-09-16T04:56:27","slug":"05-%e6%9d%a1%e4%bb%b6%e5%88%a4%e6%96%ad%ef%bc%9a-%e6%89%8d%e6%98%af%e6%ad%a3%e9%81%93%ef%bc%88if-else-%c2%b7-%e9%80%bb%e8%be%91%e8%bf%9e%e6%8e%a5%e8%af%8d-%c2%b7-%e4%b8%89%e5%85%83-%c2%b7-switch","status":"publish","type":"post","link":"https:\/\/www.wsisp.com\/helps\/105949.html","title":{"rendered":"05 \u6761\u4ef6\u5224\u65ad\uff1a=== \u624d\u662f\u6b63\u9053\uff08if\/else \u00b7 \u903b\u8f91\u8fde\u63a5\u8bcd \u00b7 \u4e09\u5143 \u00b7 switch\uff09"},"content":{"rendered":"

\u4e0a\u4e00\u7bc7：04 \u6570\u5b57\u4e0e\u5b57\u7b26\u4e32：+ \u53f7\u7684\u4e24\u526f\u9762\u5b54（\u62fc\u63a5\u4e0e\u76f8\u52a0 \u00b7 NaN \u00b7 \u7c7b\u578b\u4e92\u8f6c \u00b7 \u6a21\u677f\u5b57\u7b26\u4e32）<\/p>\n

\n

\u4e0a\u7bc7\u7ec3\u4e60\u53c2\u8003\u7b54\u6848<\/h3>\n

\u7ec3\u4e60 1（\u624b\u52a8\u6a21\u62df）：\u624b\u52a8\u6a21\u62df（\u5148\u5199\u7b54\u6848\u518d\u56de\u8f66）：\u201c10\u201d + 5\u300110 + 5 + \u201c5\u201d\u3001\u201c10\u201d – 5\u3001\u201c3\u201d * \u201c4\u201d \u5404\u5f97\u4ec0\u4e48？ \"\u5728\u8fd9\u91cc\u63d2\u5165\u56fe\u7247\u63cf\u8ff0\"<\/p>\n

\u89c4\u5f8b\u6536\u53e3：\u53ea\u6709 + \u9047\u6587\u5219\u6587，\u5176\u4ed6\u8fd0\u7b97\u7b26\u9047\u6587\u8f6c\u6570\u3002<\/p>\n

\u7ec3\u4e60 2（\u9884\u6d4b\u518d\u9a8c\u8bc1）：\u9884\u6d4b\u518d\u9a8c\u8bc1：Number(\u201c\u201d)\u3001Number(\u201c12 8\u201d)\u3001parseInt(\u201c12 8\u201d)\u3001parseFloat(\u201c3.5\u6298\u201d) \u7684\u7ed3\u679c\u5404\u662f\u4ec0\u4e48？\u54ea\u4e2a\u51fa\u4e4e\u4f60\u610f\u6599？ \"\u5728\u8fd9\u91cc\u63d2\u5165\u56fe\u7247\u63cf\u8ff0\" Number("") \u5f97 0（\u5386\u53f2\u51b3\u5b9a）； Number("12 8") \u5f97 NaN\u2014\u2014\u4e2d\u95f4\u7684\u7a7a\u683c\u7b97\u6742\u8d28，\u4e25\u683c\u6d3e\u76f4\u63a5\u62d2\u7edd； parseInt("12 8") \u5f97 12\u2014\u2014\u8585\u5230\u7a7a\u683c\u5c31\u505c； parseFloat("3.5\u6298") \u5f97 3.5； \u51fa\u4e4e\u610f\u6599\u7684\u591a\u534a\u662f\u524d\u4e24\u4e2a：\u7a7a\u4e32\u53d8 0\u3001\u4e00\u4e2a\u7a7a\u683c\u5c31\u80fd\u6bd2\u6b7b Number\u3002<\/p>\n

\u7ec3\u4e60 3（\u6539\u9020\u8981\u70b9）：\u6539\u9020\u8981\u70b9：\u8d26\u5355\u52a0\u7b2c\u56db\u7b14\u9910\u8d39 \u201c128\u5143\u201d（\u70e7\u70e4）\u2014\u2014\u6570\u636e\u533a\u52a0\u4e00\u884c\u3001\u5408\u8ba1\u5904\u52a0\u4e00\u9879，\u91cd\u8dd1；\u987a\u4fbf\u89c2\u5bdf"\u4e8b\u6545\u8fd8\u539f"\u90a3\u884c\u8ddf\u7740\u53d8\u957f\u4e86\u591a\u5c11； \u6570\u636e\u533a\u52a0 const bill4 = "128\u5143"; \u6d17\u51fa food4 = parseFloat(bill4) \u5408\u8ba1\u52a0\u4e00\u9879\u2014\u2014"\u4e8b\u6545\u8fd8\u539f"\u90a3\u884c\u53d8\u6210 "198\u5143225\u5143217\u5143128\u5143"，\u53c8\u957f\u4e00\u622a \u6bcf\u52a0\u4e00\u7b14\u4e0d\u6d17\u7684\u8d26，\u9b3c\u8bdd\u5c31\u957f\u4e00\u622a\u3002<\/p>\n

\u7ec3\u4e60 4（\u75ab\u82d7\u63ed\u6653）：\u4eba\u5747 87.56 \u5143，\u9884\u7b97\u7ebf 90 \u5143\u2014\u2014\u201c\u8d85\u6ca1\u8d85"\u662f\u4e2a\u662f\u975e\u9898，\u7a0b\u5e8f\u9760\u4ec0\u4e48\u56de\u7b54\u662f\u975e\u9898？\u63a7\u5236\u53f0\u8bd5\u8bd5 console.log(87.56 > 90)；\u518d\u8bd5\u8bd5 console.log(\u201c10\u201d < \u201c9\u201d)\u2014\u2014\u7ed3\u679c\u7adf\u7136\u662f true，10 \u4e3a\u4ec0\u4e48\u4f1a\u5c0f\u4e8e 9？05 \u7bc7\u63ed\u6653\u6bd4\u8f83\u8fd0\u7b97\u7b26\u7684\u5751，\u548c JS \u4e16\u754c\u6700\u91cd\u8981\u7684\u4e09\u6761\u7b49\u53f7\u3002 87.56 > 90 \u5f97 false，\u6ca1\u8d85\u9884\u7b97，"10" < "9" \u5f97 true\u2014\u2014\u6bd4\u8f83\u8fd0\u7b97\u7b26\u4e24\u8fb9\u90fd\u662f\u5b57\u7b26\u4e32\u65f6\u4e0d\u8f6c\u6570\u5b57，\u6539\u8d70\u5b57\u5178\u5e8f：\u50cf\u67e5\u5b57\u5178\u4e00\u6837\u9010\u5b57\u7b26\u6bd4，\u7b2c\u4e00\u4f4d "1" \u6392\u5728 "9" \u524d\u9762，\u4e8e\u662f "10" \u6574\u4f53"\u5c0f\u4e8e\u201d "9"\u3002\u6559\u8bad：\u6570\u5b57\u6bd4\u8f83\u524d\u5148\u6d17\u7c7b\u578b\u3002\u4eca\u5929\u5c31\u628a"\u6bd4\u8f83"\u8fde\u540c"\u5224\u65ad"\u4e00\u6b21\u8bb2\u900f，\u987a\u4fbf\u7acb JS \u4e16\u754c\u6700\u91cd\u8981\u7684\u4e00\u6761\u519b\u89c4\u3002<\/p>\n

\n

\u4e00\u3001\u573a\u666f\u5f15\u5165：\u8def\u53e3\u4e0e\u88c1\u5224<\/h3>\n

\"\u5728\u8fd9\u91cc\u63d2\u5165\u56fe\u7247\u63cf\u8ff0\"<\/p>\n

\u524d\u56db\u7bc7\u7684\u7a0b\u5e8f\u90fd\u662f\u4e00\u6761\u9053\u8d70\u5230\u9ed1\u2014\u2014\u4ece\u4e0a\u5230\u4e0b\u6bcf\u884c\u90fd\u6267\u884c\u3002\u4f46\u771f\u5b9e\u4e16\u754c\u5904\u5904\u662f\u5c94\u8def\u53e3：\u6210\u7ee9 85 \u8d70"\u826f\u597d"\u5c94\u53e3，59 \u8d70"\u8865\u8003"\u5c94\u53e3；\u5bc6\u7801\u5bf9\u8d70"\u653e\u884c"，\u9519\u8d70"\u91cd\u8bd5"\u3002\u7a0b\u5e8f\u7684"\u806a\u660e"\u4ece\u4eca\u5929\u5f00\u59cb：\u8ba9\u4ee3\u7801\u81ea\u5df1\u9009\u8def\u3002<\/p>\n

\u672c\u7bc7\u8fd8\u8981\u7acb\u4e00\u6761 JS \u7279\u6709\u7684\u519b\u89c4：\u5224\u65ad\u76f8\u7b49\u6c38\u8fdc\u7528\u4e09\u4e2a\u7b49\u53f7 ===\u3002\u7528\u4e24\u4e2a\u7b49\u53f7，\u4f60\u4f1a\u6536\u83b7 "1" == 1 \u4e3a true\u3001"" == 0 \u4e3a true \u8fd9\u4e9b\u60ca\u609a\u7ed3\u679c\u2014\u2014\u5b83\u4eec\u662f JS \u9762\u8bd5\u7684\u7ecf\u5178\u9001\u547d\u9898，\u66f4\u662f\u771f\u5b9e\u9879\u76ee\u91cc\u903b\u8f91\u9b3c\u755c\u7684\u5934\u53f7\u6765\u6e90\u3002<\/p>\n

\u4e8c\u3001\u672c\u7bc7\u76ee\u6807<\/h3>\n
  • \u4f1a\u5199 if \/ else if \/ else \u591a\u7ea7\u5206\u652f；<\/li>\n
  • \u7acb === \u519b\u89c4，\u8ba4\u6e05 == \u7684\u9690\u5f0f\u8f6c\u6362\u5751；<\/li>\n
  • \u638c\u63e1 &&\u3001||\u3001! \u4e09\u4e2a\u903b\u8f91\u8fde\u63a5\u8bcd；<\/li>\n
  • \u4f1a\u7528\u4e09\u5143\u8868\u8fbe\u5f0f\u5728\u6a21\u677f\u5b57\u7b26\u4e32\u91cc"\u5c31\u5730\u5206\u5c94"；<\/li>\n
  • \u8ba4\u8bc6 switch：\u540c\u4e00\u4e2a\u53d8\u91cf\u591a\u503c\u5339\u914d\u65f6\u7684\u6e05\u723d\u5199\u6cd5\u3002<\/li>\n

    \u4e09\u3001\u77e5\u8bc6\u70b9\u8bb2\u89e3<\/h3>\n

    3.1 if \/ else：\u5e03\u5c14\u5f53\u88c1\u5224<\/h4>\n

    const<\/span> score =<\/span> 85<\/span>;<\/span>
    \nif<\/span> (<\/span>score >=<\/span> 90<\/span>)<\/span> {<\/span>
    \n console.<\/span>log<\/span>(<\/span>"\u4f18\u79c0"<\/span>)<\/span>;<\/span>
    \n}<\/span> else<\/span> if<\/span> (<\/span>score >=<\/span> 60<\/span>)<\/span> {<\/span>
    \n console.<\/span>log<\/span>(<\/span>"\u53ca\u683c"<\/span>)<\/span>;<\/span>
    \n}<\/span> else<\/span> {<\/span>
    \n console.<\/span>log<\/span>(<\/span>"\u4e0d\u53ca\u683c"<\/span>)<\/span>;<\/span>
    \n}<\/span><\/p>\n

    \"\u5728\u8fd9\u91cc\u63d2\u5165\u56fe\u7247\u63cf\u8ff0\"<\/p>\n

    \u8bed\u6cd5\u8981\u70b9：\u6761\u4ef6\u5199\u5728\u5c0f\u62ec\u53f7\u91cc，\u5927\u62ec\u53f7\u5305\u4f4f"\u6761\u4ef6\u6210\u7acb\u624d\u6267\u884c\u7684\u4ee3\u7801"；else if \u53ef\u4ee5\u8fde\u5f88\u591a\u7ea7；\u4ece\u4e0a\u5f80\u4e0b\u4f9d\u6b21\u68c0\u67e5，\u547d\u4e2d\u4e00\u4e2a\u5c94\u53e3\u5c31\u8fdb，\u540e\u9762\u5168\u90e8\u8df3\u8fc7\u2014\u201485 \u547d\u4e2d >= 60，\u4e0d\u518d\u770b else\u3002<\/p>\n

    \u6bd4\u8f83\u8fd0\u7b97\u7b26\u5168\u5bb6\u798f：> >= < <= ===（\u76f8\u7b49）!==（\u4e0d\u7b49）\u3002\u5b83\u4eec\u7684\u4ea7\u51fa\u6c38\u8fdc\u662f\u5e03\u5c14\u503c\u2014\u201403 \u7bc7\u8bf4\u5e03\u5c14\u662f\u5224\u65ad\u71c3\u6599，\u73b0\u5728\u6b63\u5f0f\u70b9\u706b\u3002<\/p>\n

    falsy \u516d\u5144\u5f1f：\u5c0f\u62ec\u53f7\u91cc\u7684\u6761\u4ef6\u5176\u5b9e\u4e0d\u4e00\u5b9a\u662f\u5e03\u5c14，JS \u4f1a\u81ea\u52a8\u8f6c\u6362\u3002\u53ea\u6709\u516d\u4e2a\u503c\u4f1a\u88ab\u8f6c\u6210 false：false\u30010\u3001""\u3001null\u3001undefined\u3001NaN，\u5176\u4f59\u4e00\u5207\u8f6c\u6210 true（\u8fde "false" \u8fd9\u4e2a\u5b57\u7b26\u4e32\u90fd\u662f true！）\u3002\u5efa\u8bae：\u6761\u4ef6\u91cc\u6c38\u8fdc\u5199\u660e\u786e\u7684\u6bd4\u8f83（\u5982 score >= 60），\u628a\u9690\u5f0f\u8f6c\u6362\u7559\u7ed9\u8bfb\u65e7\u4ee3\u7801\u7684\u65f6\u5019\u3002<\/p>\n

    3.2 === \u519b\u89c4：\u4e09\u4e2a\u7b49\u53f7\u624d\u662f\u6b63\u9053<\/h4>\n

    === \u5168\u7b49：\u503c\u548c\u7c7b\u578b\u90fd\u76f8\u540c\u624d\u7b97\u76f8\u7b49\u3002== \u5bbd\u677e：\u5148\u505a\u4e00\u8f6e\u9690\u5f0f\u8f6c\u6362\u518d\u6bd4\u2014\u2014\u8f6c\u6362\u89c4\u5219\u590d\u6742\u5230\u80fd\u51fa\u9762\u8bd5\u9898：<\/p>\n\n\u8868\u8fbe\u5f0f\u7ed3\u679c\u4eba\u8bdd\u7ffb\u8bd1<\/tr>\n\n\n\n\n\n\n
    "1" == 1<\/td>\ntrue<\/td>\n\u5b57\u7b26\u4e32\u88ab\u8f6c\u6210\u6570\u5b57\u518d\u6bd4<\/td>\n<\/tr>\n
    "" == 0<\/td>\ntrue<\/td>\n\u7a7a\u4e32\u88ab\u8f6c\u6210 0<\/td>\n<\/tr>\n
    0 == false<\/td>\ntrue<\/td>\n\u6570\u5b57\u88ab\u8f6c\u6210\u5e03\u5c14<\/td>\n<\/tr>\n
    null == undefined<\/td>\ntrue<\/td>\n\u4e24\u4e2a"\u7a7a"\u88ab\u7279\u5224\u76f8\u7b49<\/td>\n<\/tr>\n
    "1" === 1<\/td>\nfalse<\/td>\n\u7c7b\u578b\u4e0d\u540c，\u76f4\u63a5\u4e0d\u7b49，\u5e72\u51c0\u5229\u843d<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

    \u519b\u89c4\u53ea\u6709\u4e00\u53e5：\u81ea\u5df1\u5199\u4ee3\u7801，\u6bd4\u8f83\u76f8\u7b49\u53ea\u7528 ===；== \u7559\u7ed9\u8bfb\u522b\u4eba\u7684\u8001\u4ee3\u7801\u65f6"\u8ba4\u8bc6\u5b83"\u3002\u5b83\u548c 04 \u7bc7\u7684\u9690\u5f0f\u8f6c\u6362\u662f\u540c\u4e00\u6b3e\u8d4c\u2014\u2014\u5bbd\u677e\u7b49\u53f7\u8d4c\u7684\u662f"\u8f6c\u6362\u89c4\u5219\u6070\u597d\u5982\u4f60\u6240\u613f"，\u800c\u89c4\u5219\u8868\u957f\u5f97\u6ca1\u4eba\u80cc\u5f97\u5b8c\u3002\u540c\u7406，\u4e0d\u7b49\u7528 !==，\u522b\u7528 !=\u3002<\/p>\n

    3.3 \u903b\u8f91\u8fde\u63a5\u8bcd：&&\u3001||\u3001!<\/h4>\n

    \u771f\u5b9e\u6761\u4ef6\u5e38\u5e38\u662f\u590d\u5408\u7684\u2014\u2014"90 \u5206\u5e76\u4e14\u5168\u52e4"\u624d\u6709\u5956\u5b66\u91d1：<\/p>\n

    const<\/span> hasScholarship =<\/span> score >=<\/span> 90<\/span> &&<\/span> attendance ===<\/span> "\u5168\u52e4"<\/span>;<\/span> \/\/ \u5e76\u4e14：\u4e24\u8fb9\u90fd\u771f\u624d\u771f<\/span>
    \nconst<\/span> canMakeup =<\/span> score <<\/span> 60<\/span> ||<\/span> score ===<\/span> –<\/span>1<\/span>;<\/span> \/\/ \u6216\u8005：\u4e00\u8fb9\u771f\u5c31\u771f<\/span>
    \nconst<\/span> isAbsent =<\/span> !<\/span>(<\/span>score >=<\/span> 0<\/span>)<\/span>;<\/span> \/\/ \u53d6\u53cd：\u771f\u5047\u4e92\u6362<\/span><\/p>\n

    \u53e3\u8bc0：&& \u6536\u7d27（\u90fd\u5f97\u6ee1\u8db3），|| \u653e\u5bbd（\u6ee1\u8db3\u5176\u4e00），! \u53cd\u7740\u8bf4\u3002\u590d\u5408\u6761\u4ef6\u5efa\u8bae\u5148\u5b58\u8fdb\u4e00\u4e2a\u89c1\u540d\u77e5\u610f\u7684\u5e03\u5c14\u53d8\u91cf（\u5982 hasScholarship），if \u91cc\u53ea\u5199\u53d8\u91cf\u540d\u2014\u2014\u6bd4\u628a\u4e09\u884c\u903b\u8f91\u585e\u8fdb\u5c0f\u62ec\u53f7\u53ef\u8bfb\u5341\u500d\u3002<\/p>\n

    \u77ed\u8def\u6c42\u503c（\u9644\u8d60\u51b7\u77e5\u8bc6）：&& \u548c || \u6267\u884c\u65f6\u8fd8\u4f1a"\u5077\u61d2"\u2014\u2014A && B \u82e5 A \u662f falsy，\u53f3\u8fb9\u770b\u90fd\u4e0d\u770b，\u76f4\u63a5\u8fd4\u56de A；A || B \u82e5 A \u662f truthy，\u540c\u6837\u76f4\u63a5\u8fd4\u56de A\u3002\u8fd9\u4e2a\u7279\u6027\u6700\u51fa\u540d\u7684\u7528\u6cd5\u662f\u515c\u5e95\u9ed8\u8ba4\u503c：<\/p>\n

    const<\/span> input =<\/span> ""<\/span>;<\/span> \/\/ \u7528\u6237\u6ca1\u586b，\u7a7a\u4e32\u662f falsy<\/span>
    \nconst<\/span> name =<\/span> input ||<\/span> "\u533f\u540d\u7528\u6237"<\/span>;<\/span> \/\/ \u5de6\u8fb9\u6ca1\u8d27，\u53d6\u53f3\u8fb9\u7684\u515c\u5e95<\/span>
    \nconsole.<\/span>log<\/span>(<\/span>name)<\/span>;<\/span> \/\/ \u533f\u540d\u7528\u6237<\/span><\/p>\n

    \"\u5728\u8fd9\u91cc\u63d2\u5165\u56fe\u7247\u63cf\u8ff0\"<\/p>\n

    \u903b\u8f91：input \u6709\u771f\u5185\u5bb9\u5c31\u7528\u5b83，\u662f\u7a7a\u4e32\/null\/undefined \u8fd9\u7c7b"\u6ca1\u8d27"\u503c\u5c31\u6362\u9ed8\u8ba4\u503c\u300217 \u7bc7\u4ece localStorage \u53d6\u5b58\u6863\u65f6\u4f1a\u7528\u5230\u8fd9\u62db\u2014\u2014\u7b2c\u4e00\u6b21\u8bbf\u95ee\u8fd8\u6ca1\u5b58\u8fc7\u6863，\u53d6\u51fa\u6765\u662f null，\u7528 || \u4e00\u884c\u515c\u5e95，\u4f18\u96c5\u4e0d\u5d29\u3002\u73b0\u5728\u6df7\u4e2a\u8138\u719f，\u5230\u65f6\u5019\u4f1a\u5fc3\u4e00\u7b11\u3002<\/p>\n

    3.4 \u4e09\u5143\u8868\u8fbe\u5f0f：\u5c31\u5730\u5206\u5c94\u7684\u5c0f if<\/h4>\n

    \u6761\u4ef6 ? A : B<\/p>\n

    \u6761\u4ef6\u771f\u53d6 A\u3001\u5047\u53d6 B\u3002\u5b83\u662f\u8868\u8fbe\u5f0f（\u6709\u503c），\u6240\u4ee5\u80fd\u76f4\u63a5\u585e\u8fdb\u6a21\u677f\u5b57\u7b26\u4e32：<\/p>\n

    const<\/span> score =<\/span> 85<\/span>;<\/span>
    \nconsole.<\/span>log<\/span>(<\/span>`<\/span>\u7ed3\u679c：<\/span>${<\/span>score >=<\/span> 60<\/span> ?<\/span> "\u901a\u8fc7"<\/span> :<\/span> "\u8865\u8003"<\/span>}<\/span><\/span>`<\/span><\/span>)<\/span>;<\/span><\/p>\n

    \"\u5728\u8fd9\u91cc\u63d2\u5165\u56fe\u7247\u63cf\u8ff0\"<\/p>\n

    \u4e00\u53e5\u8bdd\u5b8c\u6210\u5206\u5c94，\u62a5\u8868\u548c\u770b\u677f\u91cc\u9ad8\u9891\u51fa\u573a\u3002\u6ce8\u610f\u5b83\u53ea\u9002\u5408"\u4e8c\u9009\u4e00"\u2014\u2014\u4e09\u5c94\u4ee5\u4e0a\u8001\u5b9e\u7528 if\u3002<\/p>\n

    3.5 switch：\u591a\u503c\u5339\u914d\u7684\u6e05\u723d\u5199\u6cd5<\/h4>\n

    \u540c\u4e00\u4e2a\u53d8\u91cf\u6bd4\u5bf9\u591a\u4e2a\u5177\u4f53\u503c\u65f6，if\/else \u94fe\u5199\u7740\u5570\u55e6，switch \u66f4\u6e05\u723d：<\/p>\n

    const<\/span> level =<\/span> "B"<\/span>;<\/span>
    \nswitch<\/span> (<\/span>level)<\/span> {<\/span>
    \n case<\/span> "A"<\/span>:<\/span> console.<\/span>log<\/span>(<\/span>"\u4f18\u79c0"<\/span>)<\/span>;<\/span> break<\/span>;<\/span>
    \n case<\/span> "B"<\/span>:<\/span> console.<\/span>log<\/span>(<\/span>"\u826f\u597d"<\/span>)<\/span>;<\/span> break<\/span>;<\/span>
    \n case<\/span> "C"<\/span>:<\/span> console.<\/span>log<\/span>(<\/span>"\u53ca\u683c"<\/span>)<\/span>;<\/span> break<\/span>;<\/span>
    \n default<\/span>:<\/span> console.<\/span>log<\/span>(<\/span>"\u5176\u4ed6"<\/span>)<\/span>;<\/span>
    \n}<\/span><\/p>\n

    \"\u5728\u8fd9\u91cc\u63d2\u5165\u56fe\u7247\u63cf\u8ff0\"<\/p>\n

    \u4e24\u6761\u5fc5\u5b88\u7684\u89c4\u77e9：<\/p>\n

      \n
    • \u6bcf\u4e2a case \u672b\u5c3e\u5199 break\u2014\u2014\u6f0f\u4e86 break，\u547d\u4e2d\u540e\u4f1a"\u6f0f"\u5230\u4e0b\u4e00\u4e2a case \u7ee7\u7eed\u6267\u884c，\u7ecf\u5178\u5751；<\/li>\n
    • switch \u7684\u5339\u914d\u7528\u7684\u662f ===（\u4e25\u683c\u76f8\u7b49）\u2014\u2014case "A" \u5339\u914d\u4e0d\u4e0a "a"，\u5927\u5c0f\u5199\u654f\u611f\u3002<\/li>\n<\/ul>\n

      default \u662f\u5168\u90fd\u4e0d\u4e2d\u65f6\u7684\u515c\u5e95，\u76f8\u5f53\u4e8e else\u3002\u6ce8\u610f\u5206\u5de5：\u6bd4\u5bf9\u5177\u4f53\u503c\u7528 switch，\u6bd4\u5bf9\u8303\u56f4（\u5206\u6570\u6bb5）\u7528 if\u2014\u2014switch \u5199\u4e0d\u4e86 >= 60\u3002<\/p>\n

      \u56db\u3001\u5b8c\u6574\u5b9e\u6218：\u6210\u7ee9\u5224\u5b9a\u5668<\/h3>\n

      \u628a\u4e94\u79cd\u5224\u65ad\u5de5\u5177\u62fc\u6210\u4e00\u53f0\u5b8c\u6574\u7684"\u5224\u5b9a\u673a"\u3002\u65b0\u5efa \u6210\u7ee9\u5224\u5b9a\u5668.html：<\/p>\n

      <!<\/span>DOCTYPE<\/span> html<\/span>><\/span><\/span>
      \n<<\/span>html<\/span> lang<\/span>=<\/span>"<\/span>zh-CN"<\/span><\/span>><\/span><\/span>
      \n<<\/span>head<\/span>><\/span><\/span>
      \n <<\/span>meta<\/span> charset<\/span>=<\/span>"<\/span>UTF-8"<\/span><\/span>><\/span><\/span>
      \n <<\/span>title<\/span>><\/span><\/span>\u6210\u7ee9\u5224\u5b9a\u5668<\/<\/span>title<\/span>><\/span><\/span>
      \n<\/<\/span>head<\/span>><\/span><\/span>
      \n<<\/span>body<\/span>><\/span><\/span>
      \n <<\/span>h2<\/span>><\/span><\/span>\u6210\u7ee9\u5224\u5b9a\u5668<\/<\/span>h2<\/span>><\/span><\/span>
      \n <<\/span>p<\/span>><\/span><\/span>\u5224\u5b9a\u62a5\u544a\u5728\u63a7\u5236\u53f0\u2014\u2014\u6309 F12 \u67e5\u770b\u3002<\/<\/span>p<\/span>><\/span><\/span><\/p>\n

      <<\/span>script<\/span>><\/span><\/span>
      \n \/\/ ===== \u6570\u636e\u533a =====<\/span>
      \n const<\/span> studentName =<\/span> "\u661f\u5b87"<\/span>;<\/span>
      \n const<\/span> score =<\/span> 78<\/span>;<\/span> \/\/ \u6570\u5b57，\u4e0d\u662f\u5b57\u7b26\u4e32\u2014\u201404 \u7bc7\u7684\u6559\u8bad\u8bb0\u4f4f\u4e86<\/span>
      \n const<\/span> attendance =<\/span> "\u5168\u52e4"<\/span>;<\/span> \/\/ \u8003\u52e4\u60c5\u51b5<\/span><\/p>\n

      \/\/ ===== \u5224\u5b9a\u533a：\u7b49\u7ea7\u94fe =====<\/span>
      \n let<\/span> grade;<\/span> \/\/ \u7b49\u7ea7\u8981\u5148\u7b97\u51fa\u6765，\u6240\u4ee5\u7528 let<\/span>
      \n if<\/span> (<\/span>score >=<\/span> 90<\/span>)<\/span> {<\/span>
      \n grade =<\/span> "\u4f18\u79c0"<\/span>;<\/span>
      \n }<\/span> else<\/span> if<\/span> (<\/span>score >=<\/span> 75<\/span>)<\/span> {<\/span>
      \n grade =<\/span> "\u826f\u597d"<\/span>;<\/span>
      \n }<\/span> else<\/span> if<\/span> (<\/span>score >=<\/span> 60<\/span>)<\/span> {<\/span>
      \n grade =<\/span> "\u53ca\u683c"<\/span>;<\/span>
      \n }<\/span> else<\/span> {<\/span>
      \n grade =<\/span> "\u4e0d\u53ca\u683c"<\/span>;<\/span>
      \n }<\/span><\/p>\n

      \/\/ \u590d\u5408\u6761\u4ef6：\u5956\u5b66\u91d1（&& \u6536\u7d27）<\/span>
      \n const<\/span> hasScholarship =<\/span> score >=<\/span> 90<\/span> &&<\/span> attendance ===<\/span> "\u5168\u52e4"<\/span>;<\/span><\/p>\n

      \/\/ ===== \u8f93\u51fa\u533a：\u6a21\u677f\u5b57\u7b26\u4e32 + \u4e09\u5143 =====<\/span>
      \n console.<\/span>log<\/span>(<\/span>"="<\/span>.<\/span>repeat<\/span>(<\/span>40<\/span>)<\/span>)<\/span>;<\/span>
      \n console.<\/span>log<\/span>(<\/span>" \u6210 \u7ee9 \u5224 \u5b9a \u62a5 \u544a"<\/span>)<\/span>;<\/span>
      \n console.<\/span>log<\/span>(<\/span>"="<\/span>.<\/span>repeat<\/span>(<\/span>40<\/span>)<\/span>)<\/span>;<\/span>
      \n console.<\/span>log<\/span>(<\/span>`<\/span>\u59d3\u540d：<\/span>${<\/span>studentName}<\/span><\/span>`<\/span><\/span>)<\/span>;<\/span>
      \n console.<\/span>log<\/span>(<\/span>`<\/span>\u5206\u6570：<\/span>${<\/span>score}<\/span><\/span>（\u7c7b\u578b <\/span>${<\/span>typeof<\/span> score}<\/span><\/span>，\u7eaf\u6570\u5b57）<\/span>`<\/span><\/span>)<\/span>;<\/span>
      \n console.<\/span>log<\/span>(<\/span>`<\/span>\u8003\u52e4：<\/span>${<\/span>attendance}<\/span><\/span>`<\/span><\/span>)<\/span>;<\/span>
      \n console.<\/span>log<\/span>(<\/span>`<\/span>\u7b49\u7ea7：<\/span>${<\/span>grade}<\/span><\/span>`<\/span><\/span>)<\/span>;<\/span>
      \n console.<\/span>log<\/span>(<\/span>`<\/span>\u7ed3\u8bba：<\/span>${<\/span>score >=<\/span> 60<\/span> ?<\/span> "\u672c\u5b66\u671f\u5e73\u5b89\u843d\u5730"<\/span> :<\/span> "\u5047\u671f\u89c4\u5212\u8865\u8003"<\/span>}<\/span><\/span>`<\/span><\/span>)<\/span>;<\/span>
      \n console.<\/span>log<\/span>(<\/span>`<\/span>\u5956\u5b66\u91d1：<\/span>${<\/span>hasScholarship ?<\/span> "\u7b26\u5408\u6761\u4ef6，\u53ef\u4ee5\u7533\u8bf7"<\/span> :<\/span> "\u6682\u4e0d\u7b26\u5408（\u9700 90 \u5206\u4ee5\u4e0a\u4e14\u5168\u52e4）"<\/span>}<\/span><\/span>`<\/span><\/span>)<\/span>;<\/span>
      \n console.<\/span>log<\/span>(<\/span>"="<\/span>.<\/span>repeat<\/span>(<\/span>40<\/span>)<\/span>)<\/span>;<\/span>
      \n <\/span><\/span><\/<\/span>script<\/span>><\/span><\/span>
      \n<\/<\/span>body<\/span>><\/span><\/span>
      \n<\/<\/span>html<\/span>><\/span><\/span><\/p>\n

      \u7559\u4e2a\u5fc3\u773c\u770b\u7ed3\u6784：\u6570\u636e\u533a \u2192 \u5224\u5b9a\u533a \u2192 \u8f93\u51fa\u533a，\u4e09\u6bb5\u5f0f\u548c 03 \u7bc7\u7684\u8d44\u6599\u5361\u4e00\u8109\u76f8\u627f\u2014\u2014\u4ee5\u540e\u6240\u6709\u5de5\u5177\u90fd\u662f"\u6570\u636e\u8fdb\u6765\u3001\u903b\u8f91\u52a0\u5de5\u3001\u62a5\u544a\u51fa\u53bb"，\u53ea\u662f\u6bcf\u6bb5\u4f1a\u8d8a\u957f\u8d8a\u58ee\u3002<\/p>\n

      \u4e94\u3001\u8fd0\u884c\u6548\u679c<\/h3>\n

      \"\u5728\u8fd9\u91cc\u63d2\u5165\u56fe\u7247\u63cf\u8ff0\"<\/p>\n

      ========================================
      \n \u6210 \u7ee9 \u5224 \u5b9a \u62a5 \u544a
      \n========================================
      \n\u59d3\u540d：\u661f\u5b87
      \n\u5206\u6570：78（\u7c7b\u578b number，\u7eaf\u6570\u5b57）
      \n\u8003\u52e4：\u5168\u52e4
      \n\u7b49\u7ea7：\u826f\u597d
      \n\u7ed3\u8bba：\u672c\u5b66\u671f\u5e73\u5b89\u843d\u5730
      \n\u5956\u5b66\u91d1：\u6682\u4e0d\u7b26\u5408（\u9700 90 \u5206\u4ee5\u4e0a\u4e14\u5168\u52e4）
      \n========================================<\/p>\n

      \u516d\u3001\u5e38\u89c1\u62a5\u9519\u4e0e\u6392\u67e5<\/h3>\n

      \u62a5\u9519 1：SyntaxError: Unexpected token 'else' \"\u5728\u8fd9\u91cc\u63d2\u5165\u56fe\u7247\u63cf\u8ff0\"<\/p>\n

      \u539f\u56e0：\u4e5d\u6210\u662f if \u90a3\u884c\u884c\u5c3e\u624b\u6ed1\u591a\u4e86\u5206\u53f7\u2014\u2014if (score >= 90); \u5206\u53f7\u628a if \u63d0\u524d"\u7ec8\u7ed3"，\u540e\u9762\u7684 else \u6210\u4e86\u5b64\u513f\u3002 \u89e3\u51b3：\u5220\u6389\u90a3\u4e2a\u5206\u53f7\u3002\u519b\u89c4：if \/ else \u884c\u5c3e\u6c38\u8fdc\u4e0d\u5199\u5206\u53f7（\u5206\u53f7\u5c5e\u4e8e\u5927\u62ec\u53f7\u91cc\u7684\u8bed\u53e5，\u4e0d\u5c5e\u4e8e if \u884c\u672c\u8eab）\u3002<\/p>\n

      \u73b0\u8c61 2：\u67d0\u4e2a\u5206\u652f\u6c38\u8fdc\u6267\u884c（\u6216\u6c38\u8fdc\u4e0d\u6267\u884c）<\/p>\n

      \u539f\u56e0：\u6761\u4ef6\u91cc\u5199\u4e86\u4e00\u4e2a\u7b49\u53f7\u2014\u2014if (score = 90) \u662f\u8d4b\u503c：\u628a 90 \u585e\u8fdb score，\u6574\u4e2a\u8868\u8fbe\u5f0f\u503c\u4e3a 90（truthy），\u6c38\u8fdc\u8d70 if \u5206\u652f，\u8fd8\u4e0d\u62a5\u4efb\u4f55\u9519\u3002 \u89e3\u51b3：\u6570\u4e00\u6570\u6761\u4ef6\u91cc\u7684\u7b49\u53f7\u6570\u91cf\u2014\u2014\u4e00\u4e2a = \u662f\u8d4b\u503c，=== \u624d\u662f\u6bd4\u8f83\u3002\u8fd9\u662f\u65b0\u624b\u903b\u8f91\u9b3c\u755c\u7b2c\u4e00\u540d，\u6bd4\u62a5\u9519\u66f4\u9634\u9669\u3002<\/p>\n

      \u73b0\u8c61 3："10" < "9" \u4e3a true<\/p>\n

      04 \u7bc7\u75ab\u82d7\u7684\u6b63\u5f0f\u7b54\u6848：\u4e24\u8fb9\u90fd\u662f\u5b57\u7b26\u4e32，\u6bd4\u8f83\u8d70\u5b57\u5178\u5e8f，\u9010\u5b57\u7b26\u6bd4\u5bf9\u3002 \u89e3\u51b3：\u6570\u5b57\u6bd4\u8f83\u524d\u5148 Number() \u6d17\u4e00\u904d，\u4fdd\u8bc1\u4e24\u8fb9\u90fd\u662f number\u3002<\/p>\n

      \u6392\u67e5\u5fc3\u6cd5：else \u62a5\u9519\u627e\u5206\u53f7，\u903b\u8f91\u9b3c\u755c\u6570\u7b49\u53f7，\u6bd4\u8f83\u79bb\u8c31\u67e5\u7c7b\u578b\u3002\u6761\u4ef6\u4e16\u754c\u7684\u4e09\u5927\u5751，\u4e00\u53e5\u8bdd\u6253\u5305\u3002<\/p>\n

      \u4e03\u3001\u7ec3\u4e60\u4f5c\u4e1a<\/h3>\n
    • \u624b\u52a8\u6a21\u62df（\u5148\u5199\u7b54\u6848\u518d\u56de\u8f66）："1" == 1\u3001"1" === 1\u3001null == undefined\u3001null === undefined\u30010 == false\u30010 === false \u5404\u5f97\u4ec0\u4e48？<\/li>\n
    • \u9884\u6d4b\u518d\u9a8c\u8bc1：const x = 0; \u4e4b\u540e\u6267\u884c if (x = 5) { console.log("A"); } else { console.log("B"); } \u8f93\u51fa\u4ec0\u4e48？x \u6700\u540e\u7684\u503c\u53d8\u6210\u4e86\u591a\u5c11？\u4e3a\u4ec0\u4e48？<\/li>\n
    • \u6539\u9020\u8981\u70b9：\u7ed9\u5224\u5b9a\u5668\u52a0"\u65f7\u8003"\u5206\u652f\u2014\u2014score === -1 \u8868\u793a\u65f7\u8003，\u7b49\u7ea7\u5224\u4e3a"\u65f7\u8003"\u3001\u7ed3\u8bba\u5224\u4e3a"\u9700\u8054\u7cfb\u6559\u52a1"；\u6ce8\u610f else if \u7684\u987a\u5e8f\u8be5\u63d2\u5728\u54ea（\u63d0\u793a：-1 < 60，\u653e\u6700\u524d\u9762\u5224\u65ad）；<\/li>\n
    • \u75ab\u82d7（\u4e0b\u7bc7\u9884\u544a）：\u73b0\u5728\u5224\u5b9a\u5668\u53ea\u80fd\u5224\u4e00\u4e2a\u5b66\u751f\u3002\u5168\u73ed 8 \u4e2a\u4eba\u30018 \u4e2a\u5206\u6570，\u96be\u9053\u628a\u5224\u5b9a\u533a\u590d\u5236 8 \u904d？\u7535\u8111\u6700\u64c5\u957f\u7684\u4e8b\u5c31\u662f\u91cd\u590d\u2014\u201406 \u7bc7\u7684\u5faa\u73af\u4e09\u884c\u4ee3\u7801\u5224 800 \u4eba\u3002\u52a8\u624b\u524d\u5148\u5728\u7eb8\u4e0a\u60f3：\u5224\u5b9a\u533a\u54ea\u4e9b\u884c\u662f"\u6bcf\u4e2a\u5b66\u751f\u90fd\u8981\u8dd1\u4e00\u904d"\u7684，\u54ea\u4e9b\u884c\u662f"\u5168\u73ed\u53ea\u9700\u8dd1\u4e00\u904d"\u7684？（\u8fd9\u4e2a\u601d\u8003\u5c31\u662f 07 \u7bc7\u51fd\u6570\u5316\u7684\u9884\u70ed\u3002）<\/li>\n
      \n

      \u4e0b\u4e00\u7bc7\u9884\u544a：\u300a06 \u5faa\u73af：\u8ba9\u7a0b\u5e8f\u91cd\u590d\u5e72\u6d3b\u300b\u2014\u2014for \u5faa\u73af\u4e09\u6bb5\u5f0f\u300102 \u7bc7\u624b\u5199\u7684\u661f\u661f\u6811\u4e09\u884c\u4ee3\u7801\u751f\u6210\u4e00\u767e\u5c42，\u8fd8\u6709 break\/continue \u4e24\u5f20"\u9003\u751f\u5238"\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"

      \u4e0a\u4e00\u7bc7：04 \u6570\u5b57\u4e0e\u5b57\u7b26\u4e32： \u53f7\u7684\u4e24\u526f\u9762\u5b54（\u62fc\u63a5\u4e0e\u76f8\u52a0 \u00b7 NaN \u00b7 \u7c7b\u578b\u4e92\u8f6c \u00b7 \u6a21\u677f\u5b57\u7b26\u4e32） \u4e0a\u7bc7\u7ec3\u4e60\u53c2\u8003\u7b54\u6848
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