{"id":1260,"date":"2022-06-05T22:11:10","date_gmt":"2022-06-05T14:11:10","guid":{"rendered":"http:\/\/zhuxinyong.com\/?p=1260"},"modified":"2023-02-16T14:43:58","modified_gmt":"2023-02-16T06:43:58","slug":"31-ke-xuan-lian","status":"publish","type":"post","link":"https:\/\/zhuxinyong.com\/?p=1260","title":{"rendered":"31 – \u53ef\u9009\u94fe"},"content":{"rendered":"

\"\"<\/p>\n

\u539f\u6587\u5730\u5740\uff1ahttps:\/\/dev.to\/bhagatparwinder\/optional-chaining-1a1f<\/a><\/p>\n

<\/span><\/a>\u7b80\u4ecb<\/h2>\n

JavaScript \u4e2d\u83b7\u53d6\u5bf9\u8c61\u5c5e\u6027\u662f\u4e00\u4e2a\u5e38\u89c1\u64cd\u4f5c\uff0c\u591a\u6570\u65f6\u5019\u8fd9\u4e9b\u5c5e\u6027\u662f\u5d4c\u5957\u7684\u3002\u5f53\u4f60\u4ece\u4e00\u4e2a\u4e0d\u5b58\u5728\u7684\u5bf9\u8c61\u4e0a\u83b7\u53d6\u5c5e\u6027\u7684\u65f6\u5019\uff0cJavaScript \u5c31\u4f1a\u62a5\u9519\u3002<\/p>\n

\u8ba9\u6211\u4eec\u6765\u4e3e\u4e00\u4e9b\u4f8b\u5b50\u6765\u5e2e\u52a9\u7406\u89e3\uff1a<\/p>\n

const myObject = {\n    name: "Parwinder",\n    car: "Cybertruck",\n    age: 42,\n    computers: {\n        first: {\n            name: "iMac",\n            year: 2017,\n            spec: {\n                cpu: "i7",\n                ram: "16GB"\n            }\n        },\n        second: {\n            name: "MacBook Pro"\n        }\n    }\n}\n\nconsole.log(myObject.computers.first.spec.cpu); \/\/ i7\nconsole.log(myObject.computers.second.spec.cpu); \/\/ Cannot read property 'cpu' of undefined\n<\/code><\/pre>\n
\u7b2c\u4e00\u6761\u65e5\u5fd7\u901a\u8fc7\u5de1\u67e5\u5bf9\u8c61\u6765\u83b7\u53d6\u6211\u7b2c\u4e00\u53f0\u7535\u8111\u4e0a\u7684 CPU\uff0c\u5f53\u540c\u6837\u7684\u65b9\u6cd5\u7528\u5728\u7b2c\u4e8c\u53f0\u7535\u8111\u4e0a\u65f6\u5c31\u62a5\u9519\u3002<\/p>\n
\u5f53 spec \u4e0d\u5b58\u5728\u65f6\u6211\u4eec\u4f9d\u65e7\u5728\u5c1d\u8bd5\u83b7\u53d6 spec \u4e0a\u7684 cpu\uff0ccpu \u5728\u5bf9\u8c61\u7684\u7b2c\u4e94\u5c42\u5b83\u524d\u9762\u7684\u4efb\u4f55\u4e00\u5c42\u90fd\u6709\u53ef\u80fd\u4e3a null \u6216 undefined\u3002<\/p>\n
\u6211\u4eec\u901a\u8fc7 if \u8bed\u53e5\u914d\u5408 && \u64cd\u4f5c\u7b26\u6765\u89e3\u51b3\u6b64\u95ee\u9898\uff1a<\/p>\n
if(myObject && myObject.computers && myObject.computers.second && myObject.computers.second.spec) {\n    console.log(myObject.computers.second.spec.cpu);\n}\n<\/code><\/pre>\n
\u53ca\u65f6\u4e0a\u9762\u7684\u811a\u672c\u53ef\u4ee5\u6b63\u786e\u8fd0\u884c\uff0c\u4f46\u4ee3\u7801\u4e0d\u591f\u6574\u6d01\u3002\u6709\u592a\u591a\u7684\u4ee3\u7801\u6765\u6821\u9a8c null \/ undefined \u3002<\/p>\n
\u53ef\u9009\u94fe\u901a\u8fc7 ?.<\/code> \u6765\u8868\u793a\uff0c\u5b83\u53ef\u4ee5\u7528\u4e8e\u5bf9\u8c61\u4e0a\u7684\u952e\u548c\u8868\u8fbe\u5f0f\u3001\u6570\u7ec4\u7d22\u5f15\u4ee5\u53ca\u5bf9\u8c61\u4e0a\u7684\u51fd\u6570\u3002<\/p>\n
<\/span><\/a>\u5bf9\u8c61\u7684\u5c5e\u6027\u5e94\u7528\u53ef\u9009\u94fe<\/h2>\n
\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528\u53ef\u9009\u94fe\u6765\u91cd\u5199\u4e0a\u9762\u7684 if \u8bed\u53e5\uff1a<\/p>\n
myObject?.computers?.second?.spec?.cpu \/\/ undefined\n\n\/\/ Concise and easy to read code\n\/\/ or\n\nmyObject.computers.second.spec?.cpu\n<\/code><\/pre>\n
?.<\/code> \u64cd\u4f5c\u7b26\u53ef\u4ee5\u628a\u5bf9\u8c61\u4e0a\u7684\u5c5e\u6027\u8fdb\u884c\u77ed\u8def\u6c42\u503c\u3002\u53ef\u9009\u94fe\u4e0d\u662f\u901a\u8fc7\u7ee7\u7eed\u6c42\u503c\u6765\u8fd4\u56de\u9519\u8bef\uff0c\u800c\u662f\u4e00\u65e6\u53d1\u73b0\u94fe\u4e2d\u7684\u7b2c\u4e00\u4e2a undefined \u6216 null\uff0c\u5c31\u7acb\u5373\u7ec8\u6b62\uff0c\u5e76\u8fd4\u56de undefined\u3002<\/p>\n
?.<\/code> \u53ea\u5728\u5b83\u4f7f\u7528\u7684\u5730\u65b9\u8d77\u4f5c\u7528\u3002<\/p>\n
\u5728 myObject.computers.second.spec?.cpu<\/code> \u4e2d\u7684\u524d\u4e09\u4e2a\u5c5e\u6027\u90fd\u5fc5\u987b\u5b58\u5728\uff0c\u8fd9\u91cc\u53ea\u6709 spec<\/code> \u5f15\u7528\u4e86\u53ef\u9009\u94fe\uff0c\u82e5 spec<\/code> \u4e0d\u5b58\u5728\u624d\u8fd4\u56de undefined<\/code>\u3002<\/p>\n
\u524d\u9762\u4e09\u4e2a\u4efb\u4f55\u4e00\u4e2a\u5c5e\u6027\u7f3a\u5931\u90fd\u4f1a\u62a5\u9519\uff0c\u6240\u4ee5\u53ea\u5728\u5c5e\u6027\u53ef\u80fd\u5b58\u5728\u6216\u4e0d\u5b58\u5728\u7684\u5730\u65b9\u4f7f\u7528?.<\/code>\u3002\u82e5\u4ee3\u7801\u4e2d\u5404\u5904\u4f7f\u7528\u4f1a\u5bfc\u81f4\u9759\u9ed8\u5931\u8d25\u800c\u4e14\u5f88\u96be\u5b9a\u4f4d\u8c03\u8bd5\u3002<\/p>\n
\u4f8b\u5982\uff1a\u82e5 computers<\/code> \u662f\u53ef\u9009\u7684\uff0c\u4f46\u662f myObject<\/code> \u662f\u4e00\u5b9a\u4f1a\u5b58\u5728\u7684\uff0c\u90a3\u5e94\u8be5\u5199\u6210\u4e0b\u9762\uff1a<\/p>\n
myObject.computers?.\n<\/code><\/pre>\n
\u800c\u4e0d\u662f\uff1a<\/p>\n
myObject?.computers?.\n<\/code><\/pre>\n
<\/span><\/a>\u5bf9\u8c61\u7684\u8868\u8fbe\u5f0f\u5e94\u7528\u53ef\u9009\u94fe<\/h2>\n
\u6211\u4eec\u5728\u901a\u8fc7\u5b57\u9762\u91cf\u6216\u4e2d\u62ec\u53f7\u6765\u83b7\u53d6\u5bf9\u8c61\u5c5e\u6027\u65f6\u4f9d\u65e7\u53ef\u4ee5\u4f7f\u7528\u53ef\u9009\u94fe\u3002<\/p>\n
console.log(myObject.computers.second?.["spec"].cpu); \/\/ undefined\nconsole.log(myObject.computers.first?.["spec"].cpu); \/\/ i7\n<\/code><\/pre>\n
<\/span><\/a>\u5bf9\u8c61\u7684\u51fd\u6570\u5e94\u7528\u53ef\u9009\u94fe<\/h2>\n
\u6211\u4eec\u5728\u5bf9\u8c61\u4e0a\u6dfb\u52a0\u4e00\u4e2a\u51fd\u6570\uff1a<\/p>\n
const myObject = {\n    name: "Parwinder",\n    car: "Cybertruck",\n    age: 42,\n    getAge: function () {\n        return this.age;\n    }\n}\n\nconsole.log(myObject.getAge()); \/\/ 42\n<\/code><\/pre>\n
\u5982\u679c\u51fd\u6570\u662f\u53ef\u9009\u7684\uff0c\u6211\u4eec\u53ef\u4ee5\u52a0\u5165\u53ef\u9009\u94fe\u3002<\/p>\n
console.log(myObject.getAge?.());\n<\/code><\/pre>\n
\u53ef\u9009\u94fe\u4f1a\u786e\u4fdd JavaScript \u89c6\u56fe\u6267\u884c\u4e00\u4e2a\u4e0d\u5b58\u5728\u7684\u51fd\u6570\uff0c\u4f46\u7531\u4e8e ?.<\/code> \u63d0\u4f9b\u7684\u77ed\u8def\u64cd\u4f5c\u5b9e\u9645\u4e0a\u8c03\u7528\u6c38\u8fdc\u4e0d\u4f1a\u53d1\u751f\u3002<\/p>\n
<\/span><\/a>\u5bf9\u8c61\u4e0a\u7684\u6570\u7ec4\u5e94\u7528\u53ef\u9009\u94fe<\/h2>\n
const names = ["Parwinder", "Lauren", "Leah", "Robert", "Eliu"];\nconsole.log(names[3]); \/\/ Robert\n\nconst newEmployee = names?.[3]; \/\/ Check if names exists\nconsole.log(newEmployee); \/\/ Robert\n<\/code><\/pre>\n
\u6ce8\u610f\uff1a\u53ef\u9009\u94fe\u4e0d\u80fd\u5e94\u7528\u5728\u8d4b\u503c\u7684\u5de6\u4fa7\u3002<\/p>\n
let myObject = {};\nmyObject?.name = "Parwinder"; \/\/ Uncaught SyntaxError\n<\/code><\/pre>\n
\"\u524d\u7aef\u9ed1\u677f\u62a5\"<\/p>\n","protected":false},"excerpt":{"rendered":"
\u539f\u6587\u5730\u5740\uff1ahttps:\/\/dev.to\/bhagatparwinder\/optional-chain...<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[249,2,20,3],"tags":[141,140],"class_list":["post-1260","post","type-post","status-publish","format-standard","hentry","category-javascript","category-all","category-frontend","category-tech","tag-optional-chaining","tag-140"],"_links":{"self":[{"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/posts\/1260","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1260"}],"version-history":[{"count":1,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/posts\/1260\/revisions"}],"predecessor-version":[{"id":1261,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/posts\/1260\/revisions\/1261"}],"wp:attachment":[{"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1260"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1260"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1260"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}