{"id":2047,"date":"2024-05-28T23:42:18","date_gmt":"2024-05-28T15:42:18","guid":{"rendered":"https:\/\/zhuxinyong.com\/?p=2047"},"modified":"2024-05-28T23:43:10","modified_gmt":"2024-05-28T15:43:10","slug":"ts-as-vs-is","status":"publish","type":"post","link":"https:\/\/zhuxinyong.com\/?p=2047","title":{"rendered":"TS – as vs is"},"content":{"rendered":"

is<\/code> \u662f TypeScript \u4e2d\u7528\u4e8e\u7c7b\u578b\u65ad\u8a00\u7684\u5173\u952e\u5b57\uff0c\u5b83\u7528\u4e8e\u5728\u8fd0\u884c\u65f6\u5bf9\u503c\u7684\u7c7b\u578b\u8fdb\u884c\u5224\u65ad\u3002\u901a\u8fc7\u4f7f\u7528 is<\/code>\uff0c\u4f60\u53ef\u4ee5\u7f16\u5199\u81ea\u5b9a\u4e49\u7684\u7c7b\u578b\u4fdd\u62a4\u51fd\u6570\uff0c\u5e2e\u52a9 TypeScript \u7f16\u8bd1\u5668\u7406\u89e3\u4ee3\u7801\u4e2d\u53d8\u91cf\u7684\u7c7b\u578b\u3002\u4e0b\u9762\u662f is<\/code> \u7684\u8bed\u6cd5\u548c\u4e00\u4e2a\u7b80\u5355\u7684\u4f7f\u7528\u6848\u4f8b\uff1a<\/p>\n

<\/span><\/a>\u8bed\u6cd5<\/h3>\n
function isType(variable: any): variable is ExpectedType {\n  \/\/ \u68c0\u67e5 variable \u662f\u5426\u4e3a ExpectedType \u7c7b\u578b\u7684\u503c\n  \/\/ \u8fd4\u56de\u503c\u4e3a\u5e03\u5c14\u7c7b\u578b\uff0c\u6307\u793a variable \u662f\u5426\u4e3a ExpectedType \u7c7b\u578b\n}\n<\/code><\/pre>\n
<\/span><\/a>\u4f7f\u7528\u6848\u4f8b<\/h3>\n
\u5047\u8bbe\u6211\u4eec\u6709\u4e00\u4e2a User<\/code> \u7c7b\u578b\u548c\u4e00\u4e2a isAdmin<\/code> \u51fd\u6570\uff0c\u7528\u4e8e\u5224\u65ad\u7528\u6237\u662f\u5426\u4e3a\u7ba1\u7406\u5458\u3002\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528 is<\/code> \u5173\u952e\u5b57\u521b\u5efa\u4e00\u4e2a\u7c7b\u578b\u4fdd\u62a4\u51fd\u6570\u6765\u544a\u8bc9 TypeScript \u7f16\u8bd1\u5668\uff0c\u5f53 user<\/code> \u4e3a\u7ba1\u7406\u5458\u65f6\uff0c\u5b83\u662f\u4e00\u4e2a AdminUser<\/code> \u7c7b\u578b\u7684\u503c\u3002<\/p>\n
interface User {\n  name: string;\n  isAdmin: boolean;\n}\n\ninterface AdminUser extends User {\n  privileges: string[];\n}\n\nfunction isAdmin(user: User): user is AdminUser {\n  return user.isAdmin === true;\n}\n\n\/\/ \u4f7f\u7528 isAdmin \u51fd\u6570\u8fdb\u884c\u7c7b\u578b\u4fdd\u62a4\nfunction printUserInfo(user: User) {\n  if (isAdmin(user)) {\n    console.log(`${user.name} is an admin with privileges: ${user.privileges.join(', ')}`);\n  } else {\n    console.log(`${user.name} is not an admin.`);\n  }\n}\n<\/code><\/pre>\n
\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0cisAdmin<\/code> \u51fd\u6570\u63a5\u6536\u4e00\u4e2a User<\/code> \u7c7b\u578b\u7684\u53c2\u6570\uff0c\u5e76\u8fd4\u56de\u4e00\u4e2a\u5e03\u5c14\u503c\u3002\u5f53\u7528\u6237\u662f\u7ba1\u7406\u5458\u65f6\uff0c\u5b83\u8fd4\u56de true<\/code>\uff0c\u8868\u793a\u7528\u6237\u662f AdminUser<\/code> \u7c7b\u578b\u7684\u503c\uff1b\u5426\u5219\u8fd4\u56de false<\/code>\u3002\u5728 printUserInfo<\/code> \u51fd\u6570\u4e2d\uff0c\u6211\u4eec\u4f7f\u7528 isAdmin<\/code> \u51fd\u6570\u5bf9 user<\/code> \u53d8\u91cf\u8fdb\u884c\u7c7b\u578b\u4fdd\u62a4\uff0c\u6839\u636e\u5176\u8fd4\u56de\u503c\u7684\u7c7b\u578b\u6765\u6267\u884c\u4e0d\u540c\u7684\u903b\u8f91\u3002\u8fd9\u6837\uff0cTypeScript \u7f16\u8bd1\u5668\u80fd\u591f\u6b63\u786e\u5730\u63a8\u65ad\u51fa user<\/code> \u5728\u4e0d\u540c\u5206\u652f\u4e2d\u7684\u7c7b\u578b\uff0c\u5e76\u6267\u884c\u7c7b\u578b\u68c0\u67e5\u3002<\/p>\n
as<\/code> \u662f TypeScript \u4e2d\u7684\u7c7b\u578b\u65ad\u8a00\u5173\u952e\u5b57\uff0c\u7528\u4e8e\u624b\u52a8\u6307\u5b9a\u4e00\u4e2a\u503c\u7684\u7c7b\u578b\u3002\u5b83\u53ef\u4ee5\u7528\u4e8e\u7c7b\u578b\u8f6c\u6362\uff0c\u544a\u8bc9 TypeScript \u7f16\u8bd1\u5668\u5728\u7f16\u8bd1\u65f6\u5c06\u4e00\u4e2a\u503c\u89c6\u4e3a\u7279\u5b9a\u7684\u7c7b\u578b\u3002\u4e0b\u9762\u662f as<\/code> \u7684\u8bed\u6cd5\u548c\u4e00\u4e2a\u7b80\u5355\u7684\u4f7f\u7528\u6848\u4f8b\uff1a<\/p>\n
<\/span><\/a>\u8bed\u6cd5<\/h3>\n
const variableName = value as TypeName;\n<\/code><\/pre>\n
\u6216\u8005<\/p>\n
const variableName = <TypeName>value;\n<\/code><\/pre>\n
<\/span><\/a>\u4f7f\u7528\u6848\u4f8b<\/h3>\n
\u5047\u8bbe\u6211\u4eec\u4ece\u540e\u7aef API \u4e2d\u83b7\u53d6\u4e00\u4e2a JSON \u6570\u636e\uff0c\u5e76\u4e14\u6211\u4eec\u77e5\u9053\u8be5\u6570\u636e\u7684\u7ed3\u6784\u3002\u4f46\u7531\u4e8e\u7f51\u7edc\u8bf7\u6c42\u7684\u4e0d\u786e\u5b9a\u6027\uff0cTypeScript \u7f16\u8bd1\u5668\u65e0\u6cd5\u51c6\u786e\u5730\u63a8\u65ad\u51fa\u83b7\u53d6\u7684\u6570\u636e\u7684\u7c7b\u578b\u3002\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528 as<\/code> \u8fdb\u884c\u7c7b\u578b\u65ad\u8a00\uff0c\u544a\u8bc9 TypeScript \u7f16\u8bd1\u5668\u5c06\u83b7\u53d6\u7684\u6570\u636e\u89c6\u4e3a\u7279\u5b9a\u7684\u7c7b\u578b\u3002<\/p>\n
interface UserData {\n  id: number;\n  name: string;\n  email: string;\n}\n\nfunction fetchUserData(): any {\n  \/\/ \u6a21\u62df\u4ece\u540e\u7aef API \u83b7\u53d6\u6570\u636e\n  return {\n    id: 1,\n    name: 'Alice',\n    email: 'alice@example.com'\n  };\n}\n\nconst userData = fetchUserData() as UserData;\n\n\/\/ \u73b0\u5728 TypeScript \u7f16\u8bd1\u5668\u77e5\u9053 userData \u662f\u4e00\u4e2a UserData \u7c7b\u578b\u7684\u5bf9\u8c61\nconsole.log(userData.id);    \/\/ \u6b63\u786e\uff1a\u7f16\u8bd1\u5668\u77e5\u9053 userData \u6709 id \u5c5e\u6027\nconsole.log(userData.name);  \/\/ \u6b63\u786e\uff1a\u7f16\u8bd1\u5668\u77e5\u9053 userData \u6709 name \u5c5e\u6027\nconsole.log(userData.email); \/\/ \u6b63\u786e\uff1a\u7f16\u8bd1\u5668\u77e5\u9053 userData \u6709 email \u5c5e\u6027\n\/\/ console.log(userData.age); \/\/ \u9519\u8bef\uff1a\u7f16\u8bd1\u5668\u77e5\u9053 userData \u6ca1\u6709 age \u5c5e\u6027\n<\/code><\/pre>\n
\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0c\u6211\u4eec\u4f7f\u7528 as UserData<\/code> \u5c06 fetchUserData()<\/code> \u7684\u8fd4\u56de\u503c\u65ad\u8a00\u4e3a UserData<\/code> \u7c7b\u578b\u3002\u8fd9\u6837\u4e00\u6765\uff0cTypeScript \u7f16\u8bd1\u5668\u5c31\u80fd\u591f\u6b63\u786e\u5730\u63a8\u65ad\u51fa userData<\/code> \u7684\u7c7b\u578b\uff0c\u5e76\u4e14\u53ef\u4ee5\u5728\u540e\u7eed\u4ee3\u7801\u4e2d\u5b89\u5168\u5730\u4f7f\u7528\u8be5\u5bf9\u8c61\u7684\u5c5e\u6027\u3002<\/p>\n
\u5728TypeScript\u4e2d\uff0cas<\/code>\u548cis<\/code>\u662f\u4e24\u79cd\u4e0d\u540c\u7684\u7c7b\u578b\u65ad\u8a00\u65b9\u5f0f\uff0c\u5b83\u4eec\u5728\u4f7f\u7528\u573a\u666f\u548c\u8bed\u4e49\u4e0a\u6709\u6240\u4e0d\u540c\u3002<\/p>\n
<\/span><\/a>as<\/code> \u7c7b\u578b\u65ad\u8a00<\/h3>\n
as<\/code> \u7c7b\u578b\u65ad\u8a00\u662fTypeScript\u4e2d\u7528\u4e8e\u7c7b\u578b\u8f6c\u6362\u7684\u8bed\u6cd5\u3002\u5b83\u5141\u8bb8\u4f60\u5c06\u4e00\u4e2a\u8868\u8fbe\u5f0f\u7684\u7c7b\u578b\u65ad\u8a00\u4e3a\u53e6\u4e00\u4e2a\u7c7b\u578b\u3002\u8fd9\u79cd\u65ad\u8a00\u5728TypeScript\u7f16\u8bd1\u5668\u4e2d\u4e0d\u4f1a\u8fdb\u884c\u7c7b\u578b\u68c0\u67e5\uff0c\u5b83\u544a\u8bc9\u7f16\u8bd1\u5668\u4f60\u5df2\u7ecf\u77e5\u9053\u8868\u8fbe\u5f0f\u7684\u7c7b\u578b\uff0c\u5e76\u4e14\u4f60\u5e0c\u671b\u7f16\u8bd1\u5668\u6309\u7167\u4f60\u6307\u5b9a\u7684\u7c7b\u578b\u6765\u5904\u7406\u8fd9\u4e2a\u8868\u8fbe\u5f0f\u3002<\/p>\n
let someValue: any = "this is a string";\n\n\/\/ \u4f7f\u7528 as \u7c7b\u578b\u65ad\u8a00\nlet strLength: number = (someValue as string).length;\n<\/code><\/pre>\n
\u5728\u4e0a\u9762\u7684\u4f8b\u5b50\u4e2d\uff0c\u6211\u4eec\u4f7f\u7528as<\/code>\u65ad\u8a00\u5c06someValue<\/code>\u7684\u7c7b\u578b\u4eceany<\/code>\u65ad\u8a00\u4e3astring<\/code>\uff0c\u7136\u540e\u8bbf\u95eelength<\/code>\u5c5e\u6027\u3002<\/p>\n
<\/span><\/a>is<\/code> \u7c7b\u578b\u5b88\u536b<\/h3>\n
is<\/code> \u7c7b\u578b\u5b88\u536b\u662fTypeScript\u4e2d\u7528\u4e8e\u7c7b\u578b\u68c0\u67e5\u7684\u8bed\u6cd5\u3002\u5b83\u901a\u5e38\u4e0e\u51fd\u6570\u4e00\u8d77\u4f7f\u7528\uff0c\u7528\u4e8e\u5728\u8fd0\u884c\u65f6\u68c0\u67e5\u4e00\u4e2a\u503c\u662f\u5426\u7b26\u5408\u67d0\u4e2a\u7279\u5b9a\u7684\u7c7b\u578b\u3002is<\/code>\u5173\u952e\u5b57\u540e\u9762\u8ddf\u7684\u662f\u4e00\u4e2a\u7c7b\u578b\u8c13\u8bcd\uff0c\u5b83\u544a\u8bc9\u7f16\u8bd1\u5668\u5982\u679c\u6761\u4ef6\u4e3a\u771f\uff0c\u5219\u8868\u8fbe\u5f0f\u7684\u7c7b\u578b\u4e3a\u6307\u5b9a\u7684\u7c7b\u578b\u3002<\/p>\n
function isString(value: any): value is string {\n  return typeof value === "string";\n}\n\nfunction processValue(value: any) {\n  if (isString(value)) {\n    \/\/ \u5728\u8fd9\u91cc\uff0cTypeScript\u7f16\u8bd1\u5668\u77e5\u9053value\u662fstring\u7c7b\u578b\n    console.log(value.toUpperCase());\n  } else {\n    \/\/ \u5728\u8fd9\u91cc\uff0cTypeScript\u7f16\u8bd1\u5668\u77e5\u9053value\u4e0d\u662fstring\u7c7b\u578b\n    console.log(value.toFixed());\n  }\n}\n<\/code><\/pre>\n
\u5728\u4e0a\u9762\u7684\u4f8b\u5b50\u4e2d\uff0cisString<\/code>\u51fd\u6570\u662f\u4e00\u4e2a\u7c7b\u578b\u5b88\u536b\u51fd\u6570\uff0c\u5b83\u8fd4\u56de\u4e00\u4e2a\u5e03\u5c14\u503c\uff0c\u8868\u793a\u4f20\u5165\u7684\u503c\u662f\u5426\u4e3a\u5b57\u7b26\u4e32\u7c7b\u578b\u3002\u5728processValue<\/code>\u51fd\u6570\u4e2d\uff0c\u6211\u4eec\u4f7f\u7528isString<\/code>\u51fd\u6570\u6765\u68c0\u67e5value<\/code>\u7684\u7c7b\u578b\uff0c\u5e76\u636e\u6b64\u6267\u884c\u4e0d\u540c\u7684\u64cd\u4f5c\u3002<\/p>\n
\u603b\u7ed3\u6765\u8bf4\uff0cas<\/code>\u7c7b\u578b\u65ad\u8a00\u7528\u4e8e\u5728\u7f16\u8bd1\u65f6\u544a\u8bc9TypeScript\u7f16\u8bd1\u5668\u4e00\u4e2a\u8868\u8fbe\u5f0f\u7684\u7c7b\u578b\uff0c\u800cis<\/code>\u7c7b\u578b\u5b88\u536b\u7528\u4e8e\u5728\u8fd0\u884c\u65f6\u68c0\u67e5\u4e00\u4e2a\u503c\u7684\u7c7b\u578b\u3002\u5728\u4f7f\u7528\u65f6\uff0c\u5e94\u6839\u636e\u5177\u4f53\u9700\u6c42\u9009\u62e9\u5408\u9002\u7684\u65b9\u5f0f\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
is \u662f TypeScript \u4e2d\u7528\u4e8e\u7c7b\u578b\u65ad\u8a00\u7684\u5173\u952e\u5b57\uff0c\u5b83\u7528\u4e8e\u5728\u8fd0\u884c\u65f6\u5bf9\u503c\u7684\u7c7b\u578b\u8fdb\u884c\u5224\u65ad\u3002\u901a\u8fc7\u4f7f\u7528 ...<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[20,3],"tags":[33],"class_list":["post-2047","post","type-post","status-publish","format-standard","hentry","category-frontend","category-tech","tag-typescript"],"_links":{"self":[{"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/posts\/2047","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=2047"}],"version-history":[{"count":1,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/posts\/2047\/revisions"}],"predecessor-version":[{"id":2048,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/posts\/2047\/revisions\/2048"}],"wp:attachment":[{"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2047"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2047"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2047"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}