\u6211\u76f8\u4fe1\u5b66\u4e60\u65b0\u4e8b\u7269\u5e76\u8bc4\u4f30\u6211\u4eec\u6240\u77e5\u7684\u4e1c\u897f\u5bf9\u81ea\u5df1\u7684\u8fdb\u6b65\u975e\u5e38\u6709\u7528\uff0c\u53ef\u4ee5\u907f\u514d\u4e86\u6211\u4eec\u89c9\u5f97\u81ea\u5df1\u7684\u77e5\u8bc6\u8fc7\u65f6\u7684\u60c5\u51b5\u3002\u5728\u672c\u6587\u4e2d\uff0c\u6211\u5c06\u4ecb\u7ecd\u4e00\u4e9b\u5e38\u89c1\u7684 JavaScript \u77e5\u8bc6\u3002\u8bf7\u4eab\u7528!<\/p>\n

1.\u58f0\u660e<\/strong><\/span><\/div>\n
\u67e5\u770b\u4ee5\u4e0b\u4ee3\u7801\uff0c\u5e76\u56de\u7b54\u8f93\u51fa\u7684\u5185\u5bb9(\u4ee5\u53ca\u539f\u56e0)\u3002<\/p>\n
\/\/ situation 1 \r\nconsole.log(person); \r\nvar person = 'John'; \r\n \r\n\/\/ situation 2 \r\nconsole.log(person); \r\nlet person = 'Phill'; \r\n \r\n\/\/ situation 3 \r\nconsole.log(person); \r\nconst person = 'Frank'; \r\n \r\n\/\/ situation 4 \r\nconst person = 'Vanessa'; \r\nconsole.log(person); \r\nperson = 'Mike'; \r\nconsole.log(person); \r\n \r\n\/\/ situation 5 \r\nvar person = 'John'; \r\nlet person = 'Mike'; \r\nconsole.log(person); \r\n \r\n\/\/ situation 6 \r\nvar person = 'John'; \r\nif (person) { \r\n let person = 'Mike'; \r\n console.log(person); \r\n} \r\nconsole.log(person); \r\n<\/pre>\n
\u8bf4\u660e
\nSituation 1: \u9884\u671f\u7ed3\u679c\u662f\u5728\u63a7\u5236\u53f0\u4e2d\u770b\u5230\u6587\u672c John\uff0c\u4f46\u662f\u4ee4\u4eba\u60ca\u8bb6\u7684\u662f\uff0c\u6211\u4eec\u770b\u5230\u8bb0\u5f55\u4e86undefined\u3002\u60f3\u77e5\u9053\u4e3a\u4ec0\u4e48\u5417?
\n\u597d\u5427\uff0c\u8fd9\u662f\u7ecf\u5178\u7684 JavaScript \u5728\u8d77\u4f5c\u7528\u3002\u8fd9\u79cd\u884c\u4e3a\u88ab\u79f0\u4e3a\u63d0\u5347\u3002\u5728\u540e\u53f0\uff0c\u8be5\u8bed\u8a00\u5c06\u53d8\u91cf\u58f0\u660e\u548c\u503c\u5206\u914d\u5206\u4e3a\u4e24\u90e8\u5206\u3002\u4e0d\u7ba1\u53d8\u91cf\u6700\u521d\u7531\u5f00\u53d1\u4eba\u5458\u5728\u54ea\u91cc\u58f0\u660e\uff0c\u53d8\u91cf\u90fd\u5c06\u79fb\u52a8\u5230\u9876\u90e8\uff0c\u58f0\u660e\u65f6\u5c06\u5176\u503c\u8bbe\u7f6e\u4e3a undefined\u3002\u770b\u8d77\u6765\u50cf\u8fd9\u6837\uff1a<\/p>\n
var person; \r\nconsole.log(person); \r\nperson = 'John'; \r\n<\/pre>\n
Situation 2: \u5728\u8fd9\u91cc\uff0c\u7ed3\u679c\u5c06\u662f\u5f15\u7528\u9519\u8bef\u3002<\/p>\n
Uncaught ReferenceError: Cannot access 'person' before initialization \r\n<\/pre>\n
\u9519\u8bef\u6587\u672c\u8bf4\u660e\u4e86\u4e00\u5207\u3002\u56e0\u4e3a\u6211\u4eec\u4f7f\u7528\u4e86\u5173\u952e\u5b57 let\uff0c\u6240\u4ee5\u6211\u4eec\u7684\u53d8\u91cf\u88ab\u63d0\u5347\uff0c\u4f46\u6ca1\u6709\u521d\u59cb\u5316\uff0c\u5e76\u4e14\u629b\u51fa\u8be5\u9519\u8bef\uff0c\u901a\u77e5\u6211\u4eec\u6b63\u5728\u5c1d\u8bd5\u8bbf\u95ee\u672a\u521d\u59cb\u5316\u7684\u53d8\u91cf\u3002\u5728 ES6 \u4e2d\u5f15\u5165\u4e86\u5173\u952e\u5b57 let\uff0c\u4f7f\u6211\u4eec\u80fd\u591f\u4f7f\u7528\u5757\u4f5c\u7528\u57df\u4e2d\u7684\u53d8\u91cf\uff0c\u4ece\u800c\u5e2e\u52a9\u6211\u4eec\u9632\u6b62\u610f\u5916\u884c\u4e3a\u3002
\n\u5728\u8fd9\u91cc\uff0c\u6211\u4eec\u4f1a\u5f97\u5230\u4e0e Situation 2 \u4e2d\u76f8\u540c\u7684\u9519\u8bef\u3002
\n\u4e0d\u540c\u4e4b\u5904\u5728\u4e8e\u6211\u4eec\u4f7f\u7528\u4e86\u5173\u952e\u5b57 const\uff0c\u4ece\u800c\u9632\u6b62\u5728\u521d\u59cb\u5316\u540e\u91cd\u65b0\u5206\u914d\u53d8\u91cf\u3002 ES6 \u4e2d\u4e5f\u5f15\u5165\u4e86\u6b64\u5173\u952e\u5b57\u3002
\nSituation 4: \u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u6211\u4eec\u53ef\u4ee5\u770b\u5230\u5173\u952e\u5b57 const \u662f\u5982\u4f55\u5de5\u4f5c\u7684\uff0c\u4ee5\u53ca\u5b83\u5982\u4f55\u907f\u514d\u65e0\u610f\u4e2d\u91cd\u65b0\u5206\u914d\u53d8\u91cf\u3002\u5728\u6211\u4eec\u7684\u793a\u4f8b\u4e2d\uff0c\u9996\u5148\u4f1a\u5728\u63a7\u5236\u53f0\u4e2d\u770b\u5230 Vanessa\uff0c\u7136\u540e\u662f\u4e00\u4e2a\u7c7b\u578b\u9519\u8bef\u3002<\/p>\n
Uncaught TypeError: Assignment to constant variable \r\n<\/pre>\n
const \u53d8\u91cf\u7684\u4f7f\u7528\u968f\u7740\u6211\u4eec\u7684\u4ee3\u7801\u5e93\u5448\u6307\u6570\u589e\u957f\u3002
\nSituation 5: \u5982\u679c\u5df2\u7ecf\u5728\u67d0\u4e2a\u4f5c\u7528\u57df\u5185\u4f7f\u7528\u5173\u952e\u5b57 var \u5b9a\u4e49\u4e86\u53d8\u91cf\uff0c\u5219\u5728\u540c\u4e00\u4f5c\u7528\u57df\u4e2d\u7528\u5173\u952e\u5b57 let \u518d\u6b21\u58f0\u660e\u8be5\u53d8\u91cf\u5c06\u4f1a\u5f15\u53d1\u9519\u8bef\u3002
\n\u56e0\u6b64\uff0c\u5728\u6211\u4eec\u7684\u793a\u4f8b\u4e2d\uff0c\u5c06\u4e0d\u4f1a\u8f93\u51fa\u4efb\u4f55\u5185\u5bb9\uff0c\u5e76\u4e14\u4f1a\u770b\u5230\u8bed\u6cd5\u9519\u8bef\u63d0\u793a\u3002<\/p>\n
Uncaught SyntaxError: Identifier 'person' has already been declared \r\n<\/pre>\n
Situation 6: \u6211\u4eec\u5206\u522b\u6709\u4e00\u4e2a\u51fd\u6570\u4f5c\u7528\u57df\u7684\u53d8\u91cf\uff0c\u548c\u5757\u4f5c\u7528\u57df\u7684\u53d8\u91cf\u3002\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u5b83\u4eec\u662f\u5426\u6709\u76f8\u540c\u7684\u540d\u5b57\u6216\u6807\u8bc6\u7b26\u5e76\u4e0d\u91cd\u8981\u3002
\n\u5728\u63a7\u5236\u53f0\u4e2d\uff0c\u6211\u4eec\u5e94\u8be5\u770b\u5230 Mike \u548c John \u88ab\u4f9d\u6b21\u8f93\u51fa\u3002\u4e3a\u4ec0\u4e48?
\n\u56e0\u4e3a\u5173\u952e\u5b57 let \u4e3a\u6211\u4eec\u63d0\u4f9b\u4e86\u5757\u4f5c\u7528\u57df\u5185\u7684\u53d8\u91cf\uff0c\u8fd9\u610f\u5473\u7740\u5b83\u4eec\u4ec5\u5b58\u5728\u4e8e\u81ea\u5df1\u521b\u5efa\u7684\u4f5c\u7528\u57df\u5185\uff0c\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u4f4d\u4e8eif...else \u8bed\u53e5\u4e2d\u3002\u5185\u90e8\u53d8\u91cf\u4f18\u5148\u4e8e\u5916\u90e8\u53d8\u91cf\uff0c\u8fd9\u5c31\u662f\u4e3a\u4ec0\u4e48\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528\u76f8\u540c\u6807\u8bc6\u7b26\u7684\u539f\u56e0\u3002<\/p>\n
2.\u7ee7\u627f<\/strong><\/span><\/div>\n
\u8003\u8651\u4ee5\u4e0b\u7c7b\uff0c\u5e76\u5c1d\u8bd5\u56de\u7b54\u8f93\u51fa\u4e86\u4ec0\u4e48\u4ee5\u53ca\u4e3a\u4ec0\u4e48\u3002<\/p>\n
class Person { \r\n constructor() { \r\n this.sayHello = () => { \r\n return 'Hello'; \r\n } \r\n } \r\n \r\n sayBye() { \r\n return 'Bye'; \r\n } \r\n} \r\n \r\nclass Student extends Person { \r\n sayHello() { \r\n return 'Hello from Student'; \r\n } \r\n} \r\n \r\nconst student = new Student(); \r\nconsole.log(student.sayHello()); \r\n<\/pre>\n
\u8bf4\u660e
\n\u5982\u679c\u4f60\u7684\u7b54\u6848\u662f Hello\uff0c\u90a3\u662f\u5bf9\u7684!
\n\u4e3a\u4ec0\u4e48\uff1a\u6bcf\u6b21\u6211\u4eec\u521b\u5efa\u4e00\u4e2a\u65b0\u7684 Student \u5b9e\u4f8b\u65f6\uff0c\u90fd\u4f1a\u5c06 sayHello \u5c5e\u6027\u8bbe\u7f6e\u4e3a\u662f\u4e00\u4e2a\u51fd\u6570\uff0c\u5e76\u8fd4\u56de\u5b57\u7b26\u4e32 Hello\u3002\u8fd9\u662f\u5728\u7236\u7c7b(Person)\u7c7b\u7684\u6784\u9020\u51fd\u6570\u4e2d\u53d1\u751f\u7684\u3002
\n\u5728 JavaScript \u4e2d\uff0c\u7c7b\u662f\u8bed\u6cd5\u7cd6\uff0c\u5728\u6211\u4eec\u7684\u4f8b\u5b50\u4e2d\uff0c\u5728\u539f\u578b\u94fe\u4e0a\u5b9a\u4e49\u4e86 Student \u7c7b\u4e2d\u7684 sayHello \u65b9\u6cd5\u3002\u8003\u8651\u5230\u6bcf\u6b21\u6211\u4eec\u521b\u5efa Student \u7c7b\u7684\u5b9e\u4f8b\u65f6\uff0c\u90fd\u4f1a\u5c06 sayHello \u5c5e\u6027\u8bbe\u7f6e\u4e3a\u8be5\u5b9e\u4f8b\uff0c\u4f7f\u5176\u6210\u4e3a\u8fd4\u56de\u5b57\u7b26\u4e32 Hello \u7684 function\uff0c\u56e0\u6b64\u6211\u4eec\u6c38\u8fdc\u4e0d\u4f1a\u4f7f\u7528\u539f\u578b\u94fe\u4e0a\u5b9a\u4e49\u7684\u51fd\u6570\uff0c\u4e5f\u5c31\u6c38\u8fdc\u4e0d\u4f1a\u770b\u5230\u6d88\u606f Hello from Student \u3002<\/p>\n
3.\u5bf9\u8c61\u53ef\u53d8\u6027<\/strong><\/span><\/div>\n
\u601d\u8003\u4ee5\u4e0b\u60c5\u51b5\u4e2d\u6bcf\u4e2a\u90e8\u5206\u7684\u8f93\u51fa\uff1a<\/p>\n
\/\/ situation 1 \r\nconst user = { \r\n name: 'John', \r\n surname: 'Doe' \r\n} \r\n \r\nuser = { \r\n name: 'Mike' \r\n} \r\n \r\nconsole.log(user); \r\n \r\n\/\/ situation 2 \r\nconst user = { \r\n name: 'John', \r\n surname: 'Doe' \r\n} \r\n \r\nuser.name = 'Mike'; \r\nconsole.log(user.name); \r\n \r\n\/\/ situation 3 \r\nconst user = { \r\n name: 'John', \r\n surname: 'Doe' \r\n} \r\n \r\nconst anotherUser = user; \r\nanotherUser.name = 'Mike'; \r\nconsole.log(user.name); \r\n \r\n\/\/ situation 4 \r\nconst user = { \r\n name: 'John', \r\n surname: 'Doe', \r\n address: { \r\n street: 'My Street' \r\n } \r\n} \r\n \r\nObject.freeze(user); \r\n \r\nuser.name = 'Mike'; \r\nuser.address.street = 'My Different Street'; \r\nconsole.log(user.name); \r\nconsole.log(user.address.street); \r\n<\/pre>\n
\u8bf4\u660e
\nSituation 1: \u6b63\u5982\u6211\u4eec\u5728\u4e0a\u4e00\u8282\u4e2d\u6240\u4e86\u89e3\u7684\uff0c\u6211\u4eec\u8bd5\u56fe\u91cd\u65b0\u5206\u914d\u4e0d\u5141\u8bb8\u4f7f\u7528\u7684 const \u53d8\u91cf\uff0c\u6240\u4ee5\u5c06\u4f1a\u5f97\u5230\u7c7b\u578b\u9519\u8bef\u3002
\n\u63a7\u5236\u53f0\u4e2d\u7684\u7ed3\u679c\u5c06\u663e\u793a\u4ee5\u4e0b\u6587\u672c\uff1a<\/p>\n
Uncaught TypeError: Assignment to constant variable \r\n<\/pre>\n
Situation 2: \u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u5373\u4f7f\u6211\u4eec\u6539\u7528\u5173\u952e\u5b57 const \u58f0\u660e\u7684\u53d8\u91cf\uff0c\u4e5f\u4f1a\u6709\u4e0d\u540c\u7684\u884c\u4e3a\u3002\u4e0d\u540c\u4e4b\u5904\u5728\u4e8e\u6211\u4eec\u6b63\u5728\u4fee\u6539\u5bf9\u8c61\u5c5e\u6027\u800c\u4e0d\u662f\u5176\u5f15\u7528\uff0c\u8fd9\u5728 const \u5bf9\u8c61\u53d8\u91cf\u4e2d\u662f\u5141\u8bb8\u7684\u3002
\n\u63a7\u5236\u53f0\u4e2d\u7684\u7ed3\u679c\u5e94\u4e3a\u5355\u8bcd Mike\u3002
\nSituation 3: \u901a\u8fc7\u5c06 user \u5206\u914d\u7ed9 anotherUser \u53d8\u91cf\uff0c\u53ef\u4ee5\u5728\u5b83\u4eec\u4e4b\u95f4\u5171\u4eab\u5f15\u7528\u6216\u5b58\u50a8\u4f4d\u7f6e(\u5982\u679c\u4f60\u613f\u610f)\u3002\u6362\u53e5\u8bdd\u8bf4\uff0c\u5b83\u4eec\u4e24\u4e2a\u90fd\u4f1a\u6307\u5411\u5185\u5b58\u4e2d\u7684\u540c\u4e00\u4e2a\u5bf9\u8c61\uff0c\u56e0\u6240\u4ee5\u66f4\u6539\u4e00\u4e2a\u5bf9\u8c61\u7684\u5c5e\u6027\u5c06\u53cd\u6620\u53e6\u4e00\u4e2a\u5bf9\u8c61\u7684\u66f4\u6539\u3002
\n\u63a7\u5236\u53f0\u4e2d\u7684\u7ed3\u679c\u5e94\u4e3a Mike\u3002
\nSituation 4: \u5728\u8fd9\u91cc\uff0c\u6211\u4eec\u4f7f\u7528 Object.freeze \u65b9\u6cd5\u6765\u63d0\u4f9b\u5148\u524d\u573a\u666f(Situation 3)\u6240\u7f3a\u4e4f\u7684\u529f\u80fd\u3002\u901a\u8fc7\u8fd9\u4e2a\u65b9\u6cd5\uff0c\u6211\u4eec\u53ef\u4ee5\u201c\u51bb\u7ed3\u201d\u5bf9\u8c61\uff0c\u4ece\u800c\u4e0d\u5141\u8bb8\u4fee\u6539\u5b83\u7684\u5c5e\u6027\u503c\u3002\u4f46\u662f\u6709\u4e00\u4e2a\u95ee\u9898!\u5b83\u53ea\u4f1a\u8fdb\u884c\u6d45\u51bb\u7ed3\uff0c\u8fd9\u610f\u5473\u7740\u5b83\u4e0d\u4f1a\u4fdd\u62a4\u6df1\u5c42\u5c5e\u6027\u7684\u66f4\u65b0\u3002\u8fd9\u5c31\u662f\u4e3a\u4ec0\u4e48\u6211\u4eec\u80fd\u591f\u5bf9 street \u5c5e\u6027\u8fdb\u884c\u66f4\u6539\uff0c\u800c name \u5c5e\u6027\u4fdd\u6301\u4e0d\u53d8\u7684\u539f\u56e0\u3002
\n\u63a7\u5236\u53f0\u4e2d\u7684\u8f93\u51fa\u4f9d\u6b21\u4e3a John \u548c My Different Street \u3002<\/p>\n
4.\u7bad\u5934\u51fd\u6570<\/strong><\/span><\/div>\n
\u8fd0\u884c\u4ee5\u4e0b\u4ee3\u7801\u6bb5\u540e\uff0c\u5c06\u4f1a\u8f93\u51fa\u4ec0\u4e48\u4ee5\u53ca\u539f\u56e0\uff1a<\/p>\n
const student = { \r\n school: 'My School', \r\n fullName: 'John Doe', \r\n printName: () => { \r\n console.log(this.fullName); \r\n }, \r\n printSchool: function () { \r\n console.log(this.school); \r\n } \r\n}; \r\n \r\nstudent.printName(); \r\nstudent.printSchool(); \r\n<\/pre>\n
\u8bf4\u660e
\n\u63a7\u5236\u53f0\u4e2d\u7684\u8f93\u51fa\u5c06\u4f9d\u6b21\u4e3a undefined \u548c My School\u3002
\n\u4f60\u53ef\u80fd\u4f1a\u719f\u6089\u4ee5\u4e0b\u8bed\u6cd5\uff1a<\/p>\n
var me = this; \r\n\/\/ or \r\nvar self = this; \r\n \r\n\/\/ ... \r\n\/\/ ... \r\n\/\/ somewhere deep... \r\n\/\/ me.doSomething(); \r\n<\/pre>\n
\u4f60\u53ef\u4ee5\u628a me \u6216 self \u53d8\u91cf\u89c6\u4e3a\u7236\u4f5c\u7528\u57df\uff0c\u8be5\u4f5c\u7528\u57df\u53ef\u7528\u4e8e\u5728\u5176\u4e2d\u521b\u5efa\u7684\u6bcf\u4e2a\u5d4c\u5957\u51fd\u6570\u3002
\n\u5f53\u4f7f\u7528\u7bad\u5934\u51fd\u6570\u65f6\uff0c\u8fd9\u4f1a\u81ea\u52a8\u5b8c\u6210\uff0c\u6211\u4eec\u4e0d\u518d\u9700\u8981\u5b58\u50a8 this \u5f15\u7528\u6765\u8bbf\u95ee\u4ee3\u7801\u4e2d\u66f4\u6df1\u7684\u5730\u65b9\u3002\u7bad\u5934\u51fd\u6570\u4e0d\u7ed1\u5b9a\u81ea\u5df1\uff0c\u800c\u662f\u4ece\u7236\u4f5c\u7528\u57df\u7ee7\u627f\u4e00\u4e2a\u7bad\u5934\u51fd\u6570\uff0c\u8fd9\u5c31\u662f\u4e3a\u4ec0\u4e48\u5728\u8c03\u7528 printName \u51fd\u6570\u540e\u8f93\u51fa\u4e86 undefined \u7684\u539f\u56e0\u3002<\/p>\n
5.\u89e3\u6784<\/strong><\/span><\/div>\n
\u8bf7\u67e5\u770b\u4e0b\u9762\u7684\u9500\u6bc1\u4fe1\u606f\uff0c\u5e76\u56de\u7b54\u5c06\u8981\u8f93\u51fa\u7684\u5185\u5bb9\u3002\u7ed9\u5b9a\u7684\u8bed\u6cd5\u662f\u5426\u5141\u8bb8\uff0c\u5426\u5219\u4f1a\u5f15\u53d1\u9519\u8bef?<\/p>\n
const rawUser = { \r\n name: 'John', \r\n surname: 'Doe', \r\n email: 'john@doe.com', \r\n displayName: 'SuperCoolJohn', \r\n joined: '2016-05-05', \r\n image: 'path-to-the-image', \r\n followers: 45 \r\n} \r\n \r\nlet user = {}, userDetails = {}; \r\n({ name: user.name, surname: user.surname, ...userDetails } = rawUser); \r\n \r\nconsole.log(user); \r\nconsole.log(userDetails);\r\n<\/pre>\n
\u8bf4\u660e
\n\u5c3d\u7ba1\u6709\u70b9\u5f00\u7bb1\u5373\u7528\uff0c\u4f46\u662f\u4e0a\u9762\u7684\u8bed\u6cd5\u662f\u5141\u8bb8\u7684\uff0c\u5e76\u4e14\u4e0d\u4f1a\u5f15\u53d1\u9519\u8bef! \u5f88\u6574\u6d01\u5427?
\n\u4e0a\u9762\u7684\u8bed\u6cd5\u529f\u80fd\u5f3a\u5927\uff0c\u4f7f\u6211\u4eec\u80fd\u591f\u8f7b\u677e\u5730\u5c06\u4efb\u4f55\u5bf9\u8c61\u5206\u6210\u4e24\u4e2a\u66f4\u5177\u4f53\u7684\u5bf9\u8c61\uff0c\u4e0a\u9762\u7684\u793a\u4f8b\u5728\u63a7\u5236\u53f0\u7684\u8f93\u51fa\u4e3a\uff1a<\/p>\n
\/\/ {name: \"John\", surname: \"Doe\"} \r\n\/\/ {email: \"john@doe.com\", displayName: \"SuperCoolJohn\", joined: \"2016-05-05\", image: \"path-to-the-image\", followers: 45} \r\n<\/pre>\n
6.\u5f02\u6b65\/\u7b49\u5f85<\/strong><\/span><\/div>\n
\u8c03\u7528\u4ee5\u4e0b\u51fd\u6570\u540e\u5c06\u8f93\u51fa\u4ec0\u4e48?<\/p>\n
(async () => { \r\n let result = 'Some Data'; \r\n \r\n let promise = new Promise((resolve, reject) => { \r\n setTimeout(() => resolve('Some data retrieved from the server'), 2000); \r\n }); \r\n \r\n result = await promise; \r\n console.log(result); \r\n})(); \r\n<\/pre>\n
\u8bf4\u660e
\n\u5982\u679c\u4f60\u8ba4\u4e3a\u662f\u4e24\u79d2\u949f\u540e\u8f93\u51fa Some data retrieved from the server \uff0c\u90a3\u4e48\u4f60\u662f\u5bf9\u7684!
\n\u4ee3\u7801\u5c06\u4f1a\u6682\u505c\uff0c\u76f4\u5230 promise \u5f97\u5230\u89e3\u51b3\u3002\u4e24\u79d2\u949f\u540e\uff0c\u5b83\u5c06\u7ee7\u7eed\u6267\u884c\u5e76\u8f93\u51fa\u7ed9\u5b9a\u7684\u6587\u672c\u3002\u8fd9\u610f\u5473\u7740 JavaScript \u5f15\u64ce\u5b9e\u9645\u4e0a\u4f1a\u7b49\u5230\u5f02\u6b65\u64cd\u4f5c\u5b8c\u6210\u3002\u53ef\u4ee5\u8bf4 async\/await \u662f\u7528\u6765\u83b7\u5f97 promise \u7ed3\u679c\u7684\u8bed\u6cd5\u7cd6\u3002\u4e5f\u6709\u4eba\u8ba4\u4e3a\u5b83\u662f\u6bd4 promise.then \u66f4\u5177\u53ef\u8bfb\u6027\u7684\u65b9\u5f0f\u3002<\/p>\n
7. Return \u8bed\u53e5<\/strong><\/span><\/div>\n
const multiplyByTwo = (x) => { \r\n return \r\n { \r\n result: x * 2 \r\n }; \r\n} \r\nconsole.log(multiplyByTwo(2)); \r\n<\/pre>\n
\u8bf4\u660e
\n\u5982\u679c\u4f60\u7684\u7b54\u6848\u662f {result: 4}\uff0c\u90a3\u4f60\u5c31\u9519\u4e86\u3002\u8f93\u51fa\u662f undefined\u3002\u4f46\u662f\u4e0d\u8981\u5bf9\u81ea\u5df1\u592a\u82db\u523b\uff0c\u8003\u8651\u5230\u6211\u4e5f\u5199 C# \u4ee3\u7801\uff0c\u8fd9\u4e5f\u66fe\u7ecf\u56f0\u6270\u7740\u6211\uff0c\u8fd9\u5728 C# \u90a3\u513f\u4e0d\u662f\u4e2a\u95ee\u9898\u3002
\n\u7531\u4e8e\u81ea\u52a8\u5206\u53f7\u63d2\u5165\u7684\u539f\u56e0\uff0c\u4e0a\u9762\u7684\u4ee3\u7801\u5c06\u8fd4\u56de undefined\u3002 return \u5173\u952e\u5b57\u548c\u8868\u8fbe\u5f0f\u4e4b\u95f4\u4e0d\u5141\u8bb8\u4f7f\u7528\u884c\u7ed3\u675f\u7b26
\n\u89e3\u51b3\u65b9\u6848\u662f\u7528\u4ee5\u4e0b\u5217\u65b9\u5f0f\u4e4b\u4e00\u53bb\u4fee\u590d\u8fd9\u4e2a\u51fd\u6570\uff1a<\/p>\n
const multiplyByTwo = (x) => { \r\n return { \r\n result: x * 2 \r\n }; \r\n} \r\n\u8981\u4e48\r\n\r\nconst multiplyByTwo = (x) => { \r\n return ( \r\n { \r\n result: x * 2 \r\n } \r\n ); \r\n} \r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
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