TypeScript基礎之基本類型檢查

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})\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"null和undefined","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"null","attrs":{}}],"attrs":{}},{"type":"text","text":"和","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"undefined","attrs":{}}],"attrs":{}},{"type":"text","text":"需要重點說一下，","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"null","attrs":{}}],"attrs":{}},{"type":"text","text":"和","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"undefined","attrs":{}}],"attrs":{}},{"type":"text","text":"是所有其他類型的子類型，它們可以賦值給其它類型，但是又會發生隱患，下面方法調用都會報錯，由於約束了是","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"string","attrs":{}}],"attrs":{}},{"type":"text","text":"和","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"number","attrs":{}}],"attrs":{}},{"type":"text","text":"，但是值又是","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"null","attrs":{}}],"attrs":{}},{"type":"text","text":"和","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"undefined","attrs":{}}],"attrs":{}},{"type":"text","text":"，這種情況是我們不希望發生的。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":" let str:string = null;\n let nums:number = undefined;\n \n //下面都會報錯，由於約束了是string和number，但是值又是null和undefined\n str.toLocaleUpperCase();\n nums.toString();\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"👉 ","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"解決方案：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"在`tsconfi.json`配置文件中加上：`\"strictNullChecks\": true`之後可以獲得更加嚴格的空類型檢查，`null`和`undefined`就不能賦值給其它的了\n\n\n","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"3. 其它常用類型","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"聯合類型：多種類型任選其一","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"當一個變量既可以爲","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"字符串","attrs":{}}],"attrs":{}},{"type":"text","text":"又可以爲","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"undefined","attrs":{}}],"attrs":{}},{"type":"text","text":"的時候就可以使用","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"聯合類型","attrs":{}}],"attrs":{}},{"type":"text","text":"，它可以配合使用","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"類型保護","attrs":{}}],"attrs":{}},{"type":"text","text":"進行判斷","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":"none"},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"📢 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"類型保護：","attrs":{}}],"attrs":{}},{"type":"text","text":"當對某個變量進行類型判斷之後，在判斷的語句中便可以確定它的確切類型，typeof也","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"可以觸發類型保護，但是它只能觸發簡單基本的類型保護，複雜類型是沒有辦法觸發的","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":" let user:string | undefined;\n\n if(typeof user === \"string\"){\n //類型保護，當進入這個判斷，TS一定會知道，此時user一定是字符串\n }\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"void類型：通常用於約束函數返回值，表示該函數沒有任何io","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"void","attrs":{}}],"attrs":{}},{"type":"text","text":"在","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Js","attrs":{}}],"attrs":{}},{"type":"text","text":"也是有的，表示運算一個表達式之後返回undefined，但在","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"TS","attrs":{}}],"attrs":{}},{"type":"text","text":"意思是不同的，通常用於約束函數返回值，表示該函數沒有任何返回","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":" function user():void{\n console.log(\"法醫\");\n }\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"當然不約束也是可以的，因爲會`類型推導`出來\n\n\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"never類型：通常用於約束函數返回值，表示該函數永遠不可能結束","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":" function thorwError(msg:string) {\n throw new Error(msg)\n }\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"這個函數的`類型推導`是有問題的，推導的類型是`viod`，因爲它永遠不會結束，類型應該是`never`而不是`viod`，所以需要手動更改\n\n\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":" function thorwError(msg:string):never {\n throw new Error(msg)\n }\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"由於是永遠不會結束，所以，下面的log函數無法執行，無法訪問代碼\n\n\n\n還有一種情況也是永遠不會結束，需要手動約束\n\n\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"字面量類型：使用一個","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"值","attrs":{}}],"attrs":{}},{"type":"text","text":"進行約束，而不是","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"類型","attrs":{}}],"attrs":{}},{"type":"text","text":"約束","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":" //表示從此以後，變量name只能是 “法醫”，別的就會報錯\n let name:\"法醫\";\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"\n\n一般我們可以用字面量類型對性別或者對象中的屬性進行約束：\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":" //對gender 變量進行約束，只能是男或女，其它不行\n let gender :\"男\" | \"女\";\n \n //對users對象中的name和age屬性分別約束爲字符串和數字，下次給users賦值的時候，只能包含name和age\n let users:{\n name:string\n age:number\n }\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"元組類型(Tuple)：用的不多，瞭解一下就可以了，表示固定長度的數組，並且數組中的每一項類型確定","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":" //定義了一個變量爲tupleType的數組，這個數組只能有兩項，並且第一個必須爲字符串，第二個必須爲數字\n let tupleType:[string,number];\n \n //第一項必須爲字符串，第二項必須爲數字，只能有兩項，否則報錯\n tupleType = [\"法醫\",5];\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"any類型：any類型可以繞過類型檢查，因此any類型可以賦值給任意類型，但肯定是有隱患的，因爲它無法使用TS提供的保護機制，所以不建議隨意的使用","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"any","attrs":{}}],"attrs":{}},{"type":"text","text":"類型，爲了解決any帶來的問題，","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"TS3.0","attrs":{}}],"attrs":{}},{"type":"text","text":"引入了","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"unknown","attrs":{}}],"attrs":{}},{"type":"text","text":"類型","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d1/d173b23e441c895ae2b51b19d407e74b.gif","alt":null,"title":"","style":[{"key":"width","value":"100%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"4. 類型別名","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"給已知的類型起個新的名字，防止重複書寫一些代碼","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"type Gender = \"男\" | \"女\";\ntype user = {\n name:string\n age:number\n gender:Gender\n}\n\nfunction getUser(g:Gender) {\n //...\n}\n","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"5. 函數的相關約束","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"函數重載","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"先看一個函數","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"combine","attrs":{}}],"attrs":{}},{"type":"text","text":"，功能是如果傳遞兩個數字作爲參數的時候相乘，傳遞兩個字符串的時候相加，不相同都會報錯。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"function combine(a:number | string,b:number | string):number | string {\n if(typeof a === \"number\" && typeof b === \"number\"){\n return a * b;\n }\n else if(typeof a === \"string\" && typeof b === \"string\"){\n return a + b;\n }\n throw new Error(\"a和b必須是相同的類型\")\n}\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"函數本身沒有什麼問題，問題就發生在函數調用的過程中，當我們代碼寫多了以後，我們也許會失誤傳遞不同的類型作爲參數，更可怕的是如果參數是函數的返回結果，那就更蒙了，因此，在函數的調用過程中最好告訴調用函數，要麼都是數字類型，要麼都是字符串類型。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/22/22628bcb51ec34ef3f2efffa0384b389.gif","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"從邏輯上來說，都是數字的話返回的結果就是數字類型，都是字符串的話返回的結果就是字符串類型，然而","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"result","attrs":{}}],"attrs":{}},{"type":"text","text":"的類型是","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"string | 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","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"解決方案：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"加上下面兩句代碼，這兩句代碼相當於告訴 TS ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"combine函數","attrs":{}}],"attrs":{}},{"type":"text","text":"只能有兩種情況，一種是兩個數字返回數字，另一種是兩個字符串返回字符串，這兩句代碼就叫","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"函數重載","attrs":{}}],"attrs":{}},{"type":"text","text":"。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"📢 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"函數重載：","attrs":{}}],"attrs":{}},{"type":"text","text":"在函數實現之前，對函數調用的多種情況進行聲明。","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"//加上這兩句代碼\n/**\n * 得到a * b的結果\n * @param a \n * @param b \n */\nfunction combine(a:number,b:number):number;\n/**\n * 得到a + b的結果\n * @param a \n * @param b \n */\nfunction combine(a:string,b:string):string;\n\nfunction combine(a:number | string,b:number | string):number | string {\n if(typeof a === \"number\" && typeof b === \"number\"){\n return a * b;\n }\n else if(typeof a === \"string\" && typeof b === \"string\"){\n return a + b;\n }\n throw new Error(\"a和b必須是相同的類型\")\n}\n\nlet result = combine(\"b\",\"n\");\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"使用函數重載之後，當調用函數的時候只能傳兩個數字或者兩個字符串，否則會報錯，再來看看效果：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/95/95d5bc572e109500d8799f691b4be239.gif","alt":null,"title":"","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"可選參數","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"📢 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"可選參數：","attrs":{}}],"attrs":{}},{"type":"text","text":"可以在某些參數名後面加上","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"？","attrs":{}}],"attrs":{}},{"type":"text","text":"號，表示該參數可以不用傳遞。可選參數必須要在參數列表的末尾","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/5b/5b1df837cf9b2b87492b67370a9d89f5.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"當形參爲三個，調用函數卻傳了兩個，就會報錯，TS是很嚴格的，不允許參數數量不匹配。假設第三個參數可以不傳遞，加個","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"？","attrs":{}}],"attrs":{}},{"type":"text","text":"號表示是可選參數","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/67/67f437608917cdebc07de326064d667e.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"😛 結束語","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"寫完又是深夜了，TS的基礎之基本類型檢查就寫完了，本來想着把TS基礎部分整理成","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"萬字文","attrs":{}}],"attrs":{}},{"type":"text","text":"再分享給大家的，但又覺得篇幅過長閱讀不便，那就慢慢更新吧，9月份不出意外的話基本上每天會更新一篇，有任何疑問可以留言，小夥伴們點個贊 👍 關注➕再走吧！～ 😘，我會更有動力的，晚安！ 🤞","attrs":{}}]}]}