# TypeScript 基礎知識

###### tags: `TypeScript`

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~~*ps.作為自己學習筆記之用，如有錯漏請高抬貴手QQ*~~

## 一般變數宣告
TypeScript的變數皆於一開始就宣告變數型別，可避免JavaScript變數型別轉換可能的錯誤，對於之後程式維護與Debug可說是非常有幫助。

* 有幾種變數宣告型別
* <span class="code1">var</span>
* <span class="code1">let</span>
* <span class="code1">const</span>
* <span class="code2">Tuple</span>

變數的宣告方式:

var abc:string = "Hello";    //宣告為字串

var num:number = 12;    //宣告為數字

var apple:any = 10;   //可存放任意型別的值

let bca:string;

const sum = 50;        //設定常數型別

let ayy:number[]= [1,2,3,4,5];

也可以自訂變數名稱，並設定對應的型別:(好處是之後查找型別非常方便)

type phone = number;  //使用let a:phone; 取用變數
type email = string;    //使用let b:email; 取用變數

type ayy = string[];

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## 列舉型別(enum)
特色為只能預先存入固定數量的內容值的型別，建立後無法再存入其他的值。

enum Season { spring, summer, autumn, winter };

let s: Season = Season.summer;  //取用enum Season的值

switch (s) {
    case Season.spring:
        document.write('<h1>Spring</h1>');
        break;
    case Season.summer:
        document.write('<h1>Summer</h1>');
        break;
    case Season.autumn:
        document.write('<h1>Autumn</h1>');
        break;
    case Season.winter:
        document.write('<h1>Winter</h1>');
        break;
}
document.write('<p>顯示目前的季節:</p>');

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## Tuple 型別變數

type name = string;
type phone = number;
type email = string;

let person[name, phone, email];

person['Peter', 0900123456, '[e-mail]'];
person['Ella', 0900123466, '[e-mail]'];

document.write(person);

---
<span class="code1"></span>
<style>
h2 {
color: #2383B8;
}
h3 {
color: #1AA340;
}
h4 {
color: white;
background-color: #2383B8;
padding:8px;
}

.code1 {
padding: 2px 4px;
font-size: 90%;
color: #c7254e;
background-color: #f9f2f4;
border-radius: 4px;
font-family:'Fira Code';
}
.code {
padding: 2px 4px;
font-size: 90%;
font-family:'Fira Code';
}
</style>