Merge pull request #469 from Girlwithasmile/type

Created typescript.md

typescript.md

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+---
+title: Typescript
+description: tells about basic functions, variables and operations in typescript.
+created: 2022-10-20
+---
+<br>
+
+Basic hello world program<br>
+```typescript
+console.log(‘Hello World’);
+```
+Basic types in typescript and values compiler assumes<br>
+Untyped => &nbsp; any<br>
+A string => &nbsp; string<br>
+A true/false value => &nbsp; boolean<br>
+Explicitly empty value => &nbsp; null<br>
+Uninitialised value => &nbsp; undefined
+
+Declaring/ Using variables in typescript
+```typescript
+let age :  number = 10;
+if (age < 50)
+   age += 5;
+console.log(age);
+```
+Literal types<br>
+In Strings
+```typescript
+let hand: 'left' | 'right';
+```
+In Numeric
+```typescript
+let dice roll: 1 | 2 | 3 | 4 | 5 | 6;
+```
+
+Built-in types<br>
+```typescript
+let students: number = 123_456_321;
+let course: string = ‘Typescript’;
+let course : boolean = true;
+```
+Typescript can also define types on their own.
+```typescript
+let fruits = 4;
+let medium = ‘English’;
+```
+Here, compiler understands and hence allots the type numeric to 4, and string to English.
+<br><br>
+Arrays in typescript
+```typescript
+let numbers = [1, 2, 3];
+```
+Array is used to store elements of same type.
+Empty array is given by
+```typescript
+let numbers: number[]  = [];
+```
+Tuple in typescript
+```typescript
+let user: [number, string] = [1, ‘Surabhi’];
+```
+Tuples are greatly useful when we want to store two types of values like numeric-string, string-boolean,etc.
+
+Typescript has a data type named Enum.
+```typescript
+enum Size { Small, Medium, Large};
+//In this scenario compiler has assumed small to be 0.
+//If we explicitly want to set values then
+enum Size { Small = 1, Medium, Large}
+enum Size { Small = ‘s’, Medium = ‘m’, Large= ‘l’ };
+```
+Pascal Code
+```typescript
+enum Size {Small=1, Medium, Large};
+let mySize: Size = Size.Medium;
+console.log(mySize);
+```
+
+<b>Functions</b>
+```typescript  
+  function calculateTax(income:number) : number{
+if (income > 1000)
+    return income * 1.2
+return income*2
+}
+ ```
+Constructors
+```
+new () => ConstructedType;
+```
+
+Functions with optional parameter
+```typescript
+function calculateTax(income: number, taxYear:number): number {
+      if (taxYear < 2022)
+          return income*2.2
+return income*1.5
+}
+calculateTax( 2000, 2022);
+```
+We can perform operations like union and intersection in typescript.
+Union
+```typescript
+function kgtolbs(weight: number | string) : number
+```
+Intersection
+```typescript
+let myIntersection : Engineering & Coding;
+```
+Utility types
+```typescript
+Record<'x' | 'y' | 'z', number>
+```
+is equivalent to
+```typescript
+{ x: number; y: number; z: number; }
+```
+Similarly
+```typescript
+type Excluded = Exclude<string | number, string>;
+```
+is equivalent to
+```typescript
+number
+```
+Similarly,
+```typescript
+type Extracted = Extract<string | number, string>;
+```
+is equivalent to
+```typescript
+string
+```