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TypeScript programs consist of the following parts: * Modules * Functions * Variables * Statements and expressions * Comments ### The First TypeScript Program We can use the following TypeScript program to output "Hello World": ## Tutorial.ts file code: const hello : string = "Hello World!"console.log(hello) [Try it »](#) The above code is first compiled using the **tsc** command: tsc Tutorial.ts We get the following js code: ## Tutorial.js file code: var hello = "Hello World!"; console.log(hello); Finally we use the node command to execute this js code. $ node Tutorial.js Hello World The entire process is shown in the figure below: !(#) We can compile multiple ts files at the same time: tsc file1.ts file2.ts file3.ts Common tsc compilation parameters are shown in the table below: | No. | Compilation Parameter Description | | --- | --- | | 1. | **--help** Display help information | | 2. | **--module** Load extension module | | 3. | **--target** Set ECMA version | | 4. | **--declaration** Additionally generate a .d.ts extension file. tsc ts-hw.ts --declaration The above command will generate ts-hw.d.ts and ts-hw.js two files. | | 5. | **--removeComments** Remove comments from the file | | 6. | **--out** Compile multiple files and merge into one output file | | 7. | **--sourcemap** Generate a sourcemap (.map) file. sourcemap is an information file that stores the mapping between source code and compiled code positions. | | 8. | **--module noImplicitAny** Report error when there is implicit any type in expressions and declarations | | 9. | **--watch** Run the compiler in watch mode. It will watch output files and recompile them when they change. | * * * ## TypeScript Reserved Keywords TypeScript reserved keywords are shown in the table below: | Keyword | Description | | --- | --- | | `abstract` | Used to define abstract classes or abstract methods. | | `any` | Represents any type, disables type checking. | | `as` | Type assertion, used to convert one type to another. | | `await` | Used in async functions to pause code execution until the Promise resolves. | | `boolean` | Represents boolean type. | | `break` | Exit loop or switch statement. | | `case` | Used for branches in switch statements. | | `catch` | Used to catch exceptions. | | `class` | Used to define a class. | | `const` | Define constant variables. | | `continue` | Skip current loop and continue to next iteration. | | `debugger` | Start debugger and pause code execution. | | `declare` | Declare a variable or module, usually used in type declaration files. | | `default` | Define default branch in switch statement. | | `delete` | Delete property of object or element of array. | | `do` | Used in `do...while` loop. | | `else` | Define else part in conditional statement. | | `enum` | Define enumeration type. | | `export` | Used to export variables, functions or classes from a module. | | `extends` | Used for class inheritance, indicates that a class inherits from another class. | | `false` | Boolean value `false`. | | `finally` | Define the finally execution block in `try...catch` statement. | | `for` | Used in `for` loop. | | `from` | Used in module import statements to specify the source of the module. | | `function` | Define a function. | | `get` | Used for getter method of an object. | | `if` | Used for conditional judgment. | | `implements` | Used for a class to implement an interface. | | `import` | Used to import content from a module. | | `in` | Used to check if an object contains a specified property, or used in `for...in` loop. | | `infer` | Used in conditional types to infer types. | | `instanceof` | Check if an object is an instance of a specified class. | | `interface` | Used to define an interface. | | `let` | Define block-scoped variables. | | `module` | Define a module (used in earlier TypeScript versions). | | `namespace` | Define a namespace (used in earlier TypeScript versions). | | `new` | Create an instance of a class. | | `null` | Represents null value. | | `number` | Represents number type. | | `object` | Represents non-primitive type. | | `of` | Used in `for...of` loop. | | `package` | Used in module system to identify a package. | | `private` | Used as access modifier for class members, indicates private. | | `protected` | Used as access modifier for class members, indicates protected. | | `public` | Used as access modifier for class members, indicates public. | | `readonly` | Represents read-only property. | | `require` | Used to import CommonJS modules. | | `return` | Exit function and can return a value. | | `set` | Used for setter method of an object. | | `string` | Represents string type. | | `super` | Used to call parent class's method or constructor. | | `switch` | Used in switch statement. | | `symbol` | Represents symbol type. | | `this` | Reference to current class or object's instance. | | `throw` | Throw an exception. | | `try` | Used in exception handling statement `try...catch`. | | `true` | Boolean value `true`. | | `type` | Used to define type aliases. | | `typeof` | Get the type of a variable or expression. | | `undefined` | Represents undefined value. | | `