怎么使用TypeScript？

本地环境搭建（使用vscode）

1、初始化项目，新建package.json

• 创建项目文件夹 mkdir test
• 使用npm初始化项目 npm init

2、安装typescript

• npm install typescript -D

3、将typescript编译成JavaScript

• npx tsc 文件名

什么是ts TypeScript?

eg1:type Result = 'a' | 'b'function test(result: Result) {if (result === 'a'){console.log('a')} else {console.log('b')}
//使用 npx tsc test1.ts => test1.jsfunction test(result) {if (result === 'a'){console.log('a')} else {console.log('b')}eg2:const hello = name => {console.log(`h,${name}`) //es6字符串模板语法}hello('abc')
//使用 npx tsc test2.ts => test2.jsvar hello = function(name) {console.log("h,".concat(name)) // es3  concat api 进行拼接}hello('abc')eg3:const hello = (name:string)=> {console.log(`h,${name}`) //es6字符串模板语法}hello(66) // 报错 类型 number 的参数不能赋给类型 string 的参数。
//使用 npx tsc test3.ts => test3.jsvar hello = function(name) {console.log("h,".concat(name)) // es3  concat api 进行拼接}hello(66)

4、新建一个tsconfig.json

• npx tsc --init

下面是tsconfig.json文件里的参数

target：编译代码后的兼容参数

...

{"compilerOptions": {/* Visit https://aka.ms/tsconfig to read more about this file *//* Projects */// "incremental": true,                              /* Save .tsbuildinfo files to allow for incremental compilation of projects. */// "composite": true,                                /* Enable constraints that allow a TypeScript project to be used with project references. */// "tsBuildInfoFile": "./.tsbuildinfo",              /* Specify the path to .tsbuildinfo incremental compilation file. */// "disableSourceOfProjectReferenceRedirect": true,  /* Disable preferring source files instead of declaration files when referencing composite projects. */// "disableSolutionSearching": true,                 /* Opt a project out of multi-project reference checking when editing. */// "disableReferencedProjectLoad": true,             /* Reduce the number of projects loaded automatically by TypeScript. *//* Language and Environment */"target": "es2016",                                  /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */// "lib": [],                                        /* Specify a set of bundled library declaration files that describe the target runtime environment. */// "jsx": "preserve",                                /* Specify what JSX code is generated. */// "experimentalDecorators": true,                   /* Enable experimental support for legacy experimental decorators. */// "emitDecoratorMetadata": true,                    /* Emit design-type metadata for decorated declarations in source files. */// "jsxFactory": "",                                 /* Specify the JSX factory function used when targeting React JSX emit, e.g. 'React.createElement' or 'h'. */// "jsxFragmentFactory": "",                         /* Specify the JSX Fragment reference used for fragments when targeting React JSX emit e.g. 'React.Fragment' or 'Fragment'. */// "jsxImportSource": "",                            /* Specify module specifier used to import the JSX factory functions when using 'jsx: react-jsx*'. */// "reactNamespace": "",                             /* Specify the object invoked for 'createElement'. This only applies when targeting 'react' JSX emit. */// "noLib": true,                                    /* Disable including any library files, including the default lib.d.ts. */// "useDefineForClassFields": true,                  /* Emit ECMAScript-standard-compliant class fields. */// "moduleDetection": "auto",                        /* Control what method is used to detect module-format JS files. *//* Modules */"module": "commonjs",                                /* Specify what module code is generated. */// "rootDir": "./",                                  /* Specify the root folder within your source files. */// "moduleResolution": "node10",                     /* Specify how TypeScript looks up a file from a given module specifier. */// "baseUrl": "./",                                  /* Specify the base directory to resolve non-relative module names. */// "paths": {},                                      /* Specify a set of entries that re-map imports to additional lookup locations. */// "rootDirs": [],                                   /* Allow multiple folders to be treated as one when resolving modules. */// "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */// "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */// "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */// "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */// "allowImportingTsExtensions": true,               /* Allow imports to include TypeScript file extensions. Requires '--moduleResolution bundler' and either '--noEmit' or '--emitDeclarationOnly' to be set. */// "resolvePackageJsonExports": true,                /* Use the package.json 'exports' field when resolving package imports. */// "resolvePackageJsonImports": true,                /* Use the package.json 'imports' field when resolving imports. */// "customConditions": [],                           /* Conditions to set in addition to the resolver-specific defaults when resolving imports. */// "resolveJsonModule": true,                        /* Enable importing .json files. */// "allowArbitraryExtensions": true,                 /* Enable importing files with any extension, provided a declaration file is present. */// "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. *//* JavaScript Support */// "allowJs": true,                                  /* Allow JavaScript files to be a part of your program. Use the 'checkJS' option to get errors from these files. */// "checkJs": true,                                  /* Enable error reporting in type-checked JavaScript files. */// "maxNodeModuleJsDepth": 1,                        /* Specify the maximum folder depth used for checking JavaScript files from 'node_modules'. Only applicable with 'allowJs'. *//* Emit */// "declaration": true,                              /* Generate .d.ts files from TypeScript and JavaScript files in your project. */// "declarationMap": true,                           /* Create sourcemaps for d.ts files. */// "emitDeclarationOnly": true,                      /* Only output d.ts files and not JavaScript files. */// "sourceMap": true,                                /* Create source map files for emitted JavaScript files. */// "inlineSourceMap": true,                          /* Include sourcemap files inside the emitted JavaScript. */// "outFile": "./",                                  /* Specify a file that bundles all outputs into one JavaScript file. If 'declaration' is true, also designates a file that bundles all .d.ts output. */// "outDir": "./",                                   /* Specify an output folder for all emitted files. */// "removeComments": true,                           /* Disable emitting comments. */// "noEmit": true,                                   /* Disable emitting files from a compilation. */// "importHelpers": true,                            /* Allow importing helper functions from tslib once per project, instead of including them per-file. */// "importsNotUsedAsValues": "remove",               /* Specify emit/checking behavior for imports that are only used for types. */// "downlevelIteration": true,                       /* Emit more compliant, but verbose and less performant JavaScript for iteration. */// "sourceRoot": "",                                 /* Specify the root path for debuggers to find the reference source code. */// "mapRoot": "",                                    /* Specify the location where debugger should locate map files instead of generated locations. */// "inlineSources": true,                            /* Include source code in the sourcemaps inside the emitted JavaScript. */// "emitBOM": true,                                  /* Emit a UTF-8 Byte Order Mark (BOM) in the beginning of output files. */// "newLine": "crlf",                                /* Set the newline character for emitting files. */// "stripInternal": true,                            /* Disable emitting declarations that have '@internal' in their JSDoc comments. */// "noEmitHelpers": true,                            /* Disable generating custom helper functions like '__extends' in compiled output. */// "noEmitOnError": true,                            /* Disable emitting files if any type checking errors are reported. */// "preserveConstEnums": true,                       /* Disable erasing 'const enum' declarations in generated code. */// "declarationDir": "./",                           /* Specify the output directory for generated declaration files. */// "preserveValueImports": true,                     /* Preserve unused imported values in the JavaScript output that would otherwise be removed. *//* Interop Constraints */// "isolatedModules": true,                          /* Ensure that each file can be safely transpiled without relying on other imports. */// "verbatimModuleSyntax": true,                     /* Do not transform or elide any imports or exports not marked as type-only, ensuring they are written in the output file's format based on the 'module' setting. */// "allowSyntheticDefaultImports": true,             /* Allow 'import x from y' when a module doesn't have a default export. */"esModuleInterop": true,                             /* Emit additional JavaScript to ease support for importing CommonJS modules. This enables 'allowSyntheticDefaultImports' for type compatibility. */// "preserveSymlinks": true,                         /* Disable resolving symlinks to their realpath. This correlates to the same flag in node. */"forceConsistentCasingInFileNames": true,            /* Ensure that casing is correct in imports. *//* Type Checking */"strict": true,                                      /* Enable all strict type-checking options. */// "noImplicitAny": true,                            /* Enable error reporting for expressions and declarations with an implied 'any' type. */// "strictNullChecks": true,                         /* When type checking, take into account 'null' and 'undefined'. */// "strictFunctionTypes": true,                      /* When assigning functions, check to ensure parameters and the return values are subtype-compatible. */// "strictBindCallApply": true,                      /* Check that the arguments for 'bind', 'call', and 'apply' methods match the original function. */// "strictPropertyInitialization": true,             /* Check for class properties that are declared but not set in the constructor. */// "noImplicitThis": true,                           /* Enable error reporting when 'this' is given the type 'any'. */// "useUnknownInCatchVariables": true,               /* Default catch clause variables as 'unknown' instead of 'any'. */// "alwaysStrict": true,                             /* Ensure 'use strict' is always emitted. */// "noUnusedLocals": true,                           /* Enable error reporting when local variables aren't read. */// "noUnusedParameters": true,                       /* Raise an error when a function parameter isn't read. */// "exactOptionalPropertyTypes": true,               /* Interpret optional property types as written, rather than adding 'undefined'. */// "noImplicitReturns": true,                        /* Enable error reporting for codepaths that do not explicitly return in a function. */// "noFallthroughCasesInSwitch": true,               /* Enable error reporting for fallthrough cases in switch statements. */// "noUncheckedIndexedAccess": true,                 /* Add 'undefined' to a type when accessed using an index. */// "noImplicitOverride": true,                       /* Ensure overriding members in derived classes are marked with an override modifier. */// "noPropertyAccessFromIndexSignature": true,       /* Enforces using indexed accessors for keys declared using an indexed type. */// "allowUnusedLabels": true,                        /* Disable error reporting for unused labels. */// "allowUnreachableCode": true,                     /* Disable error reporting for unreachable code. *//* Completeness */// "skipDefaultLibCheck": true,                      /* Skip type checking .d.ts files that are included with TypeScript. */"skipLibCheck": true                                 /* Skip type checking all .d.ts files. */}
}

基础概念：

基础类型：字符串、数字、布尔

// 字符串
const str: string = 'abc'// 数字
const num: number = 123// 布尔
const bool: boolean = true

复杂类型：数组、对象

//数组
const arr: number[] = [1,2,3]
arr[0] = '0' // 报错 不能将 string 类型赋给 number类型
arr[0] = 0//对象
const obj: {x: number} = {x: 1, y: 1} //报错 不能将类型{x: number, y: number} 分配给类型 {x: number} 
const obj: {x: number } = {x: 1}
const obj: {x: number, y:number} = {x: 1, y: 1}//可选字段
const optionalObj: {x: number, y?:number} = {x: 1}
optionalObj.y = 'y' // 报错 不能将类型 string 分配给 类型 number。 此时 y?: number | undefined 组合类型联合
optionalObj.y = 2

对象类型：匿名、接口 interface、类型 type

//对象类型
//接口
interface  interfacename {str: string
}//类型别名
type typename = {str: string
}

函数 function

类 class

枚举 enum

类型推断 type inference

//类型推断, 没有对n做类型声明，值赋值同时确定变量类型
let n = 1let n = '1'

类型断言

// as string 给x.contents 声明类型，就可以使用该类型的一些方法
console.log(x.contents as string).toLowerCase()

泛型 generic：包括 泛型 对象类型、泛型 函数、泛型 类

// 泛型
interface Generic<Type> {test: Type
}

 特殊类型 ： void any unknown never

//any
const any: any = {}

...