概览
刚开始可能觉得 TypeScritp 会很麻烦，会多写很多额外代码，这只是因为对 TypeScript 掌握的还不够，在我看来掌握 TypeScript 至少具有以下好处：
- 减少、避免错误的发生
- 使 IDE 具有代码提示功能
- 各大框架都基本集成了 Typescript，不会 TypeScript，看框架源码会很吃力
- 个人进阶必会技能，面试加分
TypeScript 只是在编译阶段对源码进行检测、编译，编译生成的代码依旧是浏览器能够“读懂”的，不会包含 TypeScript 中的特性语法，如源码 let name: string = 'Jack'，编译后输出 let name = 'Jack'。
下面从头开始创建一个 TypeScript 项目。
创建项目文件夹
创建项目文件夹并初始化 package.json。
sh
mkdir ts-demo
cd ts-demo
pnpm init添加 TypeScript 配置文件
创建默认配置文件：
sh
npx tsc --inittsconfig.json:
json
{
"compilerOptions": {
/* Visit https://aka.ms/tsconfig.json to read more about this file */
/* Basic Options */
// "incremental": true, /* Enable incremental compilation */
"target": "es5", /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
"module": "commonjs", /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'. */
// "lib": [], /* Specify library files to be included in the compilation. */
// "allowJs": true, /* Allow javascript files to be compiled. */
// "checkJs": true, /* Report errors in .js files. */
// "jsx": "preserve", /* Specify JSX code generation: 'preserve', 'react-native', 'react', 'react-jsx' or 'react-jsxdev'. */
// "declaration": true, /* Generates corresponding '.d.ts' file. */
// "declarationMap": true, /* Generates a sourcemap for each corresponding '.d.ts' file. */
// "sourceMap": true, /* Generates corresponding '.map' file. */
// "outFile": "./", /* Concatenate and emit output to single file. */
// "outDir": "./", /* Redirect output structure to the directory. */
// "rootDir": "./", /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
// "composite": true, /* Enable project compilation */
// "tsBuildInfoFile": "./", /* Specify file to store incremental compilation information */
// "removeComments": true, /* Do not emit comments to output. */
// "noEmit": true, /* Do not emit outputs. */
// "importHelpers": true, /* Import emit helpers from 'tslib'. */
// "downlevelIteration": true, /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
// "isolatedModules": true, /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */
/* Strict Type-Checking Options */
"strict": true, /* Enable all strict type-checking options. */
// "noImplicitAny": true, /* Raise error on expressions and declarations with an implied 'any' type. */
// "strictNullChecks": true, /* Enable strict null checks. */
// "strictFunctionTypes": true, /* Enable strict checking of function types. */
// "strictBindCallApply": true, /* Enable strict 'bind', 'call', and 'apply' methods on functions. */
// "strictPropertyInitialization": true, /* Enable strict checking of property initialization in classes. */
// "noImplicitThis": true, /* Raise error on 'this' expressions with an implied 'any' type. */
// "alwaysStrict": true, /* Parse in strict mode and emit "use strict" for each source file. */
/* Additional Checks */
// "noUnusedLocals": true, /* Report errors on unused locals. */
// "noUnusedParameters": true, /* Report errors on unused parameters. */
// "noImplicitReturns": true, /* Report error when not all code paths in function return a value. */
// "noFallthroughCasesInSwitch": true, /* Report errors for fallthrough cases in switch statement. */
// "noUncheckedIndexedAccess": true, /* Include 'undefined' in index signature results */
// "noPropertyAccessFromIndexSignature": true, /* Require undeclared properties from index signatures to use element accesses. */
/* Module Resolution Options */
// "moduleResolution": "node", /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
// "baseUrl": "./", /* Base directory to resolve non-absolute module names. */
// "paths": {}, /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
// "rootDirs": [], /* List of root folders whose combined content represents the structure of the project at runtime. */
// "typeRoots": [], /* List of folders to include type definitions from. */
// "types": [], /* Type declaration files to be included in compilation. */
// "allowSyntheticDefaultImports": true, /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
"esModuleInterop": true, /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
// "preserveSymlinks": true, /* Do not resolve the real path of symlinks. */
// "allowUmdGlobalAccess": true, /* Allow accessing UMD globals from modules. */
/* Source Map Options */
// "sourceRoot": "", /* Specify the location where debugger should locate TypeScript files instead of source locations. */
// "mapRoot": "", /* Specify the location where debugger should locate map files instead of generated locations. */
// "inlineSourceMap": true, /* Emit a single file with source maps instead of having a separate file. */
// "inlineSources": true, /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */
/* Experimental Options */
// "experimentalDecorators": true, /* Enables experimental support for ES7 decorators. */
// "emitDecoratorMetadata": true, /* Enables experimental support for emitting type metadata for decorators. */
/* Advanced Options */
"skipLibCheck": true, /* Skip type checking of declaration files. */
"forceConsistentCasingInFileNames": true /* Disallow inconsistently-cased references to the same file. */
}
}生成的配置文件中有一些默认的配置和一些说明描述，修改配置如下：
json
{
"compilerOptions": {
"target": "es5", /* 编译之后生成的js文件需要遵循的标准 */
"noImplicitAny": false, /* 为false时，如果编译器无法根据变量的使用来判断类型时，将用any类型代替。为true时，将进行强类型检查，无法推断类型时，提示错误 */
"module": "commonjs", /* 遵循的JavaScript模块规范 */
"removeComments": true, /* 编译生成的JavaScript文件是否移除注释 */
"sourceMap": false, /* 编译时是否生成对应的source map文件。这个文件主要用于前端调试。当前端js文件被压缩引用后，出错时可借助同名的source map文件查找源文件中错误位置 */
"outDir": "js" /* 编译输出JavaScript文件存放的文件夹 */
},
"include":["ts"], /* 编译时需要包含的文件夹 */
"exclude": ["js"] /* 编译时需要剔除的文件夹 */
}当 target 设置为 es3 或 es5，module 默认使用 commonjs，当 target 为其他值时，module 默认es2015。
module 选项用来手动指定生成哪种模块化系统的代码，可设置的值有 none、commonjs、amd、udm、es2015（写成 es6、ES6、ES2015也可以）、es2020、ESNext。
添加源文件
Preview
/ts：TypeScript 源码文件存放的文件夹
/js：编译之后生成的 JavaScript 文件存放的文件夹
::: code-tabs
@tab demo.ts
ts
class Demo {
a: number;
b: number;
constructor(a: number, b: number) {
this.a = a
this.b = b
}
sum(): number {
return this.a + this.b
}
}
export { Demo }@tab app.ts
ts
import { Demo } from './models/demo'
const demo = new Demo(1, 2)
console.log(demo.sum()):::
编译源文件
编译器将按照配置文件编译源文件，会在文件夹 js 下面生成相应的文件夹及文件：
sh
npx tsc
Preview
::: code-tabs
@tab demo.js
js
"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.Demo = void 0;
var Demo = (function () {
function Demo(a, b) {
this.a = a;
this.b = b;
}
Demo.prototype.sum = function () {
return this.a + this.b;
};
return Demo;
}());
exports.Demo = Demo;@ app.js
js
"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var demo_1 = require("./models/demo");
var demo = new demo_1.Demo(1, 2);
console.log(demo.sum());:::
如果在根目录下执行的命令是tsc ts/app.ts，编译后的文件将放在相应源文件同目录下，js 文件夹下将不会有编译产物，也就是说此时并没有使用配置文件
Preview