使用Typescript开发Node的技巧

typescript（以下简称为ts）是js的超集，它有独立的编译器，为js提供了很多种类型，能够避免js的鸭子类型所产生的类型错误，这种错误有时候是致命的，以至于难以发现。因此我们希望在node中也引入typescript，使程序的编写效率有大大的提高。

begin

首先我们需要安装typescript的tsc编译器，tsc能够把ts转换为js，因为node的解释器是不认ts的，因此在运行node应用之前需要把ts转换为js。

cnpm install --save typescript

等待安装完毕后可以查看一下tsc的版本

?  dist tsc -v
Version 2.6.1

开始一个小demo

安装完tsc ，我们就可以开始一个小demo了，新建一个node_project，把它作为node 的项目目录

mkdir node_project
cd node_project
npm init
...
tsc --init

npm init是把该目录初始化为一个npm项目，之后执行的tsc —init是为了让tsc帮助我们创建tsconfig文件，tsconfig是tsc每次编译时都会检查的一个配置文件。

tsconfig.json

{
  "compilerOptions": {
    /* Basic Options */
    "target": "es5",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', or 'ESNEXT'. */
    "module": "commonjs",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 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', or 'react'. */
    // "declaration": true,                   /* Generates corresponding '.d.ts' file. */
    // "sourceMap": true,                     /* Generates corresponding '.map' file. */
    // "outFile": "./",                       /* Concatenate and emit output to single file. */
    "outDir": "./dist",                        /* Redirect output structure to the directory. */
    "rootDir": "./src",                       /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
    // "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. */
    // "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. */

    /* 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. */
    // "preserveSymlinks": true,              /* Do not resolve the real path of symlinks. */

    /* Source Map Options */
    // "sourceRoot": "./",                    /* Specify the location where window should locate TypeScript files instead of source locations. */
    // "mapRoot": "./",                       /* Specify the location where window 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. */
  }
}

这里只需关注一下outDir和rootDir。outDir是tsc编译后输出的js文件的目录，这里我把它输出在dist目录，rootDir是源文件的目录，也就是需要被tsc编译的目录。

我们可以在src目录下编写一个简单的node程序

cd src 
touch main.ts

main.ts

import * as http from 'http';
import { IncomingMessage, ServerResponse } from 'http';

let httpServer:http.Server = http.createServer((req:IncomingMessage,res:ServerResponse) => {
    res.writeHead(200);
    res.end('Hello Typescript!');
});

httpServer.listen(9999,() => console.log('listening'));

然后我们可以让tsc开启监视模式，根据源文件目录下的文件改变来编译ts文件

tsc -w

现在开始执行main.ts

cd dist
node main.js

可以看到运行成功！

总结

这样虽然还是会有点麻烦，每次都要用node main.js来运行node程序，其实我们完全可以引入webpack来进行模块热更新，如果你需要的话。