什么是 HMR？
HMR 是hot module replacement 的简称，直译：热模块替换，如果不开启HMR模式，angular项目在模块更改的时候会从根节点开始刷新，开启HMR模式以后，只会刷新有修改的地方，开发效率在某种意义上可以提高
配置步骤
配置前提：你已经创建了一个angular6项目，安装hmr依赖
npm install --save-dev @angularclass/hmr
1）在 src/environments 目录下添加 environment.hmr.ts 配置文件，文件内容为:
export const environment = { production: false, hmr: true };
2）然后分别在 environment.prod.ts 和 environment.ts 添加 hmr:false 配置项
3）配置 src/tsconfig.app.json 文件 ，内容为：
"compilerOptions": { ... "types": ["node"] }
4）配置 src/hmr.ts 文件内容如下 ：
import { NgModuleRef, ApplicationRef } from "@angular/core";
import { createNewHosts } from "@angularclass/hmr";
export const hmrBootstrap = (
module: any,
bootstrap: () => Promise>
) => {
let ngModule: NgModuleRef;
module.hot.accept();
bootstrap().then(mod => (ngModule = mod));
module.hot.dispose(() => {
const appRef: ApplicationRef = ngModule.injector.get(ApplicationRef);
const elements = appRef.components.map(c => c.location.nativeElement);
const makeVisible = createNewHosts(elements);
ngModule.destroy();
makeVisible();
});
};
5）更新 src/main.ts 文件内容如下
import { enableProdMode } from "@angular/core";
import { platformBrowserDynamic } from "@angular/platform-browser-dynamic";
import { AppModule } from "./app/app.module";
import { environment } from "./environments/environment";
import { hmrBootstrap } from "./hmr";
if (environment.production) {
enableProdMode();
}
const bootstrap = () => platformBrowserDynamic().bootstrapModule(AppModule);
if (environment.hmr) {
if (module["hot"]) {
hmrBootstrap(module, bootstrap);
} else {
console.error("HMR is not enabled for webpack-dev-server!");
console.log("Are you using the --hmr flag for ng serve?");
}
} else {
bootstrap().catch(err => console.log(err));
}
6）配置 angular.json 文件 ：
"build": { "builder": "@angular-devkit/build-angular:browser", "options": { "outputPath": "dist/${project-name}", "index": "src/index.html", "main": "src/main.ts", "polyfills": "src/polyfills.ts", "tsConfig": "src/tsconfig.app.json", "assets": ["src/favicon.ico", "src/assets"], "styles": ["src/styles.css"], "scripts": [] }, "configurations": { "hmr": { "fileReplacements": [ { "replace": "src/environments/environment.ts", "with": "src/environments/environment.hmr.ts" } ] }, "production": { "fileReplacements": [ { "replace": "src/environments/environment.ts", "with": "src/environments/environment.prod.ts" } ], "optimization": true, "outputHashing": "all", "sourceMap": false, "extractCss": true, "namedChunks": false, "aot": true, "extractLicenses": true, "vendorChunk": false, "buildOptimizer": true } } }, ... "serve": { "builder": "@angular-devkit/build-angular:dev-server", "options": { "browserTarget": "${project-name}:build" }, "configurations": { "production": { "browserTarget": "${project-name}:build:production" }, "hmr": { "browserTarget": "${project-name}:build:hmr", "hmr": true } } },
7）启动方式:两种
第一种：
ng serve --configuration hmr
第二种:
ng run ${project-name}:serve:hmr
8)为方便一般添加在package.json的scripts里:
"scripts": { ... "hmr": "ng serve --configuration hmr --open" }