serve index.html on 404

package.json

@@ -11,6 +11,7 @@
         "@types/koa": "^2.11.0",
         "@types/koa-logger": "^3.1.1",
         "@types/koa-router": "^7.0.42",
+        "@types/koa-send": "^4.1.2",
         "@types/koa-static": "^4.0.1",
         "@types/koa__cors": "^2.2.3",
         "@types/lodash": "^4.14.149",
@@ -38,24 +39,25 @@
         "tslint-plugin-prettier": "^2.0.1"
     },
     "dependencies": {
-        "ts-node": "8.5.4",
-        "tsconfig-paths": "^3.9.0",
-        "typescript": "3.7.3",
-        "concurrently": "^5.0.0",
-        "cross-env": "^6.0.3",
         "@koa/cors": "^3.0.0",
         "bcrypt": "^3.0.7",
+        "concurrently": "^5.0.0",
+        "cross-env": "^6.0.3",
         "jsonwebtoken": "^8.5.1",
         "koa": "^2.11.0",
         "koa-body": "^4.1.1",
         "koa-jwt": "^3.6.0",
         "koa-logger": "^3.2.1",
         "koa-router": "^7.4.0",
+        "koa-send": "^5.0.0",
         "koa-static": "^5.0.0",
         "lodash": "^4.17.15",
         "mysql": "^2.17.1",
         "reflect-metadata": "^0.1.13",
-        "typeorm": "0.2.21"
+        "ts-node": "8.5.4",
+        "tsconfig-paths": "^3.9.0",
+        "typeorm": "0.2.21",
+        "typescript": "3.7.3"
     },
     "cacheDirectories": [
         "frontend/node_modules",

src/app.ts

@@ -5,7 +5,9 @@ import * as Koa from "koa";
 import * as bodyParser from "koa-body";
 import * as jwt from "koa-jwt";
 import * as logger from "koa-logger";
+import * as send from "koa-send";
 import * as serve from "koa-static";
+
 import { config } from "~config";
 import { docsRouter } from "~routes/docs";
 import { userRouter } from "~routes/users";
@@ -21,11 +23,14 @@ app.use(
         passthrough: true,
     }),
 );
-app.use(serve("frontend/dist"));
 
 app.use(async (ctx, next) => {
     try {
         await next();
+        const status = ctx.status || 404;
+        if (status === 404) {
+            await send(ctx, "frontend/dist/index.html");
+        }
     } catch (err) {
         ctx.status = err.status || 500;
         ctx.body = err.message;
@@ -33,6 +38,8 @@ app.use(async (ctx, next) => {
     }
 });
 
+app.use(serve("frontend/dist"));
+
 app.use(userRouter.routes()).use(userRouter.allowedMethods());
 app.use(docsRouter.routes()).use(docsRouter.allowedMethods());