Koa 中的错误处理解析

app.use(async (ctx, next) => {
 try {
  await next();
 } catch (err) {
  ctx.status = err.status || 500;
  ctx.body = err.message;
  ctx.app.emit("error", err, ctx);
 }
});

+   ctx.app.emit('error', err, ctx);

app.on("error", (err, ctx) => {
 /* 错误的集中处理:
  * log 出来
  * 写入日志
  * 写入数据库
  *  ...
  */
});

const Koa = require("koa");
const app = new Koa();

app.use(async (ctx, next) => {
 try {
  await next();
 } catch (err) {
  const status = err.status || 500;
  ctx.status = status;
  ctx.type = "html";
  ctx.body = `
  <b>${status}</b> ${err}
  `;
  // emmit
  ctx.app.emit("error", err, ctx);
 }
});

app.use(ctx => {
 const a = "hello";
 a = "hello world!"; // TypeError: Assignment to constant variable.
 ctx.body = a;
});

app.on("error", (err, ctx) => {
 console.error("Ooops..\n", err);
});

app.listen(3000);

const err = new Error("err msg");
err.status = 401;
err.expose = true;
throw err;

ctx.throw(401, "err msg");

app.use(ctx => {
 ctx.throw(401, "access_denied", { user: { name: "foo" } });
});

app.on("error", (err, ctx) => {
 console.error("Ooops..\n", err.user);
});