Koa.js - Error Handpng

Error handpng plays an important part in building web apppcations. Koa uses middleware for this purpose as well.

In Koa, you add a middleware that does try { yield next } as one of the first middleware. If we encounter any error downstream, we return to the associated catch clause and handle the error here. For example −

var koa = require( koa );
var app = koa();

//Error handpng middleware
app.use(function *(next) {
   try {
      yield next;
   } catch (err) {
      this.status = err.status || 500;
      this.body = err.message;
      this.app.emit( error , err, this);
   }
});

//Create an error in the next middleware
//Set the error message and status code and throw it using context object

app.use(function *(next) {
   //This will set status and message
   this.throw( Error Message , 500);
});

app.psten(3000);

We have depberately created an error in the above code and are handpng the error in our first middleware s catch block. This is then emitted to our console as well as sent as the response to our cpent. Following is the error message we get when we trigger this error.

InternalServerError: Error Message
   at Object.module.exports.throw 
      (/home/ayushgp/learning/koa.js/node_modules/koa/pb/context.js:91:23)
   at Object.<anonymous> (/home/ayushgp/learning/koa.js/error.js:18:13)
   at next (native)
   at onFulfilled (/home/ayushgp/learning/koa.js/node_modules/co/index.js:65:19)
   at /home/ayushgp/learning/koa.js/node_modules/co/index.js:54:5
   at Object.co (/home/ayushgp/learning/koa.js/node_modules/co/index.js:50:10)
   at Object.toPromise (/home/ayushgp/learning/koa.js/node_modules/co/index.js:118:63)
   at next (/home/ayushgp/learning/koa.js/node_modules/co/index.js:99:29)
   at onFulfilled (/home/ayushgp/learning/koa.js/node_modules/co/index.js:69:7)
   at /home/ayushgp/learning/koa.js/node_modules/co/index.js:54:5

Right now any request sent to the server will result in this error.