Writing error-handler middleware functions

ExpressJS already includes by default a built-in error handler which gets executed at the end of all middleware and route handlers.

There are ways that the built-in error handler can be triggered. One is implicit when an error occurs inside a route handler. For example:

app.get('/', (request, response, next) => { 
    throw new Error('Oh no!, something went wrong!') 
}) 

And another way of triggering the built-in error handler is explicit when passing an error as an argument to next(error). For instance:

app.get('/', (request, response, next) => { 
    try { 
        throw new Error('Oh no!, something went wrong!') 
    } catch (error) { 
        next(error) 
    } 
}) 

The stack trace is displayed on the client side. If NODE_ENV is set to production, then the stack trace is not included.

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