CODEWITHSUNDEEP
node.jscommand-line-interfaceread-eval-print-loop
balanza
balanza

Reputation: 1079

nodejs REPL output on same line

I'm building a CLI app with nodejs with native REPL. A dumb sample is:

const repl = require('repl')
const myApp = require('myApp')
repl.start({
  eval: (input, context, filename, callback) => {
      const result = myApp(input)
      callback(null, result)
  },
  writer: (result) => result 
         ? 'my result: ' + result
         : ''  // <--- empty result
})

Everything is fine, but a newline is created for every response of the app. I'd like to override this behavior, and decide whether to create a new line or not.

Example Let's pretend the app to be a calculator:

$ node index.js
add 5
add 3
result
8

Because add command doesn't have any result, a new command should be inserted in the very next line. However, what I'm getting from the above code is:

$ node index.js
add 5

add 3

result
8

with an empty line added after any 0add call.

How can I prevent this?

Upvotes: 0

Views: 254

Answers (1)

balanza
balanza

Reputation: 1079

So I found out there's a parameter I could set, ignoreUndefined. If true, when you call callback(null, undefined) (empty result case), it won't add a new line.

Thus, in the above example:

const repl = require('repl')
const myApp = require('myApp')
repl.start({
  ignoreUndefined: true,
  eval: (input, context, filename, callback) => {
      const result = myApp(input)
      callback(null, result)
  },
  writer: (result) => result 
         ? 'my result: ' + result
         : undefined  // <--- empty result
})

docs: https://nodejs.org/api/repl.html

similar question: node.js REPL "undefined"

Upvotes: 1

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