How to check if module function exist in Node js

Question

I have created a module and defined functions in it. Sometimes I need to check if a certain function is actually already created.

For example

var newyork = function() { 
   console.log("newyork");
};

var washington = function() { 
   console.log("washington");
};

exports.newyork = newyork;
exports.washington = washington;

Now in the different file, I want to first check if the function exists, something like:

var cities = require('./city');

if(cities.newyork) {
  console.log("city function exist");
}
else {
  //false
}

@JonasW. 1) [That](https://stackoverflow.com/questions/1995113/strangest-language-feature#answer-1998224) 2) [is](https://stackoverflow.com/questions/1995113/strangest-language-feature#answer-2003277) 3) [arguable](https://stackoverflow.com/questions/1995113/strangest-language-feature#answer-2003942). — Vanity Slug - codidact.com, Jul 24 '18 at 19:39

score 1 · Accepted Answer · answered Jul 24 '18 at 19:50

As I said in the comments what you wrote actually works because

if(cities.newyork){

Checks if cities.newyork is truthy. The following things are truthy:

functions (thats why it works here)
numbers except 0
strings except an empty one
objects / arrays

If it is however not defined, cities.newyork will be undefined which is falsy (will enter the else branch)

score 0 · Answer 2 · answered Jul 24 '18 at 19:34

0

typeof cities.cityName === 'function'

if city's name is assigned to some variable

typeof cities[cityName] === 'function'

answered Jul 24 '18 at 19:34

Zohaib Ijaz

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How to check if module function exist in Node js

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