Import a Node.js module function, without invoking it

Question

I have a Node.js module with a function that is exported, and designed to be invoked when the script is run from the command line:

function init() {
  console.log('initializing');
}
init();

module.exports = { init };

I'd like to require / import the underlying method in another module, without evaluating init. Unfortunately require seems to evaluate it:

> require('./test.js').init;
initializing
{ init: [Function: init] }

Is it possible to require this method, without evaluating it in this scenario?

sleighty · Accepted Answer · 2019-03-13T00:32:40.000

How about putting the part you need to run when the script is invoked from the command line inside a check for require.main === module? That way, init() is only called if you're invoking that script using node test.js. So:

function init() {
    console.log('initializing');
}

if (require.main === module) {
    init();
}

module.exports = { init };

It kind of answers your question backwards, but I think this might be close to what you're looking for.

You might want to keep an eye out for changes to this feature with regards to the --experimental-modules flag.

score 2 · Answer 2 · answered Mar 12 '19 at 23:55

2

Your issue is related to the fact that you invoke the init function yourself. Just do not invoke it in the module which contains implementation instead invoke the function after requiring it inside any other module.

function init() {
  console.log('initializing');
}
// warning! do not call invoke init function here
// init()

module.exports = { init };

answered Mar 12 '19 at 23:55

Alex

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I specifically need to invoke it in this use-case – Allyl Isocyanate Mar 12 '19 at 23:56
Mind expanding on the use-case? As it stands there's no way to parse a module without parsing every statement and that includes the call to `init()` – sleighty Mar 13 '19 at 00:08
1

In this case, it will be always invoked since it is located in a module global scope. – Alex Mar 13 '19 at 00:08

score 1 · Answer 3 · answered Mar 13 '19 at 00:31

This means that init() shouldn't be executed automatically, and there should be different entry points.

One entry point for programmatic use (test.js). Another one to be used as command-line executable (test-cli.js):

require('./test.js').init()

This is a common scenario for NPM packages. CLI entry point can be specified in package bin.

Import a Node.js module function, without invoking it

3 Answers3