Load and execute external file in node.js

Question

is it easy/possible to run a node js file from another node js file? For instance, i'm having two files test1.js and test2.js. i want to execute the test1.js file from test2.js.

Answer 1

I think the better way to accomplish what you're trying to do would be to do what my other answer suggests. But to execute commands on the command line as your questions suggests, you want to use child_process.exec. For example:

var exec = require('child_process').exec,
    child;

child = exec('node test2.js {{args}}',
  function (error, stdout, stderr) {
    console.log('stdout: ' + stdout);
    console.log('stderr: ' + stderr);
    if (error !== null) {
      console.log('exec error: ' + error);
    }
});

Answer 2

There are different scenarios here - using modules, loading them "the right way" - it's the way to go when writing your own code.

What about "random" .js files, e.g. downloaded via web scraping? (If this is a good idea to execute them is beyond the scope of this answer...)

Well - you can just require them, if you're only interested in the side effects:

test2.js:

console.log('hello')

test1.js:

console.log('about to execute')
require('./test2.js')
console.log('done')

Note the ./ in require(). But, if you want to run it twice, this won't work:

test3.js:

console.log('about to execute twice?')
require('./test2.js')
require('./test2.js')
console.log('surprise')

This shows, that require works like a Python import - only executing the file if it hasn't been loaded yet. But - it's possible to circumvent it and force a reload: How to remove module after "require" in node.js?

test4.js:

console.log('about to execute twice!')
require('./test2.js')
delete require.cache[require.resolve('./test2.js')]
require('./test2.js')
console.log('NO surprise this time around')

The difference from a Python import is that you can't import anything unless it's exported. So you would have to change the required file and do something with module.exports.

If you're working with the node shell, there is an alternative:

test5.js:

console.log('the const below is private?')
const x = 5

And then:

$ node
> .load test5.js
console.log('the const below is private?')
const x = 5

the const below is private?
undefined
> x
5

Note that there are no quotes around filename in .load, and also no ./. This is somewhat verbose when used (echoing the loaded script). But it is at least some way of playing with the values the script creates.

Final warning: always be careful about what you're about to execute!