Question about running js script in vm2

[dekhaus]

Question about running js script in vm2

[patriksimek]

I have updated the docs so the difference between VM and NodeVM should be clear now.

[patriksimek]

You can do that with vm2.

var vm = require('vm2');

var vm = new vm.VM();
vm.run('var dummy = 15;');
console.log(vm.run('dummy')); // Outputs 15

Your code doesn't work btw, throws:

ReferenceError: dummy is not defined

[dekhaus]

My example was a quick hack - let me be more specific.

Let's say we have a js file that contains the following js code

eval(userScript);

var results = [];

for (var i = 0 ; i < fooObjects.length; i++) {
  results.push(echo(i));
}

output = JSON.stringify(results);

Let's call this file 'helper.js'.

Additionally - users have the ability to supply their own js code that is meant to interact with the code in 'helper.js'. So - a user can supply the following js (this code is in a file called 'userScript.js' ) ...

function echo(num) {
  return doSomething(num) ;
}

function doSomething(num) {
  console.log("in 'doSomething' method.  'num' = " + num);
  return num * 2;
}

Using Node's existing VM - I can do the following in NodeJS ...

const fs = require('fs');
const vm = require('vm');

var helper = fs.readFileSync(__dirname + '/helper.js', { encoding: "utf8" });

var userScript = fs.readFileSync(__dirname + '/userScript.js', { encoding: "utf8" });

var sandbox = {
  input:      JSON.parse('[1,2,3]');
  output:     "",
  userScript: userScript,
  log:        [],
  console:    {
    log: function(arg) { sandbox.log.push(arg); }
  }
};

var context = vm.createContext(sandbox);
var script = new vm.Script(helper);

script.runInContext(context);

console.log('output', sandbox.output);  // prints a string representation of the json for the results array 
console.log('log', sandbox.log);        // prints the "in 'doSomething' method. 'num' = ..." messages that were added to the sandbox.log array by the doSomething method

This is obviously a contrived example - but the 'mechanics' of how the 'helper.js' code eval's the 'userScript.js' code is the same as in my working example. How can I do this using VW2 ?

Thanks
Dave

[patriksimek]

Hope it helps.

var vm = require('vm2');

var helper = 'var log = [], console = {log: function(msg) { log.push(msg) }}; (function() { eval(userScript); return {output: multiply(input), log: log} })();';
var userScript = 'function multiply(num) { console.log("test"); return num * 2; }';

var vm = new vm.VM({
    sandbox: {
        input: 5,
        userScript: userScript
    }
});

var result = vm.run(helper);

console.log(result.output);
console.log(result.log);

[dekhaus]

Hi

Using your instructions above - I was able to replicate the base functionality of the default 'vm' using vm2.

The next step is to be able to allow users to 'require' modules (I think they're called modules - I'm new to NodeJS).

Continuing the example above - let's say my user wants to use the 'requests' module/library to retrieve data from some webservice endpoints. I need to be able to do something like this (note the change in the userScript ...

var vm = require('vm2');

var helper = 'var log = [], console = {log: function(msg) { log.push(msg) }}; (function() { eval(userScript); return {output: multiply(input), log: log} })();';
var userScript = 'var request = require('request'); /* function which uses 'request' would go here * / function multiply(num) { console.log("test"); return num * 2; }';

var vm = new vm.VM({
    sandbox: {
        input: 5,
        userScript: userScript
    },
    require: true,
    requireExternal: true
});

var result = vm.run(helper);

console.log(result.output);
console.log(result.log);

When I try and run the above - what used to work (before I added the "var request = require('request');") no longer does. I get the following error ..

undefined:1
var request = require('request');
              ^
ReferenceError: require is not defined
    at eval (eval at <anonymous> (vm:5:10), <anonymous>:1:15)
    at vm:5:5
    at vm:22:2
    at VM.run (/Users/dekhaus/node_modules/vm2/lib/main.js:196:19)
    at executeScript (/Users/dekhaus/projects/django/itriage/node/server.js:111:22)
    at IncomingMessage.<anonymous> (/Users/dekhaus/projects/django/itriage/node/server.js:42:24)
    at emitNone (events.js:67:13)
    at IncomingMessage.emit (events.js:166:7)
    at endReadableNT (_stream_readable.js:893:12)
    at doNTCallback2 (node.js:430:9)

How do I call 'require' in my user supplied script ?

Thanks
Dave

[patriksimek]

You need to instantiate the vm.NodeVM class rather than vm.VM class.

[0o-de-lally]

@patriksimek
I'm struggling with this as well. Can you document the difference between vm.VM and vm.NodeVM ?

With the example:

var testVM = require('vm2').NodeVM;

var options = {
    require: true
};

var vm = new testVM(options);
var result = vm.run("require('request')");
console.log(result);

Throws the error:

throw new VMError("Access denied to require '" + modulename + "'", "

[NishchithBangar]

Hi @patriksimek , i m new to the concept of vm and i am in the middle of implementing a concept wrt vm2 utilization, but, i am finding it difficult to make the implementation since i have found very less documentation and examples on the usage of all its available options. (or may be i couldn't find the proper available resource). Kindly help me with the resources that i can refer in order to proceed with my implementation.