Running a javascript function in node.js

[Rohit Harchandani]

Hi, I have just started playing around with node.js for a project. I parsed a JSON object which had a javascript function and when I tried to execute the function on the node.js server, I kept getting this error:

ReferenceError: require is not defined

I am sure i parsed the JSON object correctly to get the function, but not sure how to run this function. 

Thanks,

Rohit

[Paul Spaulding]

You can attach functions to an Object in JavaScript, but you cannot serialize/deserialize functions inside JavaScript Objects using JSON (at least not without extra meta-programming).  Functions are not one of the basic JSON types (Number, String, Boolean, Array, Object, null).

var a = {foo: function () {console.log('Hello');}};
JSON.stringify(a); // yields "{}"

[Jose Luis Rivas]

'require' is not defined. I think it's pretty clear.

If you show what the function does it may be easier but if I were you I
would be looking, in the meantime, where in the function I'm using
require and if I'm using it right.

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[Ryan Schmidt]

The JSON format does not accommodate functions, only data.

Perhaps you should show us some code so that we can more easily understand the problem you're encountering.

[Rohit Harchandani]

Hi,

This is the code that I am using to parse the JSON string.

var recData = JSON.parse(recDataString, function (key, value) {

    if (value && (typeof value === 'string') && value.indexOf("function") === 0) {

        var jsFunc = new Function('return ' + value)();

        return jsFunc;

    }

    return value;

});

console.log( "Type: " + typeof recData["runFunction"] )

runFunction in the json is a function which is something like this:

function() {

    require("fs");

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[Rohit Harchandani]

Sorry, I sent the msg without completing it, but the function gets parsed correctly, but i am not able to execute the function. Not sure why require should be undefined?

[Conrad Pankoff]

This is almost definitely a very, very bad idea. Instead of trying to serialise your code into JSON, you can just put it in a regular JavaScript file and require() it. For example, instead of this:

// code.json
{"myFunction":"function(a) { console.log(a); }"}

var code = JSON.parse(fs.readFileSync("./code.json"));
/* magic, insecure function stuff from your post */
code.myFunction("hello");

Do this:

// code.js
exports.myFunction = function(a) { console.log(a); }

var code = require("./code.js");
/* look ma, no magic */
code.myFunction("hello");

I shudder to think of why you might be doing things the way you are - are you trying to fetch code from somewhere else and run it?

[Rebecca Turner]

I think that there's a syntax error in the source to the function you're passing in, because your code works for me.

var recDataString = JSON.stringify({

    function: 'function () {var fs = require("fs"); console.log("did stuff") }'

});

var recData = JSON.parse(recDataString, function (key,value) {

    if (value && (typeof value === 'string') && value.indexOf("function") === 0) {

        var jsFunc = new Function('return ' + value)();

        return jsFunc;

    }

    return value;

});

> recData

{ function: [Function] }

> recData.function();

did stuff

undefined

And:

var recData = JSON.parse(recDataString, function (key, value) {

    if (value && (typeof value === 'string') && value.indexOf("function") === 0) {

        var jsFunc = new Function('return ' + value)();

        return jsFunc;

    }

    return value;

});

console.log( "Type: " + typeof recData["runFunction"] )

runFunction in the json is a function which is something like this:

But "runFunction".indexOf("function") !== 0, so it'll never be inflated.

-- Rebecca

[Ryan Schmidt]

On Jul 24, 2014, at 11:18 AM, Rohit Harchandani <rha...@gmail.com> wrote:

> Hi,
> This is the code that I am using to parse the JSON string.
>
> var recData = JSON.parse(recDataString, function (key, value) {
> if (value && (typeof value === 'string') && value.indexOf("function") === 0) {
> var jsFunc = new Function('return ' + value)();
> return jsFunc;
> }
> return value;
> });
>
> console.log( "Type: " + typeof recData["runFunction"] )
>
> runFunction in the json is a function which is something like this:
>
> function() {
> require("fs");

Could you show us sample json input? It's much easier for us to help you if you give us enough information to easily reproduce the problem on our own systems.

[Rohit Harchandani]

@Conrad - yes, i am trying this out on the same node.js server now. but eventually the goal is to ship the code to a node.js client where the sent code could run. Earlier I did write it to a file and then 'require' it. That obviously works. Are there better methods of doing this? 

@Ryan - This is a simpler json string example below. This too does not work for me when i run: recData["runFunction"]();

{"runFunction":"function(){'use strict';\nvar net = require(\"net\");\n\nconsole.log(\"NET\");\n}"}

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[Rebecca Turner]

Rohit,

@Ryan - This is a simpler json string example below. This too does not work for me when i run: recData["runFunction"]();

{"runFunction":"function(){'use strict';\nvar net = require(\"net\");\n\nconsole.log(\"NET\");\n}"}

Try it yourself on the console as I do here and see what you get. I say this because I don't see any problems, see below. Or, alternatively, maybe you need to be clearer about what you mean by "does not work".

> var recDataString = JSON.stringify({
... "runFunction": "function(){'use strict';\nvar net = require(\"net\");\n\nconsole.log(\"NET\");\n}"
... });
> var recData = JSON.parse(recDataString, function (key,value) {
... if (value && (typeof value === 'string') && key.indexOf("runFunction") === 0) {
..... return new Function('return ' + value)();
..... }
... return value;
... });
> recData
{ runFunction: [Function] }
> recData["runFunction"]()
NET
>  

[Alex Kocharin]

 

```

var func = vm.runInNewContext('(function(){\'do not use strict\';\nvar net = require(\"net\");\n\nconsole.log(\"NET\");\n})', {require: require, console: console})

func()

```

 

That said, passing require to external code is unsafe, so you'll probably want to whitelist modules that code is allowed to require.

 

 

26.07.2014, 04:30, "Rohit Harchandani" <rha...@gmail.com>:

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