nodejs 'util' is global sometimes?

Question

nodejs 'util' is global sometimes?

I have a model with a function call of util.endsWith(str, end) but I forgot to import my util file. Normally I would expect an error like:

cannot call method 'endsWith' of undefined or something like that

but the error I am getting is:

TypeError: Object #<Object> has no method 'endsWith'

which indicates that util is defined. I did a console.log of it and found that it is the same object you get from require('util').

I certainly did not require the util module in this, and I can't find anywhere in my files where I do so (not that I would expect something require-ed in another file to be in this file).

Interestingly, util is only defined if I require this module from somewhere else; if I just run the file then util is undefined.

Is this normal?

My files are not that complicated (<100 lines each) but I have not been able to replicate it with a super basic example. Maybe it has to be a couple of levels deep.

nodejs 0.10.12

node.js

Answer 1

Most likely you forgot doing var util somewhere in a different module where util is being assigned to. This results in a global variable being created.

You may be leaking more global variables this way. You can get an overview which globals are being created by doing:

var oldGlobalNames = Object.keys(global)

at top of main script. Then do

console.log(_.difference(Object.keys(global), oldGlobalNames))

on bottom.

This uses the difference function from Underscore.

Or use https://github.com/aheckmann/gleak module.

Another idea: do a project-wide search (including node_modules dir) for util =. Get a sense of where util is being assigned to.

See also Node.js - why do I get leaks when testing with mocha and zombie?

Answer 2

I think this is a repl vs script interpreter thing. When you run the repl (either node or coffee), indeed util is available as a pre-imported module it seems. However, when you run them and pass a script argument, util is not there:

node -e 'console.log(util)'

[eval]:1
console.log(util)
            ^
ReferenceError: util is not defined
    at [eval]:1:13
    at Object.<anonymous> ([eval]-wrapper:6:22)
    at Module._compile (module.js:456:26)
    at evalScript (node.js:532:25)
    at startup (node.js:80:7)
    at node.js:901:3

However, with the repl:

node
> util
{ format: [Function],
  deprecate: [Function],
  print: [Function],
  puts: [Function],......