I have a module that writes to a log file. (coffeescript sorry, but you get the idea!)
require = patchRequire(global.require)
fs = require('fs')
exports.h =
log: ()->
for s in arguments
fs.appendFile "log.txt", "#{s}\n", (e)->
if (e) then throw e
It works file when I call it directly. But when I call it from a callback, for example casperjs start event:
h = require('./h').h
casper = require('casper').create()
casper.start "http://google.com", ()->
h.log("hi")
casper.run()
... I always get this or similar "undefined" TyepError:
TypeError: 'undefined' is not a function (evaluating 'fs.appendFile("log.txt", "" + s + "\n", function(e) {
if (e) {
throw e;
}
})')
Googling this doesn't give many clues!
CasperJS runs on PhantomJS (or SlimerJS) and uses its modules. It is distinct from nodejs. PhantomJS' fs module doesn't have an appendFile function.
Of course you can use fs.write(filepath, content, 'a'); to append to a file if used in casper. If you still want to use your module both in casper and node then you need to write some glue code like
function append(file, content, callback) {
if (fs.appendFile) {
fs.appendFile(file, content, callback);
} else {
fs.write(file, content, 'a');
callback();
}
}
I think the problem is with the coffeescript. Try using a splat parameter instead of relying on the arguments object.
log(statements...)
If that doesn't work, you might need to look at the javascript output or try the same thing in plain JavaScript and see if you get the same error.
Related
I have an program that susposed to load js to server side dynamically by url (for organizing js files)
app.get('/*',function(req,res){
... path etc. code
if(compare(list,path)){
const js = require('/Js/'+list.find(x => x.pageUrl == path).js)
js.run(req,res)
}
... more code there
}
but for some reason passed res doesnt work and i get res.send is not defined error
here is the other module that i get path from url and load it
exports.run = function run(req,res)
{
res.Send("test") //not defined for some reason
console.log(res) //it is not undefined, i see stuff
res.end()
}
Your code says res.Send instead of res.send.
I'm trying to find the file of included modules. From the main module, require.resolve('module') happily returns me the value of the main key from the module's package.json.
However, I would like to do this from a module that's been included via npm. If I simply call require.resolve('module'), it looks in the node_modules for this module, whereas I need to resolve it from the point of view of the running package.
According to the docs, require is actually module.require and module.parent returns the module that first required this one. Why then does module.parent.require.resolve('module') not work? I get ana
error:
TypeError: module.parent.require.resolve is not a function
Oddly though, console.log module.parent.require.toString() returns
function (path) {
assert(path, 'missing path');
assert(typeof path === 'string', 'path must be a string');
return Module._load(path, this, /* isMain */ false);
}
so it certainly looks like a function to me.
Anyone know what's going on? I've also tried require.main.require.resolve() and that does a very similar thing.
TypeError: module.parent.require.resolve is not a function
Oddly though, console.log module.parent.require.toString() returns ...
module.parent.require is a function, module.parent.require.resolve is not.
Why is resolve() not a function?
It appears require() and module.require() are not the same:
console.log(require === module.require); // false
For the curious:
console.log(module.require.toString())
function (path) {
assert(path, 'missing path');
assert(typeof path === 'string', 'path must be a string');
return Module._load(path, this, /* isMain */ false);
}
console.log(require.toString())
function require(path) {
try {
exports.requireDepth += 1;
return mod.require(path);
} finally {
exports.requireDepth -= 1;
}
}
So require() calls module.require(), but is not the same thing.
What about resolve()?
We know require.resolve is a function:
console.log(require.resolve.toString())
function resolve(request) {
return Module._resolveFilename(request, mod);
}
But module.require.resolve is not:
console.log(module.require.resolve)
undefined
So unfortunately resolve() is only available at require.resolve(), and not at module.require.resolve() (or module.parent.require.resolve() for that matter).
Solution?
Not a great solution, but you could try manually calling Module._resolveFilename() and passing in the parent module instead of the current module:
const Module = module.constructor;
const fileName = Module._resolveFilename('module', module.parent);
This solution isn't great because it relies on internal API functions that could possibly change in the future. It would be nice if NodeJS would provide better documentation and APIs for module loading/resolving.
I am requiring a module and saving it in a variable. But when I call a module function by wrong name, it does not throw any error or consoles any error. How do I make this throw error?
var module = require('../pre_process/' + preProcessFolder + '/' + preProcessModule);
// module -> { XYZ: [Function] }
//Following does not throw error and doesn't console anything.How to handle/debug this error
module['XY'](result, userId)
.then(function(recData) {
})
I am using q library for promise.
So you want to check if a function (provided by a modul) exists.
You could use try like the example here:
Javascript check if function exists
I'm loading a config.json file using require('./config.json') but I don't want to require a config file if they want to pass command line arguments instead, or just use the defaults. Is there any way to try to load a JSON file this way but not spit out an error if it can't be found?
For general modules, you can check for existence before trying to load. In the following path is whatever path you want to load and process() is a function performing whatever processing you'd like on your module:
var fs = require("fs");
fs.exists(path, function (exists) {
if (exists) {
var foo = require(path);
process(foo);
}
else {
// Whatever needs to be done if it does not exist.
}
});
And remember that path above must be an actual path, and not a module name to be later resolved by Node as a path.
For a JSON file specifically, with path and process having the same meanings as above:
fs.readFile(path, function (err, data) {
if (err) {
// Whatever you must do if the file cannot be read.
return;
}
var parsed = JSON.parse(data);
process(parsed);
});
You can also use try... catch but keep in mind that v8 won't optimize functions that have try... catch in them. With path and process meaning the same as above:
try {
var foo = require(path);
process(foo);
}
catch (e) {
if (e.code !== "MODULE_NOT_FOUND")
throw e; // Other problem, rethrow.
// Do what you need if the module does not exist.
}
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.
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);
}
});
You simply run require('test2.js'), and then call a function on the exported object. From the documentation on modules:
Node has a simple module loading system. In Node, files and modules are in one-to-one correspondence. As an example, foo.js loads the module circle.js in the same directory.
The contents of foo.js:
var circle = require('./circle.js');
console.log( 'The area of a circle of radius 4 is ' + circle.area(4));
The contents of circle.js:
var PI = Math.PI;
exports.area = function (r) {
return PI * r * r;
};
exports.circumference = function (r) {
return 2 * PI * r;
};
The module circle.js has exported the functions area() and circumference(). To export an object, add to the special exports object.
Note that exports is a reference to module.exports making it suitable for augmentation only. If you are exporting a single item such as a constructor you will want to use module.exports directly instead.
function MyConstructor (opts) {
//...
}
// BROKEN: Does not modify exports
exports = MyConstructor;
// exports the constructor properly
module.exports = MyConstructor;
Variables local to the module will be private. In this example the variable PI is private to circle.js.
The module system is implemented in the require("module") module.
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!