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.
}
Related
I want to change the name of file when i get duplicate files while performing copy operation in nodejs using fs module (right now the process exits with error, i want to execute file name change logic on error)
function copyFile(filePath,fileName){
fs.copyFileSync(filePath,
path.join(destination,fileName),fs.constants.COPYFILE_EXCL, (err) => {
if (err) {
fileName= "0"+fileName; //changing the filename
copyFile(filePath,fileName)
}
console.log(fileName+" copied");
})
}
You simply need to check if error.code === 'EEXIST'.
Few notes:
copyFileSync does not accept callback - it's a synchronous function
You're using path.join incorrectly. This utility is used mainly to provide cross-platform paths (Unix - /, Windows - \). If you're concatenating it yourself with / there is no point to use path.join it will not work on non-unix systems anyway.
There is a typo filename -> fileName
You need two fileName... arguments for copyFile function (source and destination), because source file with prepended 0-s not exists by the moment you're calling the function.
const fs = require('fs');
const path = require('path');
const destination = '/tmp/';
function copyFile(filePath, fileNameFrom, fileNameTo=fileNameFrom) {
const from = path.join(filePath, fileNameFrom);
const to = path.join(destination, fileNameTo);
try {
fs.copyFileSync(from, to, fs.constants.COPYFILE_EXCL);
console.log(`${from} copied into ${to}`);
} catch (error) {
console.error(error);
if (error.code === 'EEXIST') {
copyFile(filePath, fileNameFrom, '0' + fileNameTo);
}
}
}
copyFile('/tmp/test', 'a.txt');
Note: do not forget to change destination variable
O/S is ubuntu 16, node version is 4.2.6.
I have source / development code and run / distribution code, the source.js files are minified and mangled to create equivalent source.min.js files, and I would like for node js require to automatically search for .min.js files as well as .js files.
But as I have a lot of files, I would prefer not to have to go through every require in every file and instead modify the built-in require() function.
This is a very simple implementation of a stand alone function, but how can I modify the built-in function to behave the same way ?
function require(file){
try{return require(file)}
catch(e){return require(file+='.min.js')}
}
You can achieve this by modifying prototype function require of Module class and apply it globally
Here is how you can do it :
var pathModule = require('path');
var assert = require('assert').ok;
module.constructor.prototype.require = function (path) {
var self = this;
assert(typeof path === 'string', 'path must be a string');
assert(path, 'missing path');
try {
return self.constructor._load(path, self);
} catch (err) {
// if module not found, we have nothing to do, simply throw it back.
if (err.code === 'MODULE_NOT_FOUND') {
throw err;
}
// resolve the path to get absolute path
path = pathModule.resolve(__dirname, path+".min.js")
// Write to log or whatever
console.log('Error in file: ' + path);
}
}
I need to check if file/(custom)module js exists under some path. I tried like
var m = require('/home/test_node_project/per');
but it throws error when there is no per.js in path.
I thought to check with
fs if file exists but I don't want to add '.js' as suffix if is possible to check without that.
How to check in node if module exists and if exists to load ?
Require is a synchronous operation so you can just wrap it in a try/catch.
try {
var m = require('/home/test_node_project/per');
// do stuff
} catch (ex) {
handleErr(ex);
}
You can just try to load it and then catch the exception it generates if it fails to load:
try {
var foo = require("foo");
}
catch (e) {
if (e instanceof Error && e.code === "MODULE_NOT_FOUND")
console.log("Can't load foo!");
else
throw e;
}
You should examine the exception you get just in case it is not merely a loading problem but something else going on. Avoid false positives and all that.
It is possible to check if the module is present, without actually loading it:
function moduleIsAvailable (path) {
try {
require.resolve(path);
return true;
} catch (e) {
return false;
}
}
Documentation:
require.resolve(request[, options])
Use the internal require() machinery to look up the location of a module, but rather than loading the module, just return the resolved filename.
Note: Runtime checks like this will work for Node apps, but they won't work for bundlers like browserify, WebPack, and React Native.
You can just check is a folder exists by using methods:
var fs = require('fs');
if (fs.existsSync(path)) {
// Do something
}
// Or
fs.exists(path, function(exists) {
if (exists) {
// Do something
}
});
I am trying to modify require like this
require = function (path) {
try {
return module.require(path);
} catch (err) {
console.log(path)
}
}
However, scope of this modification is only in the current module. I want to modify it globally, so every module that is required by this module will also get the same copy of require function.
Basically, I want to catch SyntaxError to know which file has problem. I can't seem to find any other alternative. If I put module.require in try/catch block, I'll be able to get the file name which caused SyntaxError.
I managed to solve it by modifying prototype function require of Module class. I put this in the main script and its available to all the required modules.
var pathModule = require('path');
var assert = require('assert').ok;
module.constructor.prototype.require = function (path) {
var self = this;
assert(typeof path === 'string', 'path must be a string');
assert(path, 'missing path');
try {
return self.constructor._load(path, self);
} catch (err) {
// if module not found, we have nothing to do, simply throw it back.
if (err.code === 'MODULE_NOT_FOUND') {
throw err;
}
// resolve the path to get absolute path
path = pathModule.resolve(__dirname, path)
// Write to log or whatever
console.log('Error in file: ' + path);
}
}
Why don't you use a try-catch block inside your code and once an error occurs to check the stack trace. Check out these links
How to print a stack trace in Node.js?
http://machadogj.com/2013/4/error-handling-in-nodejs.html
I can't seem to get any search results that explain how to do this.
All I want to do is be able to know if a given path is a file or a directory (folder).
The following should tell you. From the docs:
fs.lstatSync(path_string).isDirectory()
Objects returned from fs.stat() and fs.lstat() are of this type.
stats.isFile()
stats.isDirectory()
stats.isBlockDevice()
stats.isCharacterDevice()
stats.isSymbolicLink() // (only valid with fs.lstat())
stats.isFIFO()
stats.isSocket()
NOTE:
The above solution will throw an Error if; for ex, the file or directory doesn't exist.
If you want a true or false approach, try fs.existsSync(dirPath) && fs.lstatSync(dirPath).isDirectory(); as mentioned by Joseph in the comments below.
Update: Node.Js >= 10
We can use the new fs.promises API
const fs = require('fs').promises;
(async() => {
const stat = await fs.lstat('test.txt');
console.log(stat.isFile());
})().catch(console.error)
Any Node.Js version
Here's how you would detect if a path is a file or a directory asynchronously, which is the recommended approach in node.
using fs.lstat
const fs = require("fs");
let path = "/path/to/something";
fs.lstat(path, (err, stats) => {
if(err)
return console.log(err); //Handle error
console.log(`Is file: ${stats.isFile()}`);
console.log(`Is directory: ${stats.isDirectory()}`);
console.log(`Is symbolic link: ${stats.isSymbolicLink()}`);
console.log(`Is FIFO: ${stats.isFIFO()}`);
console.log(`Is socket: ${stats.isSocket()}`);
console.log(`Is character device: ${stats.isCharacterDevice()}`);
console.log(`Is block device: ${stats.isBlockDevice()}`);
});
Note when using the synchronous API:
When using the synchronous form any exceptions are immediately thrown.
You can use try/catch to handle exceptions or allow them to bubble up.
try{
fs.lstatSync("/some/path").isDirectory()
}catch(e){
// Handle error
if(e.code == 'ENOENT'){
//no such file or directory
//do something
}else {
//do something else
}
}
Seriously, question exists five years and no nice facade?
function isDir(path) {
try {
var stat = fs.lstatSync(path);
return stat.isDirectory();
} catch (e) {
// lstatSync throws an error if path doesn't exist
return false;
}
}
Depending on your needs, you can probably rely on node's path module.
You may not be able to hit the filesystem (e.g. the file hasn't been created yet) and tbh you probably want to avoid hitting the filesystem unless you really need the extra validation. If you can make the assumption that what you are checking for follows .<extname> format, just look at the name.
Obviously if you are looking for a file without an extname you will need to hit the filesystem to be sure. But keep it simple until you need more complicated.
const path = require('path');
function isFile(pathItem) {
return !!path.extname(pathItem);
}
If you need this when iterating over a directory (Because that's how I've found this question):
Since Node 10.10+, fs.readdir has a withFileTypes option which makes it return directory entry fs.Dirent instead of strings. Directory entries has a name property, and useful methods such as isDirectory or isFile, so you don't need to call fs.lstat explicitly.
import { promises as fs } from 'fs';
// ./my-dir has two subdirectories: dir-a, and dir-b
const dirEntries = await fs.readdir('./my-dir', { withFileTypes: true });
// let's filter all directories in ./my-dir
const onlyDirs = dirEntries.filter(de => de.isDirectory()).map(de => de.name);
// onlyDirs is now [ 'dir-a', 'dir-b' ]
Here's a function that I use. Nobody is making use of promisify and await/async feature in this post so I thought I would share.
const promisify = require('util').promisify;
const lstat = promisify(require('fs').lstat);
async function isDirectory (path) {
try {
return (await lstat(path)).isDirectory();
}
catch (e) {
return false;
}
}
Note : I don't use require('fs').promises; because it has been experimental for one year now, better not rely on it.
The answers above check if a filesystem contains a path that is a file or directory. But it doesn't identify if a given path alone is a file or directory.
The answer is to identify directory-based paths using "/." like --> "/c/dos/run/." <-- trailing period.
Like a path of a directory or file that has not been written yet. Or a path from a different computer. Or a path where both a file and directory of the same name exists.
// /tmp/
// |- dozen.path
// |- dozen.path/.
// |- eggs.txt
//
// "/tmp/dozen.path" !== "/tmp/dozen.path/"
//
// Very few fs allow this. But still. Don't trust the filesystem alone!
// Converts the non-standard "path-ends-in-slash" to the standard "path-is-identified-by current "." or previous ".." directory symbol.
function tryGetPath(pathItem) {
const isPosix = pathItem.includes("/");
if ((isPosix && pathItem.endsWith("/")) ||
(!isPosix && pathItem.endsWith("\\"))) {
pathItem = pathItem + ".";
}
return pathItem;
}
// If a path ends with a current directory identifier, it is a path! /c/dos/run/. and c:\dos\run\.
function isDirectory(pathItem) {
const isPosix = pathItem.includes("/");
if (pathItem === "." || pathItem ==- "..") {
pathItem = (isPosix ? "./" : ".\\") + pathItem;
}
return (isPosix ? pathItem.endsWith("/.") || pathItem.endsWith("/..") : pathItem.endsWith("\\.") || pathItem.endsWith("\\.."));
}
// If a path is not a directory, and it isn't empty, it must be a file
function isFile(pathItem) {
if (pathItem === "") {
return false;
}
return !isDirectory(pathItem);
}
Node version: v11.10.0 - Feb 2019
Last thought: Why even hit the filesystem?
I could check if a directory or file exists using this:
// This returns if the file is not a directory.
if(fs.lstatSync(dir).isDirectory() == false) return;
// This returns if the folder is not a file.
if(fs.lstatSync(dir).isFile() == false) return;
Function that returns type
I like coffee
type: (uri)-> (fina) ->
fs.lstat uri, (erro,stats) ->
console.log {erro} if erro
fina(
stats.isDirectory() and "directory" or
stats.isFile() and "document" or
stats.isSymbolicLink() and "link" or
stats.isSocket() and "socket" or
stats.isBlockDevice() and "block" or
stats.isCharacterDevice() and "character" or
stats.isFIFO() and "fifo"
)
usage:
dozo.type("<path>") (type) ->
console.log "type is #{type}"