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HomeBlogWeb DevelopmentPlaying With Nodejs Console
Many of the readers might already aware/heard of Node.js but for ones who wanted to get a quick refresher of Node.js, following along.
Node.js is associated with the following words:
Shorter definition of Node.js is - it is an open-source, cross-platform JavaScript run-time environment (Google Chrome's V8 Engine) that executes JavaScript code outside of a browser. Let’s developers use JavaScript to write command line tools and for server-side scripting—running scripts server-side to produce dynamic web page content before the page is sent to the user's web browser.
Node.js is majorly used for the following scenarios:
With all the advantages mentioned, Node.js is great in prototyping and agile developments, building superfast and highly scalable services. Are there any real time users who gained from Node.js? Yes, in fact there are hundreds of companies using and few to mention are
May be now with the proven record of node.js usage, is everyone using it for the above advantages majorly or there are any other simple command line apps and utilities? Yes, there are many and let’s list down few of them which might be useful in day-to-day work.
{ "name": "consolemoduleexamples", "version": "1.0.0", "description": "", "main": "index.js", "scripts": { "test": "echo \"Error: no test specified\" && exit 1" }, “type”: “module”, "author": "", "license": "ISC" }
Create an index.js file and add the below content.
console.log('Hello world');
Run node index.js to see the ‘Hello world’ response in terminal.
Note: For the below examples, make sure to install the specific module before running the example like npm install npm-name. Also, if there is a warning related to ES module, set "type": "module" in the package.json or use the .mjs extension.
import npmName from 'npm-name'; // Check a package name console.log(await npmName('npm-name')); // returns false // Check an organization name console.log(await npmName('@consolemoduleexamples')); // returns true
import cpy from 'cpy'; await cpy(['src/*.png', '!src/liger.png'], 'dist'); console.log('files copied successfully!');
Note: To verify this code, make sure to create two folders inside the project with name src and dist. With src containing files namely tiger.png, lion.png and liger.png. Post execution, tiger.png and lion.png files should be copied to dist as shown below.
‘empty-trash’ for cleaning up the Trash.
import emptyTrash from 'empty-trash'; await emptyTrash(); console.log('Trash cleaned!');
import wifiPassword from 'wifi-password'; const password = await wifiPassword(); console.log(password);
Note: When executing this code, OS will request for access permissions.
And many more...
get-stdin’ - this utility helps in simplifying work with stdin by getting it as a string or buffer.
import getStdin from 'get-stdin'; const str = await getStdin(); console.log(str);
import stringWidth from 'string-width'; console.log(stringWidth('平仮名')); // 6 console.log(stringWidth('a')); // 1
With Node.js, we can build and use lot of command line apps and utilities which can make us productive and its lot fun to work with them.
Node.js comes up with lot of global objects in global namespace which are available in all modules. Few to name are Console, global, process etc and we would be covering in detail about one such module called Console.
Node.js version comes up with two version one is Console class and another is global console instance which is pre-configured to process.stdout and process.stderr.
Note: Console object is similar javascript console mechanism provided by web browsers. But they are not consistently synchronous like browser APs and at same time they are not asynchronous like node.js streams. They depend on the system I.e. Windows or POSIX. Reference - https://nodejs.org/api/process.html#a-note-on-process-io.
Few of the methods available in console are captured below in browser console window:
Below is an example of global console object which can be used in a node file (index.js in previous examples):
console.log('hello world'); // Prints: hello world, to stdout as we are using the global console console.log('hello %s', 'world'); // Prints: hello world, to stdout with an argument const greeting = 'hello'; console.log(`${greeting} world`); // Prints: hello world, to stdout with an external variable console.warn(`Warning! Invalid format.`); // Prints the warning message in warning color console.info('Info - Logged info successfully.') // Prints the info, similar to log. console.error('Error occured while processing.'); // Print the error with the given error message.
Similar to global console object, we can create the instance of Console class and log the same information. (replace below content in index.js file)
import { stdin, stdout } from 'process'; const myConsole = new console.Console(stdout, stdin); myConsole.log('hello world'); // Prints: hello world, to stdout as we are using the global console myConsole.log('hello %s', 'world'); // Prints: hello world, to stdout with an argument const greeting = 'hello'; myConsole.log(`${greeting} world`); // Prints: hello world, to stdout with a external variable
The global console and the new console instance use the same output i.e., process.stdout and process.stderr. In case if you are wondering why we have two approaches then here is the reason.
The parameters passed to the Console class we have one or two writable stream instances. First argument stdout is used by log or info methods and the second argument stderr is used for warning or error output. And more importantly we can configure the stream to be other stream instance like file system as shown below.
Steps:
import fs from 'fs'; const output = fs.createWriteStream('./stdout.log'); const errorOutput = fs.createWriteStream('./stderr.log'); // Custom simple logger const logger = new console.Console({ stdout: output, stderr: errorOutput }); // use it like console logger.log('hello world'); // it is written to stdout.log file logger.warn('Warning message'); // it is written to stderr.log file
Note: Debug, Info are alias for log method whereas warn is an alias for error method. Internally they use the util.format() for formatting the message.
Method(s): time, timeLog and timeEnd.
Console module is associated with timer to compute the duration of an operation. It exposes the below methods:
Example - Replace the content of index.js with below code and execute node index.js in terminal:
console.time('process'); // starts the timer and associate with label process. const value = 42; // imagine a expensive operation. console.timeLog('process', value); // prints the time elapsed. console.timeEnd('process'); // prints the total time taken from call to time to timeEnd.
Method(s): group, groupCollapsed and groupEnd.
Another set of methods related to indentation are group, groupCollapsed(alias of group) and groupEnd.
Below is a snap in browser console.
Method(s): count
Console maintains an internal counter based on label to count with count method. And for resetting the counter there is another method countReset.
Below is a snap in browser console.
Method(s): dir
To log information to a stdout, we can use log method but to capture the entire object and display an interactive list of properties we can rely on ‘console.dir’.
Below is a snap in browser console.
Method(s): table
Another useful method to display the array of objects in tabular form is ‘console.table’ with an optional argument of properties to be displayed in tabular form.
Below is a snap in browser console.
Building a Custom logger with file stream H2
Custom logger built using file stream:
import util from 'util'; import fs from 'fs'; const output = fs.createWriteStream('./stdout.log'); const errorOutput = fs.createWriteStream('./stderr.log'); // Simple logger const logger = new console.Console({stdout: output, stderr: errorOutput, inspectOptions: { // Maximum number of Array elements to include when formatting. maxArrayLength: 3, // Maximum number of characters to include when formatting. maxStringLength: 10, // If properties of an object are sorted sorted: true, // Remember to enable the color mode. Default is false. colors: true }} ); // display first 10 characters logger.log('log: object', {attr: 'string content a b c d e f g h i j k'}); // log: object { attr: ‘string content a b c’… 16 more characters } // display first 3 items logger.log('log: array', ['array_value1', 'array_value2', 'array_value3', 'array_value4', 'array_value5']); // log: array [ ‘array_value1’, ‘array_value2’, ‘array_value3’, … 2 more items ] // sorted array is displayed logger.log('log: set', new Set([3, 1, 2, 5, 4])); // log: set Set(5) { 1, 2, 3, 4, 5 } // number styling is changed to blue util.inspect.styles.number = 'blue'; // numbers are shown in blue logger.log('log: set', new Set([30, 10, 20, 50, 40])); // log: set Set { 10, 20, 30, 40, 50 }
Output:
All the things one can do with NodeJS
The Console class can be used to create a logger with configurable output streams and for the basic usage we can rely on the global console which has predefined configuration of Process.stdin and process.stderr.
Based on the configurable output stream and the platform, they can be synchronous or asynchronous which helps the processing/logging to be offloaded.
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