rogerxu
commented
7 years ago Basic
How to exit from a Node.js program
process.exit
process.on('exit', function () {
});
process.exit();
process.exit(1);You need to send the command a SIGTERM singal, and handle that with the process signal hander.
const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.send('hi');
});
const server = app.listen(30000, () => console.log('Server ready'));
process.on('SIGTERM', () => {
server.close(() => {
console.log('Process terminated');
});
});SIGTERM is the signals that tells a process to gracefully terminate. It is the signal that's sent from process managers like upstart or supervisord and many others.
You can send this signal from inside the program, in another function:
process.kill(process.pid, 'SIGTERM');How to read environment variables
The process core module of Node provides the env property which hosts all the environment variables that were set at the moment the process was started.
process.env.NODE_ENV // 'production'Command Line
Pass arguments from the command line
node app.js name=rogerprocess.argv - Array
The first argument is the full path of the node command.
The second element is the full path of the file being executed.
All the additional argumetns are present from the third position going forward.
const args = process.argv.slice(2);
args[0] // name=rogerThe best way to parse it is by using the minimist package.
const minimist = require('minimist');
const args = minimist(process.argv.slice(2));
args['name'] // rogerOutput to the command line
console.log()
console.log('My %s has %d years', 'cat', 2);console.count()
console.count(msg);Print the stack trace
const foo = () => console.trace();
const bar = () => foo();
bar();Calculate the time spent
const doSomething = () => console.log('test');
const measure = () => {
console.time('doSomething');
doSomething();
console.timeEnd('doSomething');
};
measure();Standard input and output
process.stdout
process.stdout.write('hello world');process.stdin
process.stdin.on('data', function (data) {
console.log(data.toString().trim());
});Color the output
You can color the output of your text in the console by using escape sequences.
console.log('\x1b[33m%s\x1b[0m', 'hi!');chalk package
const chalk = require('chalk');
console.log(chalk.yellow('hi!'));Create a progress bar
progress package
const ProgressBar = require('progress');
const bar = new ProgressBar(':bar', {
total: 10,
});
const timer = setInterval(() => {
bar.tick();
if (bar.complete) {
clearInterval(timer);
}
}, 100);Accept input from the command line
Node readline module.
const readline = require('readline');
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout,
});
rl.question('What is your name?', (name) => {
console.log(`Hi ${name}!`);
rl.close();
});const readline = require('readline');
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout,
});
rl.question('What is your name? ', (answer) => {
person.name = answer;
rl.setPrompt(`What would ${person.name} say? `);
rl.prompt(); // write a new line
rl.on('line', (saying) => {
person.sayings.push(saying.trim());
if (saying.toLowerCase().trim() === 'exit') {
rl.close();
} else {
rl.setPrompt(`What else would ${person.name} say? ('exit' to leave) `);
rl.prompt();
}
});
});
rl.on('close', () => {
process.exit();
});inquirer package
cosnt inquirer = require('inquirer');
const questions = [{
type: 'input',
name: 'name',
message: 'What is your name?',
}];
inquirer.prompt(questions).then(answers => {
console.log(`Hi ${answers['name']}!`);
});Node Core
The global object
global- The global namespace object.__dirname- The directory name of the current module.__filename- The file name of the current module.
const path = require('path');
path.basename(__filename); // abc.jsGlobal timing functions
setTimeoutclearTimeoutsetIntervalclearInterval
function writeWaitingPercent(percent) {
process.stdout.clearLine();
process.stdout.cursorTo(0);
process.stdout.write(`waiting ... ${percent}%`);
}
var interval = setInterval(function () {
currentTime += waitInterval;
percentWaited = Math.floor((currentTime / waitTime) * 100);
writeWaitingPercent(percentWaited);
}, waitInterval);
setTimeout(function () {
clearInterval(interval);
writeWaitingPercent(100);
console.log('\n\ndone');
}, waitTime);exec
const exec = require('child_process').exec;
exec('git version', function(err, stdout) {
if (err) {
throw err;
}
console.log('Git Version Executed');
console.log(stdout);
});spawn
const spawn = require('child_process').spawn;
const cp = spawn('node', ['--version']);
cp.stdout.on('data', function (data) {
console.log(`STDOUT: ${data.toString()}`);
});
cp.on('close', function () {
console.log('Child process has ended');
process.exit();
});
maxogden/art-of-node: a short introduction to node.js
Tutorials
NodeSchool
Best Practices
goldbergyoni/nodebestpractices: The Node.js best practices list (March 2020)
19 things I learnt reading the NodeJS docs – Hacker Noon