Debugging http Node.js server requests and responses from shell

Here is a cool tip to inspect Node.js running an http process / server. First off, we start a simple http server in Node.js like this:

const http = require('http');

const server = http.createServer((req, res) => {
    res.end("
Why hello world!
\n");
});

server.listen(4242, () => {
    console.log("Server is running...");
});

This sets up a http server in Node.js. The http module is built-in in Node.js, we only have to require it (import in ES6). Now, just enter the following (I use Windows Subsystem for Linux - WSL in this case) in your shell to export NODE_DEBUG environment variable: export NODE_DEBUG=http We can now see requests and responses in our Node.js server! (Image below uses Wsl-Terminal as our terminal against WSL).

Canceling Promise in Javascript

Canceling Promise in Js is a often sough after functionality, that can be provided by wrapping the Promise async function and provide canceling abilities. This will in functionality be similar to what we can do in C# with a CancellationTokenSource using in System.Threading.Task objects. We can invoke asynchronous function in Js with Promise, but if the user navigates away from a View or Page in for example React Native component, clicking a button to go to another Component, we must tidy up already started Promise operations such as fetch and here is the code to achieve that. First off, we define and export a makeCancelable method to be able to cancel a Promise.

/**
 * Wraps a promise into a cancelable promise, allowing it to be canceled. Useful in scenarios such as navigating away from a view or page and a fetch is already started.
 * @param {Promise}   promise           Promise object to cancel.
 * @return {Object with wrapped promise and a cancel function}
 */
export const makeCancelable = (promise) => {
    let hasCanceled = false;

    const wrappedPromise = new Promise((resolve, reject) => {
        promise.then(value => hasCanceled ? reject({ isCanceled: true }) : resolve(value),
            error => hasCanceled ? reject({ isCanceled: true }) : reject(error)
        );
    });

    return {
        promise: wrappedPromise,
        cancel() {
            hasCanceled: true;
        }
    };

};

The promise is wrapped with additional logic to check a boolean flag in a variable hasCanceled that either rejects the Promise if it is canceled or resolves the Promise (fullfils the async operation). Returned is an object in Js with the Promise itself in a primise attribute and the function cancel() which sets the boolean flag hasCanceled to true, effectively rejecting the Promise and rejecting it. Example usage below:

'use strict';

import React, { Component } from 'react';
import { TextInput, Text, View, StyleSheet, Image, TouchableHighlight, ActivityIndicator, FlatList, AsyncStorage } from 'react-native';
import AuthService from './AuthService';
import { makeCancelable } from './Util';

const styles = StyleSheet.create({
    container: {
        backgroundColor: '#F5FCFF',
        flex: 1,
        paddingTop: 40,
        alignItems: 'center'
    },
    heading: {
        fontSize: 30,
        fontWeight: '100',
        marginTop: 20
    },
    input: {
        height: 50,
        marginTop: 10,
        padding: 4,
        margin: 2,
        alignSelf: 'stretch',
        fontSize: 18,
        borderWidth: 1,
        borderColor: '#48bbec'
    },
    button: {
        height: 50,
        backgroundColor: '#48bbec',
        alignSelf: 'stretch',
        marginTop: 10,
        justifyContent: 'center'
    },
    buttonText: {
        fontSize: 22,
        color: '#FFF',
        alignSelf: 'center'
    },
    error: {
        fontWeight: '300',
        fontSize: 20,
        color: 'red',
        paddingTop: 10
    }
});

const cancelableSearchRepositoriesPromiseFetch = makeCancelable(fetch('https://api.github.com/search/repositories?q=react'));

class LoginForm extends Component {

    constructor(props) {
        super(props);

        this.state = {
            showProgress: false,
            username: '',
            password: '',
            repos: [],
            badCredentials: false,
            unknownError: false,
        };


    }

    onLoginPressed() {
        this.setState({ showProgress: true });

        var reposFound = [];

        var authService = new AuthService();

        authService.login({
            username: this.state.username, password: this.state.password
        }, (results) => {
            this.setState(Object.assign({ showProgress: false }, results));

            if (this.state.success && this.props.onLogin) {
                this.props.onLogin();
            }

        });




        cancelableSearchRepositoriesPromiseFetch.promise.then((response) => { return response.json(); })
            .then((results) => {
                results.items.forEach(item => {
                    reposFound.push(item);
                });
                this.setState({ repos: reposFound, showProgress: false });
            });
    }

    componentWillMount() {
        this._retrieveLastCredentials();
        cancelableSearchRepositoriesPromiseFetch.cancel();
    }

    _retrieveLastCredentials = async () => {

        var lastusername = await AsyncStorage.getItem("GithubDemo:LastUsername");
        var lastpassword = await AsyncStorage.getItem("GithubDemo:LastPassword");
        this.setState({ username: lastusername, password: lastpassword });
    }

    _saveLastUsername = async (username) => {
        if (username != null) {
            await AsyncStorage.setItem("GithubDemo:LastUsername", username);
        }
    }

    _savePassword = async (password) => {
        if (password != null) {
            await AsyncStorage.setItem("GithubDemo:LastPassword", password);
        }
    }

    componentWillUnmount() {

    }

    render() {


        var errorCtrl = <View />;

        if (!this.state.success && this.state.badCredentials) {
            errorCtrl = <Text color='#FF0000' style={styles.error}>That username and password combination did not work</Text>
        }

        if (!this.state.success && this.state.unknownError) {
            errorCtrl = <Text color='#FF0000' style={styles.error}>Unexpected error while logging in. Try again later</Text>
        }

        return (
            <View style={styles.container}>
                <Image style={{ width: 66, height: 55 }} source={require('./assets/Octocat.png')} />
                <Text style={styles.heading}>Github browser</Text>
                <TextInput value={this.state.username} onChangeText={(text) => { this._saveLastUsername(text); this.setState({ username: text }); }} style={styles.input} placeholder='Github username' />
                <TextInput value={this.state.password} textContentType={'password'} multiline={false} secureTextEntry={true} onChangeText={(text) => { this._savePassword(text); this.setState({ password: text }); }} style={styles.input} placeholder='Github password' />
                <TouchableHighlight style={styles.button} onPress={this.onLoginPressed.bind(this)}>
                    <Text style={styles.buttonText}>Log in</Text>
                </TouchableHighlight>
                {errorCtrl}
                <ActivityIndicator animating={this.state.showProgress} size={"large"} />
                <FlatList keyExtractor={item => item.id} data={this.state.repos} renderItem={({ item }) => <Text>{item.full_name}</Text>} />

            </View>
        );

    }


}

export default LoginForm; 

React native - Checkboxes and date pickers for IoS

This article will look at checkboxes and date pickers for IoS apps in React Native. For checkboxes, we use the built-in Switch control. For Date pickers we use the built-in DatePickerIOS control.

This is the basic JS / JSX to get you started! Note the use of a basic state variable to keep track of the chosenDate. The onDateChange callback uses an arrow inline function to update the state variable. We also set the minimum and maximum datetime allowed and some othern nice props of the control! App.js

import React from 'react';
import { StyleSheet, Text, View, DatePickerIOS, Switch } from 'react-native';

export default class App extends React.Component {

  constructor(props){
    super(props);
    this.state = { chosenDate : new Date(), isDatePickerVisible: false };

    this.setDate = this.setDate.bind(this);
  }

  setDate(newDate){
    this.setState({chosenDate: newDate })
  }


  render() {
    return (
      <View style={styles.container}>
 
        <Switch onValueChange={(val) => this.setState({ isDatePickerVisible : val })} value={this.state.isDatePickerVisible} ios_backgroundColor={"aliceblue"} trackColor={true} />
        <Text style={{ display: this.state.isDatePickerVisible ? "none" : "flex"}}>Choose datetime..</Text>
          
        <View style={{ display: this.state.isDatePickerVisible ? "flex" : "none" }}>
         <DatePickerIOS locale="no" mode={"datetime"} minuteInterval={10} minimumDate={new Date(2018,11,1)} maximumDate={new Date(2018,11,31)}
          style={{ borderWidth: 1, borderColor: 'gray'}} onDateChange={this.setDate} date={this.state.chosenDate} />
         <Text>{this.state.chosenDate.toLocaleDateString() + " " + this.state.chosenDate.toLocaleTimeString()}</Text>
        </View>
  
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
  },
});