import React, { Component } from "react";

class Form extends Component {
    state = {
        data:{},
        errors:{}
     }

import Joi from "@hapi/joi";

  doSubmit = () => {
    // call the server
    console.log("Submitted!");
  };

import Form from "./common/form";
// ...

class LoginForm extends Form {

  renderButton(label) {
    return (
      <button disabled={this.validate()} className="btn btn-primary">
        {label}
      </button>
    );
  }

{this.renderButton("Login")}

  import Input from "./input";
  //...

  renderInput(name, label) {
    const { data, errors } = this.state;
    return (
      <Input
        name={name}
        label={label}
        value={data[name]}
        onChange={this.handleChange}
        error={errors[name]}
      />
    );

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        {this.renderInput("username", "Username")}
        {this.renderInput("password", "Password")}
        {this.renderButton("Login")}
      </form>
    );
  }

  renderInput(name, label, type = "text") {
    const { data, errors } = this.state;
    return (
      <Input
        name={name}
        type={type}
        label={label}
        value={data[name]}
        onChange={this.handleChange}
        error={errors[name]}
      />
    );
  }

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        {this.renderInput("username", "Username")}
        {this.renderInput("password", "Password", "password")}
        {this.renderButton("Login")}
      </form>
    );
}

import React from "react";

const Input = ({ name, type, label, value, error, onChange }) => {
  return (
    <div className="form-group">
      <label htmlFor={name}>{label}</label>
      <input
        value={value}
        onChange={onChange}
        id={name}
        name={name}
        type={type}
        className="form-control"
      />
      {error && <div className="alert alert-danger">{error}</div>}
    </div>
  );
};

export default Input;

<input
  value={value}
  name={name}
  type={type}
  onChange={onChange}
  id={name}
  className="form-control"
/>

import React from "react";

const Input = ({ name, label, error, ...rest }) => {
  return (
    <div className="form-group">
      <label htmlFor={name}>{label}</label>
      <input {...rest} name={name} id={name} className="form-control" />
      {error && <div className="alert alert-danger">{error}</div>}
    </div>
  );
};

export default Input;

> create-react-app sample-02
> cd sample-02
> npm start

./src/index.js
  Line 14:15:  'i' is not defined  no-undef

Search for the keywords to learn more about each error.

 const x = 1;
x = 2; // Attempting to override 'x' which is a constant.
 

const person = {
  name: "User 1",
  walk: function() {}, // method
  talk() {} // concise method
};

const person = {
  name: "User 1",
  walk() {},
  talk() {}
};

person.talk();
person.name = "User 3";
person["name"] = "User 2";

const targetMember = "name";
person[targetMember] = "User 2";

const person = {
  name: "User 1",
  walk() {
    console.log(this);
  },
  talk() {}
};

person.walk();

const walk = person.walk;
console.log(walk);

const walk2 = person.walk.bind(person);
console.log(walk2);
walk2();

const square = function(number) {
  return number * number;
};

const square2 = (number) => {
  return number * number;
};

const square2 = number => {
  return number * number;
};

const square3 = number => number * number;
console.log(square3(5));

var activeJobs = jobs.filter(function(job) {
  return job.isActive;
});

var activeJobs2 = jobs.filter(job => job.isActive);

const user = {
  name: "User 1",
  talk() {
    console.log(this);
  }
};
user.talk();

const user = {
  name: "User 1",
  talk() {
    setTimeout(function() {
      console.log(this);
    }, 1000);
  }
};
user.talk();

const user2 = {
  name: "User 2",
  talk() {
    var self = this;
    setTimeout(function() {
      console.log(self);
    }, 1000);
  }
};
user2.talk();

const user3 = {
  name: "User 3",
  talk() {
    setTimeout(() => console.log(this), 1000);
  }
};
user3.talk();

// load the image and convert it to grayscale
var image = new Mat(fileName);
 
if (rotation != 0)
{
    rotateImage(image, image, rotation, 1);
}
 
if (debug)
{
    Cv2.ImShow("Source", image);
    Cv2.WaitKey(1); // do events
}
 
var gray = new Mat();
var channels = image.Channels();
if (channels > 1)
{
    Cv2.CvtColor(image, gray, ColorConversion.BgrToGray);
}
else
{
    image.CopyTo(gray);
}

// compute the Scharr gradient magnitude representation of the images
// in both the x and y direction
var gradX = new Mat();
Cv2.Sobel(gray, gradX, MatType.CV_32F, xorder: 1, yorder: 0, ksize: -1);
//Cv2.Scharr(gray, gradX, MatType.CV_32F, xorder: 1, yorder: 0);
 
var gradY = new Mat();
Cv2.Sobel(gray, gradY, MatType.CV_32F, xorder: 0, yorder: 1, ksize: -1);
//Cv2.Scharr(gray, gradY, MatType.CV_32F, xorder: 0, yorder: 1);
 
// subtract the y-gradient from the x-gradient
var gradient = new Mat();
Cv2.Subtract(gradX, gradY, gradient);
Cv2.ConvertScaleAbs(gradient, gradient);
 
if (debug)
{
    Cv2.ImShow("Gradient", gradient);
    Cv2.WaitKey(1); // do events
}

// blur and threshold the image
var blurred = new Mat();
Cv2.Blur(gradient, blurred, new Size(9, 9));
 
var threshImage = new Mat();
Cv2.Threshold(blurred, threshImage, thresh, 255, ThresholdType.Binary);
 
if (debug)
{
    Cv2.ImShow("Thresh", threshImage);
    Cv2.WaitKey(1); // do events
}
 
 
// construct a closing kernel and apply it to the thresholded image
var kernel = Cv2.GetStructuringElement(StructuringElementShape.Rect, new Size(21, 7));
var closed = new Mat();
Cv2.MorphologyEx(threshImage, closed, MorphologyOperation.Close, kernel);
 
if (debug)
{
    Cv2.ImShow("Closed", closed);
    Cv2.WaitKey(1); // do events
}
 
 
// perform a series of erosions and dilations
Cv2.Erode(closed, closed, null, iterations: 4);
Cv2.Dilate(closed, closed, null, iterations: 4);
 
if (debug)
{
    Cv2.ImShow("Erode & Dilate", closed);
    Cv2.WaitKey(1); // do events
}

//find the contours in the thresholded image, then sort the contours
//by their area, keeping only the largest one
 
Point[][] contours;
HiearchyIndex[] hierarchyIndexes;
Cv2.FindContours(
    closed,
    out contours,
    out hierarchyIndexes,
    mode: ContourRetrieval.CComp,
    method: ContourChain.ApproxSimple);
 
if (contours.Length == 0)
{
    throw new NotSupportedException("Couldn't find any object in the image.");
}
 
var contourIndex = 0;
var previousArea = 0;
var biggestContourRect = Cv2.BoundingRect(contours[0]);
while ((contourIndex >= 0))
{
    var contour = contours[contourIndex];
 
    var boundingRect = Cv2.BoundingRect(contour); //Find bounding rect for each contour
    var boundingRectArea = boundingRect.Width * boundingRect.Height;
    if (boundingRectArea > previousArea)
    {
        biggestContourRect = boundingRect;
        previousArea = boundingRectArea;
    }
 
    contourIndex = hierarchyIndexes[contourIndex].Next;
}
 
 
var barcode = new Mat(image, biggestContourRect); //Crop the image
Cv2.CvtColor(barcode, barcode, ColorConversion.BgrToGray);
 
Cv2.ImShow("Barcode", barcode);
Cv2.WaitKey(1); // do events

 PM> Install-Package ZXing.Net

private static string getBarcodeText(Mat barcode)
{
    // `ZXing.Net` needs a white space around the barcode
    var barcodeWithWhiteSpace = new Mat(new Size(barcode.Width + 30, barcode.Height + 30), MatType.CV_8U, Scalar.White);
    var drawingRect = new Rect(new Point(15, 15), new Size(barcode.Width, barcode.Height));
    var roi = barcodeWithWhiteSpace[drawingRect];
    barcode.CopyTo(roi);
 
    Cv2.ImShow("Enhanced Barcode", barcodeWithWhiteSpace);
    Cv2.WaitKey(1); // do events
 
    return decodeBarcodeText(barcodeWithWhiteSpace.ToBitmap());
}
 
private static string decodeBarcodeText(System.Drawing.Bitmap barcodeBitmap)
{
    var source = new BitmapLuminanceSource(barcodeBitmap);
 
    // using http://zxingnet.codeplex.com/
    // PM> Install-Package ZXing.Net
    var reader = new BarcodeReader(null, null, ls => new GlobalHistogramBinarizer(ls))
    {
        AutoRotate = true,
        TryInverted = true,
        Options = new DecodingOptions
        {
            TryHarder = true,
            //PureBarcode = true,
            /*PossibleFormats = new List<BarcodeFormat>
                    {
                        BarcodeFormat.CODE_128
                        //BarcodeFormat.EAN_8,
                        //BarcodeFormat.CODE_39,
                        //BarcodeFormat.UPC_A
                    }*/
        }
    };
 
    //var newhint = new KeyValuePair<DecodeHintType, object>(DecodeHintType.ALLOWED_EAN_EXTENSIONS, new Object());
    //reader.Options.Hints.Add(newhint);
 
    var result = reader.Decode(source);
    if (result == null)
    {
        Console.WriteLine("Decode failed.");
        return string.Empty;
    }
 
    Console.WriteLine("BarcodeFormat: {0}", result.BarcodeFormat);
    Console.WriteLine("Result: {0}", result.Text);
 
 
    var writer = new BarcodeWriter
    {
        Format = result.BarcodeFormat,
        Options = { Width = 200, Height = 50, Margin = 4},
        Renderer = new ZXing.Rendering.BitmapRenderer()
    };
    var barcodeImage = writer.Write(result.Text);
    Cv2.ImShow("BarcodeWriter", barcodeImage.ToMat());
 
    return result.Text;
}

var barcodeClone = barcode.Clone();
var barcodeText = getBarcodeText(barcodeClone);
 
if (string.IsNullOrWhiteSpace(barcodeText))
{
    Console.WriteLine("Enhancing the barcode...");
    //Cv2.AdaptiveThreshold(barcode, barcode, 255,
        //AdaptiveThresholdType.GaussianC, ThresholdType.Binary, 9, 1);
    //var th = 119;
    var th = 100;
    Cv2.Threshold(barcode, barcode, th, 255, ThresholdType.ToZero);
    Cv2.Threshold(barcode, barcode, th, 255, ThresholdType.Binary);
    barcodeText = getBarcodeText(barcode);
}
 
Cv2.Rectangle(image,
    new Point(biggestContourRect.X, biggestContourRect.Y),
    new Point(biggestContourRect.X + biggestContourRect.Width, biggestContourRect.Y + biggestContourRect.Height),
    new Scalar(0, 255, 0),
    2);
 
if (debug)
{
    Cv2.ImShow("Segmented Source", image);
    Cv2.WaitKey(1); // do events
}
 
Cv2.WaitKey(0);
Cv2.DestroyAllWindows();

// RandomGenerator.cs
using System;
using System.Security.Cryptography;

namespace PersianCaptchaHandler
{
    public class RandomGenerator
    {
        private static readonly byte[] Randb = new byte[4];
        private static readonly RNGCryptoServiceProvider Rand = new RNGCryptoServiceProvider();

        public static int Next()
        {
            Rand.GetBytes(Randb);
            var value = BitConverter.ToInt32(Randb, 0);
            if (value < 0) value = -value;
            return value;
        }
        public static int Next(int max)
        {
            Rand.GetBytes(Randb);
            var value = BitConverter.ToInt32(Randb, 0);
            value = value%(max + 1);
            if (value < 0) value = -value;
            return value;
        }
        public static int Next(int min, int max)
        {
            var value = Next(max - min) + min;
            return value;
        }
    }
}

// NumberToString.cs
namespace PersianCaptchaHandler
{
    public class NumberToString
    {

        #region Fields
        private static readonly string[] Yakan = new[] { "صفر", "یک", "دو", "سه", "چهار", "پنج", "شش", "هفت", "هشت", "نه" };
        private static readonly string[] Dahgan = new[] { "", "", "بیست", "سی", "چهل", "پنجاه", "شصت", "هفتاد", "هشتاد", "نود" };
        private static readonly string[] Dahyek = new [] { "ده", "یازده", "دوازده", "سیزده", "چهارده", "پانزده", "شانزده", "هفده", "هجده", "نوزده" };
        private static readonly string[] Sadgan = new [] { "", "یکصد", "دوصد", "سیصد", "چهارصد", "پانصد", "ششصد", "هفتصد", "هشتصد", "نهصد" };
        private static readonly string[] Basex = new [] { "", "هزار", "میلیون", "میلیارد", "تریلیون" };
        #endregion

        private static string Getnum3(int num3)
        {
            var s = "";
            var d12 = num3 % 100;
            var d3 = num3 / 100;
            if (d3 != 0)
                s = Sadgan[d3] + " و ";
            if ((d12 >= 10) && (d12 <= 19))
            {
                s = s + Dahyek[d12 - 10];
            }
            else
            {
                var d2 = d12 / 10;
                if (d2 != 0)
                    s = s + Dahgan[d2] + " و ";
                var d1 = d12 % 10;
                if (d1 != 0)
                    s = s + Yakan[d1] + " و ";
                s = s.Substring(0, s.Length - 3);
            }
            return s;
        }

        public static string ConvertIntNumberToFarsiAlphabatic(string snum)
        {
            var stotal = "";
            if (snum == "0") return Yakan[0];

            snum = snum.PadLeft(((snum.Length - 1) / 3 + 1) * 3, '0');
            var l = snum.Length / 3 - 1;
            for (var i = 0; i <= l; i++)
            {
                var b = int.Parse(snum.Substring(i * 3, 3));
                if (b != 0)
                    stotal = stotal + Getnum3(b) + " " + Basex[l - i] + " و ";
            }
            stotal = stotal.Substring(0, stotal.Length - 3);
            return stotal;
        }
    }
}

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace PersianCaptchaHandler
{
    public class Encryptor
    {
        #region constraints
        private static string Password { get { return "Mehdi"; } }
        private static string Salt { get { return "Payervand"; } }
        #endregion

        public static string Encrypt(string clearText)
        {
            // Turn text to bytes
            var clearBytes = Encoding.Unicode.GetBytes(clearText);

            var pdb = new PasswordDeriveBytes(Password, Encoding.Unicode.GetBytes(Salt));

            var ms = new MemoryStream();
            var alg = Rijndael.Create();

            alg.Key = pdb.GetBytes(32);
            alg.IV = pdb.GetBytes(16);

            var cs = new CryptoStream(ms, alg.CreateEncryptor(), CryptoStreamMode.Write);

            cs.Write(clearBytes, 0, clearBytes.Length);
            cs.Close();

            var encryptedData = ms.ToArray();

            return Convert.ToBase64String(encryptedData);
        }
        public static string Decrypt(string cipherText)
        {
            // Convert text to byte
            var cipherBytes = Convert.FromBase64String(cipherText);

            var pdb = new PasswordDeriveBytes(Password, Encoding.Unicode.GetBytes(Salt));

            var ms = new MemoryStream();
            var alg = Rijndael.Create();

            alg.Key = pdb.GetBytes(32);
            alg.IV = pdb.GetBytes(16);

            var cs = new CryptoStream(ms, alg.CreateDecryptor(), CryptoStreamMode.Write);

            cs.Write(cipherBytes, 0, cipherBytes.Length);
            cs.Close();

            var decryptedData = ms.ToArray();

            return Encoding.Unicode.GetString(decryptedData);
        }
    }
}

// Utils.cs
using System.Text.RegularExpressions;

namespace PersianCaptchaHandler
{
    public class Utils
    {
        private static readonly Regex NumberMatch = new Regex(@"^([0-9]*|\d*\.\d{1}?\d*)$", RegexOptions.Compiled);
        public static bool IsNumber(string number2Match)
        {
            return NumberMatch.IsMatch(number2Match);
        }
    }
}

<add verb="GET" path="/captcha/" type="PersianCaptchaHandler.CaptchaHandler, PersianCaptchaHandler, Version=1.0.0.0, Culture=neutral"  />

<!-- ASPX -->
<dl>
    <dt>تصویر امنیتی</dt>
    <dd>
        <asp:Image ID="imgCaptchaText" runat="server" AlternateText="CaptchaImage" />
        <asp:HiddenField ID="hfCaptchaText" runat="server" />
        <asp:ImageButton ID="btnRefreshCaptcha" runat="server" ImageUrl="/img/refresh.png"
            OnClick="btnRefreshCaptcha_Click" />
        <br />
        <asp:TextBox ID="txtCaptcha" runat="server" AutoCompleteType="Disabled"></asp:TextBox>
    </dd>
    <dd>
        <asp:Button ID="btnSubmit" runat="server" Text="ثبت" OnClick="btnSubmit_Click" />
    </dd>
</dl>
<asp:Label ID="lblMessage" runat="server"></asp:Label>

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
                SetCaptcha();
        }

        private void SetCaptcha()
        {
            lblMessage.Text =
            txtCaptcha.Text = string.Empty;

            var newNumber =
                RandomGenerator.Next(100, 999)
                ;

            var farsiAlphabatic = NumberToString.ConvertIntNumberToFarsiAlphabatic(newNumber.ToString());

            hfCaptchaText.Value =
                HttpUtility
                .UrlEncode(
                    Encryptor.Encrypt(
                        farsiAlphabatic
                    )
                );

            txtCaptcha.Text = string.Empty;
            imgCaptchaText.ImageUrl =
                "/captcha/?text=" + hfCaptchaText.Value;
        }

        private string GetCaptcha()
        {
            var farsiAlphabatic = NumberToString.ConvertIntNumberToFarsiAlphabatic(txtCaptcha.Text);

            var encryptedString =
                HttpUtility
                .UrlEncode(
                    Encryptor.Encrypt(
                        farsiAlphabatic
                    )
                );

            return encryptedString;
        }

        private bool ValidateUserInputForLogin()
        {
            if (!Utils.IsNumber(txtCaptcha.Text))
            {
                lblMessage.Text = "تصویر امنیتی را بطور صحیح وارد نکرده اید";
                return false;
            }

            var strGetCaptcha =
                GetCaptcha();

            var strDecodedVAlue =
                hfCaptchaText.Value;

            if (strDecodedVAlue != strGetCaptcha)
            {
                lblMessage.Text = "کلمه امنیتی اشتباه است";
                SetCaptcha();
                return false;
            }
            return true;
        }

        protected void btnSubmit_Click(object sender, EventArgs e)
        {
            if (!ValidateUserInputForLogin()) return;
            lblMessage.Text = "کلمه امنیتی درست است";
        }

        protected void btnRefreshCaptcha_Click(object sender, ImageClickEventArgs e)
        {
            SetCaptcha();
        }

import React, { useState } from "react";

export const Input = () => {
  const [name, setName] = useState("");
  return <input value={name} onChange={(e) => setName(e.target.value)} />;
};

const [name, setName] = useState(0);

const [name, setName] = useState<string>("");

const [name, setName] = useState("");

const [name, setName] = useState<string | null>(null);

import React, { useRef, useState } from "react";

export const Input = () => {
  const [name, setName] = useState("");
  const inputRef = useRef(null);

  if (inputRef && inputRef.current) {
    console.log("ref", inputRef.current.value);
  }
  return (
    <input
      ref={inputRef}
      value={name}
      onChange={(e) => setName(e.target.value)}
    />
  );
};

interface MutableRefObject<T> {
   current: T;
}

const inputRef = useRef<HTMLInputElement>(null);

//if (inputRef && inputRef.current) {
  console.log("ref", inputRef.current.value);
//}

console.log("ref", inputRef?.current?.value);

 PM> Install-Package OpenCvSharp-AnyCPU

 PM> Install-Package OpenCvSharp-WithoutDll

using OpenCvSharp;
 
namespace OpenCVSharpSample01
{
    class Program
    {
        static void Main(string[] args)
        {
            var img = Cv.CreateImage(new CvSize(128, 128), BitDepth.U8, 1);
 
            for (var y = 0; y < img.Height; y++)
            {
                for (var x = 0; x < img.Width; x++)
                {
                    Cv.Set2D(img, y, x, x + y);
                }
            }
 
            Cv.NamedWindow("window");
            Cv.ShowImage("window", img);
            Cv.WaitKey();
            Cv.DestroyWindow("window");
 
            Cv.ReleaseImage(img);
        }
    }
}