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Hello everyone. I am new to web virgin. I can not find information on my question in any way. The meaning of my task is this -when the "ArrowUp" key is pressed, the first part in the input, where the day is displayed, should be highlighted and increased by one 23/10/2021= > 10/24/2021 , while the rest should remain unchanged, and when you click "ArrowDown" vice versa. There are two problems. The first is that when pressed, the number is highlighted and added, but when pressed again, the cursor moves to the beginning and the selection disappears. How do I preserve the state of the selection and prevent the cursor from moving? The second problem is when pressing for example the "ArrowUp" key (add a number), and then "ArrowDown" decrease the number= > the number increases twice, the third press starts decreasing the number. That is, it turns out that when you press to decrease the number, it works the second time. I hope I got it right with the explanation.))

PS : if we remove inputEl.current.selectionStart=== 1, then the selection state is preserved, but I need to catch the cursor position to change the rest of the input.

My Code

import React, {useState, useEffect, useRef} from "react";
import styles from "./DataInput.module.css";
const cur_date= new Date ();
const def_day= cur_date.getDate ();
const def_month= cur_date.getMonth ();
const def_year= cur_date.getFullYear ();
const def_hour= cur_date.getHours ();
const def_minute= cur_date.getMinutes ();
const def_seconds= cur_date.getSeconds ();
/* const months= {
  1: "January",
  2: "February",
  3: "March",
  4: "April",
  5: "May",
  6: "June",
  7: "July",
  8: "August",
  9: "September",
  10: "October",
  11: "November",
  12: "December",
}; * /
const DataInput= ()= >
 {
  const [milisec, setMilisec]= useState (cur_date.valueOf ());
  const [date, setDate]= useState ({
    day: def_day,
    month: def_month,
    year: def_year,
    hour: def_hour,
    minute: def_minute,
    second: def_seconds,
  });
  const {day, month, year, hour, minute, second}= date;
  const date_format= `$ {(" 0 "+ day) .slice (
    -2
  )} /$ {month} /$ {year} $ {hour}: $ {minute}: $ {second} `;
  const inputEl= useRef ();
  const [selection, setSelection]= useState ();
  useEffect (()= >
 {
    if (! selection) return; //prevent running on start
    const {start, end}= selection;
    inputEl.current.focus ();
    inputEl.current.setSelectionRange (start, end);
  },
 [selection]);
  const keyHandler= (e)= >
 {
    console.log (e.code);
    if (e.code=== "ArrowUp" /* &
&
 inputEl.current.selectionStart=== 1 * /) {
      setSelection ({start: 0, end: 2});
      setMilisec ((prevState)= >
 prevState + 86400000);
      setDate ((prevState)= >
 {
        return {... prevState, day: new Date (milisec) .getDate ()};
      });
    }
    if (e.code=== "ArrowDown" /* &
&
 inputEl.current.selectionStart=== 1 * /) {
      setSelection ({start: 0, end: 2});
      setMilisec ((prevState)= >
 prevState -86400000);
      setDate ((prevState)= >
 {
        return {... prevState, day: new Date (milisec) .getDate ()};
      });
    }
  };
  const changeHandler= (e)= >
 {
    return e.target.value;
  };
  return (
    <
div className= {styles.main} >
      <
h1 >
 Frontend Task <
/h1 >
      <
p id= "name" >
Abramov David <
/p >< input
        ref= {inputEl}
        value= {date_format}
        onChange= {changeHandler}
        onKeyDown= {keyHandler}
      />
    <
/div >
  );
};
export default DataInput;
  • Answer # 1
    1. In order to prevent the cursor from moving, you need to inside the functionkeyHandlerto summone.preventDefault ()... In this case, the cursor will not move anywhere when the arrows are pressed
    2. Desynchronization of clicks and actions occurs due to a different way of setting the state insidekeyHandler
      For the first render, let's say the values ​​of the variables are:
    milisec= 1609448400000
    date= {
      day: 1,
      month: 0,
      year: 2021,
      hour: 0,
      minute: 0,
      second: 0,
    }
    

    pressing the up arrow calls

    setMilisec ((prevState)= >
     prevState + 86400000);
    setDate ((prevState)= >
     {
        return {... prevState, day: new Date (milisec) .getDate ()};
    });
    

    if you substitute the values ​​of the variables, then the code will look like this

    setMilisec ((prevState)= >
     1609448400000 + 86400000);
    setDate ((prevState)= >
     {
        return {... prevState, day: new Date (1609448400000) .getDate ()};
    });
    

    thus desynchronization of two values ​​occurs, because milisec is set taking into account its past value, but date is not
    To fix this, you can set the same value inside two function calls like this:

    const keyHandler= (e)= >
     {
      if (e.code=== "ArrowUp" &
    &
     inputEl.current.selectionStart <
     3) {
        e.preventDefault ();
        let nextMilisec= milisec+ 86400000;
        setSelection ({start: 0, end: 2});
        setMilisec (nextMilisec);
        setDate ((prevState)= >
     {
          return {... prevState, day: new Date (nextMilisec) .getDate ()};
        });
      }
      if (e.code=== "ArrowDown" &
    &
     inputEl.current.selectionStart <
     3) {
        e.preventDefault ();
        let nextMilisec= milisec -86400000;
        setSelection ({start: 0, end: 2});
        setMilisec (nextMilisec);
        setDate ((prevState)= >
     {
          return {... prevState, day: new Date (nextMilisec) .getDate ()};
        });
      }
    };
    

    Everything is ingeniously simple, many thanks!)

    David Abramov2021-11-05 18:44:55
  • Answer # 2
    1. In order to prevent the cursor from moving, you need to inside the functionkeyHandlerto summone.preventDefault ()... In this case, the cursor will not move anywhere when the arrows are pressed
    2. Desynchronization of clicks and actions occurs due to a different way of setting the state insidekeyHandler
      For the first render, let's say the values ​​of the variables are:
    milisec= 1609448400000
    date= {
      day: 1,
      month: 0,
      year: 2021,
      hour: 0,
      minute: 0,
      second: 0,
    }
    

    pressing the up arrow calls

    setMilisec ((prevState)= >
     prevState + 86400000);
    setDate ((prevState)= >
     {
        return {... prevState, day: new Date (milisec) .getDate ()};
    });
    

    if you substitute the values ​​of the variables, then the code will look like this

    setMilisec ((prevState)= >
     1609448400000 + 86400000);
    setDate ((prevState)= >
     {
        return {... prevState, day: new Date (1609448400000) .getDate ()};
    });
    

    thus desynchronization of two values ​​occurs, because milisec is set taking into account its past value, but date is not
    To fix this, you can set the same value inside two function calls like this:

    const keyHandler= (e)= >
     {
      if (e.code=== "ArrowUp" &
    &
     inputEl.current.selectionStart <
     3) {
        e.preventDefault ();
        let nextMilisec= milisec+ 86400000;
        setSelection ({start: 0, end: 2});
        setMilisec (nextMilisec);
        setDate ((prevState)= >
     {
          return {... prevState, day: new Date (nextMilisec) .getDate ()};
        });
      }
      if (e.code=== "ArrowDown" &
    &
     inputEl.current.selectionStart <
     3) {
        e.preventDefault ();
        let nextMilisec= milisec -86400000;
        setSelection ({start: 0, end: 2});
        setMilisec (nextMilisec);
        setDate ((prevState)= >
     {
          return {... prevState, day: new Date (nextMilisec) .getDate ()};
        });
      }
    };
    

    Everything is ingeniously simple, many thanks!)

    David Abramov2021-11-05 18:44:55