React hooks useState Array

Question

I tried looking for resetting useState array values in here but could not find any references to array values.

Trying to change the drop down value from ini

Answer 1

use state is not always needed you can just simply do this

let paymentList = [
    {"id":249,"txnid":"2","fname":"Rigoberto"}, {"id":249,"txnid":"33","fname":"manuel"},]

then use your data in a map loop like this in my case it was just a table and im sure many of you are looking for the same. here is how you use it.

<div className="card-body">
            <div className="table-responsive">
                <table className="table table-striped">
                    <thead>
                        <tr>
                            <th>Transaction ID</th>
                            <th>Name</th>
                        </tr>
                    </thead>
                    <tbody>
                        {
                            paymentList.map((payment, key) => (
                                <tr key={key}>
                                    <td>{payment.txnid}</td>
                                    <td>{payment.fname}</td>
                                </tr>
                            ))
                        }
                    </tbody>
                </table>
            </div>
        </div>

Answer 2

Try to keep your state minimal. There is no need to store

   const initialValue = [
    { id: 0,value: " --- Select a State ---" }];

as state. Separate the permanent from the changing

const ALL_STATE_VALS = [
    { id: 0,value: " --- Select a State ---" }
    { id: 1, value: "Alabama" },
    { id: 2, value: "Georgia" },
    { id: 3, value: "Tennessee" }
];

Then you can store just the id as your state:

const StateSelector = () =>{
  const [selectedStateOption, setselectedStateOption] = useState(0);

  return (
    <div>
      <label>Select a State:</label>
      <select>
        {ALL_STATE_VALS.map((option, index) => (
          <option key={option.id} selected={index===selectedStateOption}>{option.value}</option>
        ))}
      </select>
    </div>);
   )
}

Answer 3

The accepted answer shows the correct way to setState but it does not lead to a well functioning select box.

import React, { useState } from "react"; 
import ReactDOM from "react-dom";

const initialValue = { id: 0,value: " --- Select a State ---" };

const options = [
    { id: 1, value: "Alabama" },
    { id: 2, value: "Georgia" },
    { id: 3, value: "Tennessee" }
];

const StateSelector = () => {   
   const [ selected, setSelected ] = useState(initialValue);  

     return (
       <div>
          <label>Select a State:</label>
          <select value={selected}>
            {selected === initialValue && 
                <option disabled value={initialValue}>{initialValue.value}</option>}
            {options.map((localState, index) => (
               <option key={localState.id} value={localState}>
                   {localState.value}
               </option>
             ))}
          </select>
        </div>
      ); 
};

const rootElement = document.getElementById("root");
ReactDOM.render(<StateSelector />, rootElement);

Answer 4

To expand on Ryan's answer:

Whenever setStateValues is called, React re-renders your component, which means that the function body of the StateSelector component function gets re-executed.

React docs:

setState() will always lead to a re-render unless shouldComponentUpdate() returns false.

Essentially, you're setting state with:

setStateValues(allowedState);

causing a re-render, which then causes the function to execute, and so on. Hence, the loop issue.

To illustrate the point, if you set a timeout as like:

  setTimeout(
    () => setStateValues(allowedState),
    1000
  )

Which ends the 'too many re-renders' issue.

In your case, you're dealing with a side-effect, which is handled with UseEffectin your component functions. You can read more about it here.

Answer 5

You should not set state (or do anything else with side effects) from within the rendering function. When using hooks, you can use useEffect for this.

The following version works:

import React, { useState, useEffect } from "react";
import ReactDOM from "react-dom";

const StateSelector = () => {
  const initialValue = [
    { id: 0, value: " --- Select a State ---" }];

  const allowedState = [
    { id: 1, value: "Alabama" },
    { id: 2, value: "Georgia" },
    { id: 3, value: "Tennessee" }
  ];

  const [stateOptions, setStateValues] = useState(initialValue);
  // initialValue.push(...allowedState);

  console.log(initialValue.length);
  // ****** BEGINNING OF CHANGE ******
  useEffect(() => {
    // Should not ever set state during rendering, so do this in useEffect instead.
    setStateValues(allowedState);
  }, []);
  // ****** END OF CHANGE ******

  return (<div>
    <label>Select a State:</label>
    <select>
      {stateOptions.map((localState, index) => (
        <option key={localState.id}>{localState.value}</option>
      ))}
    </select>
  </div>);
};

const rootElement = document.getElementById("root");
ReactDOM.render(<StateSelector />, rootElement);

and here it is in a code sandbox.

I'm assuming that you want to eventually load the list of states from some dynamic source (otherwise you could just use allowedState directly without using useState at all). If so, that api call to load the list could also go inside the useEffect block.