reactJS and dynamic render with map function my data is repeating

Question

I am starting on an application which needs to dynamically generate input boxes based on a selection from a drop down. This is my code:

import React, { Component } from "react";
import "./App.css";
import { Container, Row, Col, Input, Button, Fa, Card, CardBody } from "mdbreact";

class App extends Component {
  constructor(props) {
    super(props);
    this.state = {
      numberOfUnits: 0,
      name: {
        valid: true,
        value: "",
        label: "Property Nickname",
        length: 0,
        css: "grey-text"
      },
      address: {
        valid: true,
        value: "",
        label: "Property Address",
        length: 0,
        css: "grey-text"
      },
      city: {
        valid: true,
        value: "",
        label: "Property City",
        length: 0,
        css: "grey-text"
      },
      numberOfUnits: {
        valid: true,
        value: "",
        label: "Property City",
        length: 0,
        css: "grey-text"
      }
    };

    this.saveData = this.saveData.bind(this);
    this.setUnitNumber = this.setUnitNumber.bind(this);
  }

  setUnitNumber() {
    let currentComponent = this;

    var localUnitCount = document.getElementById("inputNumberOfUnits").value;
    currentComponent.setState({ numberOfUnits: localUnitCount });
  }

  saveData() {
    let currentComponent = this;

    var validData = true;
    var localName = {
      valid: true,
      value: "",
      label: "Property Nickname",
      length: 0,
      css: "grey-text"
    };
    var localAddress = {
      valid: true,
      value: "",
      label: "Property Nickname",
      length: 0,
      css: "grey-text"
    };
    var localCity = {
      valid: true,
      value: "",
      label: "Property City",
      length: 0,
      css: "grey-text"
    };

    // validate the property nickname
    localName.value = document.getElementById("lblName").value;
    localName.length = localName.value.length;

    if (localName.length < 5) {
      validData = false;
      localName.valid = false;
      localName.label =
        "You did not enter a property nickname (minimum of 5 charaters)";
      localName.css = "text-danger";
    }

    // validate the property address
    localAddress.value = document.getElementById("lblAddress").value;
    localAddress.length = localAddress.value.length;

    if (localAddress.length < 3) {
      validData = false;
      localAddress.valid = false;
      localAddress.label =
        "You did not enter a property Address (minimum of 5 characters)";
      localAddress.css = "text-danger";
    }

    // validate the property city
    localCity.value = document.getElementById("lblCity").value;
    localCity.length = localCity.value.length;

    if (localCity.length < 3) {
      validData = false;
      localCity.valid = false;
      localCity.label =
        "You did not enter a property city (minimum of 3 characters)";
      localCity.css = "text-danger";
    }

    currentComponent.setState({
      name: localName,
      city: localCity,
      address: localAddress
    });
  }

  renderData = () => {
    let currentComponent = this;

    var localUnitCount = this.state.numberOfUnits;
    var idArray = [];
    var idObject = {
      counter: 0,
      idName: ""
    };

    for (var counter = 0; counter < localUnitCount; counter++) {
      var unitName = "Unit";
      if (counter < 10) {
        unitName = unitName + "0";
      }
      unitName = unitName + (counter + 1);
      idObject.counter = counter + 1;
      idObject.idName = unitName;
      idArray[counter] = idObject;
      console.log("idArray[counter]: ", idArray[counter]);
    }

    console.log(idArray);

    return idArray.map(item => (
      <div>
        <div className="oldscanFont">
          <label> Unit {item.counter} </label>
        </div>
        <hr />
      </div>
    ));
  };

  render() {
    return (
      <div className="App">
        <div className="d-flex flex-wrap justify-content-center position-absolute w-100 h-50 align-items-center align-content-center">
          <Container>
            <Row>
              <Col md="6">
                <Card>
                  <CardBody>
                    <form>
                      <p className="h4 text-center py-4">Sign up</p>
                      <div className={this.state.name.css}>
                        <Input
                          id="lblName"
                          label={this.state.name.label}
                          group
                          type="text"
                        />
                      </div>
                      <div className={this.state.address.css}>
                        <Input
                          id="lblAddress"
                          label={this.state.address.label}
                          group
                          type="text"
                        />
                      </div>
                      <div className={this.state.city.css}>
                        <Input
                          id="lblCity"
                          label={this.state.city.label}
                          group
                          type="text"
                        />
                      </div>
                      <div className={this.state.numberOfUnits.css}>
                        <div class="input-group mb-3">
                          <div class="input-group-prepend">
                            <label
                              class="input-group-text"
                              for="inputNumberOfUnits"
                            >
                              Number of Units
                            </label>
                          </div>
                          <select
                            class="custom-select"
                            id="inputNumberOfUnits"
                            onChange={() => {
                              this.setUnitNumber();
                            }}
                          >
                            <option value="1" selected>
                              One
                            </option>
                            <option value="2">Two</option>
                            <option value="3">Three</option>
                            <option value="4">Four</option>
                            <option value="5">Five</option>
                            <option value="6">Six</option>
                            <option value="7">Seven</option>
                            <option value="8">Eight</option>
                            <option value="9">Nine</option>
                            <option value="10">Ten</option>
                            <option value="11">Eleven</option>
                            <option value="12">Twelve</option>
                            <option value="13">Thirteen</option>
                            <option value="14">Fourteen</option>
                            <option value="15">Fifteen</option>
                            <option value="16">Sixteen</option>
                            <option value="17">Seventeen</option>
                            <option value="18">Eighteen</option>
                            <option value="19">Nineteen</option>
                            <option value="20">Twenty</option>
                          </select>
                        </div>
                      </div>
                      <div>{this.renderData()}</div>
                      <div className="text-center py-4 mt-3">
                        <Button
                          color="cyan"
                          onClick={() => {
                            this.saveData();
                          }}
                        >
                          Save
                        </Button>
                      </div>
                    </form>
                  </CardBody>
                </Card>
              </Col>
            </Row>
          </Container>
        </div>
      </div>
    );
  }
}

export default App;

When i run the code, and select 4 from the drop down, the application should dynamically generate 4 elements. The code is not complete but for some reason, when I am building the array that gets sent to the map function, the array contains the same data in each instance. Below is a screen shot of the application and the console.log after I selected 4 from the drop down:

As you can see from the console.log, it appears that the idArray is being build correctly but the final console.log shows all 4 instances of the idArray containing the same counter and idName values. Then, when the render executes and I put out {item.counter}, each element contains the same value.

Any idea why this may be happening?

Thank you.

Answer 1

I find this part of renderData method rather interesting.

...
for (var counter = 0; counter < localUnitCount; counter++) {
  var unitName = "Unit";
  if (counter < 10) {
    unitName = unitName + "0";
  }
  unitName = unitName + (counter + 1);
  idObject.counter = counter + 1;
  idObject.idName = unitName;
  idArray[counter] = idObject;
  console.log("idArray[counter]: ", idArray[counter]);
}

idObject is being modified in place instead of as a copy.

This can be written as.

... 
var idNamePrefix = "Unit";
for (var counter = 0, unitName; counter < localUnitCount; counter++) {

  if (counter < 10) {
    unitName = idNamePrefix + "0";
  } else {
    unitName = idNamePrefix + (counter + 1);
  }

  idArray.push(
    // make object with idObject key-values applied.
    // more importantly, the last object replaces the count and idName value.
    Object.assign({}, idObject, {counter: counter + 1, idName: unitName})
  )
}