React Js, adding new object to an array [duplicate]

Question

I have a text field and a radio button.

I am making an object of these two values and putting inside an array, so that i can store this in Mongo DB.

I am constructing an array of objects and trying to iterate for showing the details in a table.

Not able to displaying the details.

Help needed for this.

 export class AddColumns extends React.Component{

  constructor(props) {
      super(props);
        this.state={
            newItemInput: '',
            selectedValue: '',
            buyItems :[],
            object : {}
        }
      }

  handleChange=(event)=> {
    this.setState({
      ...this.state,
      selectedValue: event.target.value
    });
  };

  change (event){
    this.setState({
      [event.target.name]:event.target.value
    });
  };

addItem(e){
    e.preventDefault();

    const newItemInput = this.state.newItemInput;
    const newRadioValue = this.state.selectedValue;
    const obj = {'item':newItemInput, 'columnType':newRadioValue};
    this.state.buyItems.push(obj);
    console.log(this.state.buyItems);       
  }

  render(){
    const {buyItems,message} = this.state;
    return (
      <div className="container">
          <form className="form-inline" onSubmit={(e) => {this.addItem(e)}}>
            <div className="form-group">
              <label className="sr-only" htmlFor="newItemInput">Add New Item</label>
              <input type ="text" ref ={input => this.newColumn = input} name="newItemInput" placeholder="Modules" value = {this.state.newItemInput} className="form-control" 
                      id="newItemInput" onChange={event => this.change(event)}/>
            </div>

            <div className="k-form-field">
              <input type="radio" name="radio" value="radio1" className="k-radio" onChange={this.handleChange}/>
              <label className="k-radio-label">RadioButton 1</label>

              <input type="radio" name="radio" value="radio2" className="k-radio" onChange={this.handleChange}/>
              <label className="k-radio-label">RadioButton 2</label>

            <div className="form-group">
              <button type="submit" className="btn btn-primary">Add</button><p>{this.state.messgae}</p>
            </div>
          </form>
        <div className="content">
          <div>
                  {
                    buyItems.map((rowdata,i) => { 
                        <div>
                          {rowdata.item}
                        </div>
                    })
                  }
            </div>      
        </div>
      </div>
      );
  }
}

Answer 1

For the view to update, you must call setState, and not just push an item to the array, you can easily do it using the spread syntax:

addItem(e){
    e.preventDefault();
    const newItemInput = this.state.newItemInput;
    const newRadioValue = this.state.selectedValue;
    const obj = {'item':newItemInput, 'columnType':newRadioValue};
    this.setState({
        buyItems: [...this.state.buyItems, obj]
    });
    console.log(this.state.buyItems);       
}

An alternative would be create a copy of the old array, push the new item and proceed to set the state:

addItem(e){
    e.preventDefault();
    const newItemInput = this.state.newItemInput;
    const newRadioValue = this.state.selectedValue;
    const obj = {'item':newItemInput, 'columnType':newRadioValue};
    const newArray = this.state.buyItems.slice(); // Create a copy
    newArray.push(obj); // Push the object
    this.setState({ buyItems: newArray });
    console.log(this.state.buyItems);       
}