how to read this.props in a function

Question

I'm new to reactjs with ES6, the problem is that I can not read the 'this.props.productId' property inside the onDelete () function, this is the error: DeleteProductComponent.js:15 Uncaught TypeError: Cannot read property 'props' of null can anyone give me an optimum solution or tell me what I'm doing wrong? Thank you

 import React, { Component } from 'react';

    class DeleteProductComponent extends Component {

     componentDidMount() {

        $('.page-header h1').text('Delete Product');

        }

onDelete(){

var id = this.props.productId;

        $.ajax({
            url: "http://localhost/my-app/public/delete.php",
            type : "POST",
            contentType : 'application/json',
            data : JSON.stringify({'id' : id}),
            success : function(response) {
                this.props.changeAppMode('read');
            }.bind(this),
            error: function(xhr, resp, text){
                // show error in console
                console.log(xhr, resp, text);
            }
        });
    }

    // handle save changes button here
    // handle save changes button clicked

      render () {

        return (
            <div className='row'>
                <div className='col-md-3'></div>
                <div className='col-md-6'>
                    <div className='panel panel-default'>
                        <div className='panel-body text-align-center'>Are you sure?</div>
                        <div className='panel-footer clearfix'>
                            <div className='text-align-center'>
                                <button onClick={this.onDelete}
                                    className='btn btn-danger m-r-1em'>Yes</button>
                                <button onClick={() => this.props.changeAppMode('read')}
                                    className='btn btn-primary'>No</button>
                            </div>
                        </div>
                    </div>
                </div>
                <div className='col-md-3'></div>
            </div>
        );
      }

    } 
    export default DeleteProductComponent; 

Answer 1

You in classs you need to bind this to the class. The best place to do it is in the constructor of the class as it will run only the first time the class instantiate rather then doing it inside the render method witch will create a new instance of the handler on each render.
So you should do this in the constructor:

    class DeleteProductComponent extends Component {
        constructor(props, context) {
            super(props, context);

            this.onDelete = this.onDelete.bind(this);
        }
    //.... rest of the class

Answer 2

Bind onDelete() function to the component by 2 ways:

In the constructor:

class DeleteProductComponent extends Component {

  constructor(props) {
    super(props);
    this.onDelete = this.onDelete.bind(this);
  }

  componentDidMount() {}

  onDelete() {}

  render() {}

}

Or use ES6's syntax for onDelete() (then it will be bound to the component by itself):

 onDelete = () => {

    var id = this.props.productId;

    $.ajax({
        url: "http://localhost/my-app/public/delete.php",
        type : "POST",
        contentType : 'application/json',
        data : JSON.stringify({'id' : id}),
        success : function(response) {
            this.props.changeAppMode('read');
        }.bind(this),
        error: function(xhr, resp, text){
            // show error in console
            console.log(xhr, resp, text);
        }
    });
  }