How to pass arguments to functions in React js?

Question

1. I want to display person's email in the alert window. But, I do not know how to pass email as arguments to displayAlert method. Also, it wont let me use either. So, I have to assign displayAlert methos to a variable and use it in onClick. I do not know why it wont let me call it directly.

   class People extends React.Component{
   render (){
           var handleClick = this.displayAlert;
           var items = this.props.items.map(function(item) {
               return(
                   <ul key = {item.id}>
                       <li>
                           <button onClick= {handleClick}>{item.lastName + ', ' + item.firstName}</button>
                       </li>
                   </ul>
               )
           });
           return (<div>{items}</div>);
    }
   
   displayAlert (){
       alert('Hi');
   }
   }
   
    class PersonList extends React.Component{
        render () {
           return (
       <div>
           <People items={this.props.people}/> /* People is an array of people*/
       </div>
       );
     }
   }
   

Answer 1

The ES6 way:

Using arrow functions =>

const items = this.props.items.map((item) => (
  <ul key={item.id}>
    <li>
      <button onClick={() => this.displayAlert(item.email)}>
        {item.lastName + ', ' + item.firstName}
      </button>
    </li>
  </ul>
));

onClick the anonymous function is called and executes this.displayAlert(item.email)

The ES5 way:

You could do this using .bind and passing the parameter in there.

You should also pass this or use bind to keep the proper context on your .map function:

var items = this.props.items.map(function(item) {
  return (
    <ul key={item.id}>
      <li>
        <button onClick={this.displayAlert.bind(this, item.email)}>
          {item.lastName + ', ' + item.firstName}
        </button>
      </li>
    </ul>
  );
}, this);

Shown in the example here: React - Communicate Between Components

Answer 2

Using arrow function and babel plugin "transform-class-properties"

class People extends React.Component {
  render() {
    return (
      <ul>
        { this.props.items.map( (item) => (
          <li key={item.id}>
            <button onClick={this.displayAlert(item)}>
              {item.lastName + ', ' + item.firstName}
            </button>
          </li>
        ))}
      </ul>
    )
  }

  displayAlert = (item) => (event) => {
    // you can access the item object and the event object
    alert('Hi');
  }
}