javascript - How to avoid bind or inline arrow functions inside render method

Question

We should avoid method binding inside render because during re-rendering it will create the new methods instead of using the old one, that will affect the performance.

So for the scenarios like this:

<input onChange = { this._handleChange.bind(this) } ...../>

We can bind _handleChange method either in constructor:

this._handleChange = this._handleChange.bind(this);

Or we can use property initializer syntax:

_handleChange = () => {....}

Now lets consider the case where we want to pass some extra parameter, lets say in a simple todo app, onclick of item i need to delete the item from array, for that i need to pass either the item index or the todo name in each onClick method:

todos.map(el => <div key={el} onClick={this._deleteTodo.bind(this, el)}> {el} </div>)

For now just assume that todo names are unique.

As per DOC:

The problem with this syntax is that a different callback is created each time the component renders.

Question:

How to avoid this way of binding inside render method or what are the alternatives of this?

Kindly provide any reference or example, thanks.

Answer 1

First: A simple solution will be to create a component for the content inside a map function and pass the values as props and when you call the function from the child component you can pass the value to the function passed down as props.

Parent

deleteTodo = (val) => {
    console.log(val)
}
todos.map(el => 
    <MyComponent val={el} onClick={this.deleteTodo}/> 

)

MyComponent

class MyComponent extends React.Component {
    deleteTodo = () => {
        this.props.onClick(this.props.val);
    }
    render() {
       return <div  onClick={this.deleteTodo}> {this.props.val} </div>
    }
}

Sample snippet

class Parent extends React.Component {
     _deleteTodo = (val) => {
        console.log(val)
    }
    render() {
        var todos = ['a', 'b', 'c'];
        return (
           <div>{todos.map(el => 
             <MyComponent key={el} val={el} onClick={this._deleteTodo}/> 
        
           )}</div>
        )
    }
    
   
}

class MyComponent extends React.Component {
        _deleteTodo = () => {
                     console.log('here');   this.props.onClick(this.props.val);
        }
        render() {
           return <div onClick={this._deleteTodo}> {this.props.val} </div>
        }
    }
    
ReactDOM.render(<Parent/>, document.getElementById('app'));

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="app"></div>