Passing an additional parameter with an onChange event

Question

What I'm trying to do:

I am trying to pass a string from a child component to the handleChange function of a parent component.

What currently works:

I have a parent React JS class with the following method:

handleChange(event) {      console.log(event.target.value); } 

In the render function I have the following:

<Child handleChange={this.handleChange.bind(this)} /> 

In the Child class I have:

<fieldset onChange={this.props.handleChange}>     <div>Tag 1: <input id="tag1" value={tags[0]} /></div>     <div>Tag 2: <input id="tag2" value={tags[1]} /></div>     <div>Tag 3: <input id="tag3" value={tags[2]} /></div> </fieldset> 

This works fine.

What I am trying to do instead:

I am attempting to add a section parameter to the handleChange function as follows:

handleChange(section, event) {     console.log(section);     console.log(event.target.value); } 

And in the Child class I have:

<fieldset onChange={this.props.handleChange("tags")}>     <div>Tag 1: <input id="tag1" value={tags[0]} /></div>     <div>Tag 2: <input id="tag2" value={tags[1]} /></div>     <div>Tag 3: <input id="tag3" value={tags[2]} /></div> </fieldset> 

I now get the error:

Uncaught TypeError: Cannot read property 'target' of undefined 

This error is being thrown in my second console.log statement.

What am I doing wrong?

Also, I am considering making the section parameter optional. If so, is there an easy way to do this? It seems like it might not be possible if the event parameter needs to be last.

Answer 1

When you are writing this:

<fieldset onChange={this.props.handleChange("tags")}> 

handleChange will be called immediately as soon as render is triggered.

Instead, do it like this:

<fieldset onChange={(e) => this.props.handleChange("tags", e)}> 

Now the handleChange will be called when onChange handler is called.

Answer 2

In your handle event use double arrow function, there's no need to bind when using arrow function:

handleChange = tags => (event) => {     console.log(tags);     console.log(event.target.value); } 

And in the Child:

<fieldset onChange={this.props.handleChange("tags")}>     <div>Tag 1: <input id="tag1" value={tags[0]} /></div>     <div>Tag 2: <input id="tag2" value={tags[1]} /></div>     <div>Tag 3: <input id="tag3" value={tags[2]} /></div> </fieldset>