ReactJS - map 内的 Map

Question

I am working on a ReactJS & Redux app. At some point, I have a list of elements (notes), each one of them having an array (subtasks). I would like to display all the elements, and for each of them, display the content of their array.

I tried this:

 render(){
    return(
        <div>
            <h3>{this.props.match.params.user}'s board</h3>

            <Link to={`/settings/${this.props.match.params.user}`}>
                <button>Settings</button>
            </Link>

            <Link to={`/new/${this.props.match.params.user}`}>
                <button>Add note</button>
            </Link>

            {
                this.props.notes.map((item,index) => 
                    <Link to={`/details/${item.name}`}>
                        <h4 key={index}>{item.name}</h4>

                        item.subtasks.map((sub, subindex)=>
                            <p key={subindex}>{sub}</p>)

                    </Link>
                )
            }
        </div>
    );
}

But I got:

Uncaught ReferenceError: subindex is not defined

What's the right way to do it?

Answer 1

You need to wrap second map , inside {} brackets like this

{
    this.props.notes.map((item,index) => 
        <Link to={`/details/${item.name}`}>
            <h4 key={index}>{item.name}</h4>

            { 
                item.subtasks.map((sub, subindex) =>
                    <p key={subindex}>{sub}</p>)
            }

        </Link>
    )
}

Answer 2

An example with Vanilla JavaScript you can implement same way in react as you wish.

 let users = [ { name: "Amoos", skills: ["PHP", "MySQL"] }, { name: "Rifat", skills: ["JavaScript", "React", "HTML"] } ]; users.map(( user, index ) => { console.log(`User: ${user.name}`) { user.skills.map(( skill, subIndex) => { console.log(`Skill # ${subIndex}: ${skill} `) }) } } )