push element from one array to another on button click in React?

Question

I am trying to use the method .contact() to push on element in my old_array to my new_array. I have one button on each element in the array like this:

´´´

<li key={i}>
   {{character.name} + "is" + {character.age} + "years old"}
   <button onClick={this.addToNewArray}>Fav</button>
</li>

´´´

so as you can see each element got a seperate id. Now i want to click the button to push that element to a new array . (i get data from API that i .map() into my old_array) My function looks like this:

´´´

constructor(props){
        super(props);
        this.state = {
            old_arary: [],
            new_array: []
        }
    }
addToNewArray = () => {
        let new_array = this.state.new_array.contact(this.state.old_array);
        this.setState({ new_array: new_array})

}

´´´

This is where i want my output:

´´´

<li>
   {this.state.new_array}
</li>

´´´

You are directly mutating the state which is not recommended when you are concating old_array and new_array. Instead you should be using setState method. — Nurul Sundarani
– Nurul Sundarani, Commented May 10, 2020 at 13:14
Now it seems to work BUT i get a huge error: gyazo.com/bb68e6fc3837f4ccc2e979305e48e379, it has something to do with the api? — gospecomid12
– gospecomid12, Commented May 10, 2020 at 13:30

Vivek Doshi · Accepted Answer · 2020-05-10 13:46:54Z

3

First :

in your question , you are using contact() everywhere, and I think there is no such function for array in JS :) , that should be concat()

Second :

You can use ES6 for lower code, something like this:

let new_array = [...this.state.new_array , ...this.state.old_array];
this.setState({ new_array });

Third :

Change this

<li>
   {this.state.new_array}
</li>

To :

{
    this.state.new_array.map((obj,index) => (
        <li key={index}>
            {obj.name}
        </li>
    ))
}

edited May 10, 2020 at 13:46

answered May 10, 2020 at 13:22

Vivek Doshi

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6 Comments

gospecomid12 Over a year ago

Now it seems to work BUT i get a huge error: gyazo.com/bb68e6fc3837f4ccc2e979305e48e379, it has something to do with the api?

Vivek Doshi Over a year ago

I think you are not getting array, it might be object, try this let new_array = [...this.state.new_array , this.state.old_array]; if it works then its object and not array

gospecomid12 Over a year ago

Yes, it is objects im getting, i tried to change the output to {this.state.new_array.toString()} and i got [object Object],[object Object],... on my screen

Vivek Doshi Over a year ago

@gospecomid12, that is array my friend, it would be great if you can create a demo and share link, have to debug, this way it won't be possible.

gospecomid12 Over a year ago

i actually made it work! i had to iterate over the array using map for it to display correctly.

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