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VisualizaçõesHow to use .filter inside ReactJs Component
I'm Using React for the first time and I am trying to filter a JSON response so that I can display a list of products.
When I log the result of the filter to the console I seem to get the correct data. However when I try and map over it and render it ".Products" seems to be undefined.
import React, { useContext } from 'react';
import { MenuContext } from '../context/menuContext';
function Category() {
const [categoryItems] = useContext(MenuContext);
const category = categoryItems.filter(element => element.CategoryName == "Rice");
console.log(category);
return (
<div>
<h1>Category Page</h1>
{category.Products.map(productItem => (
<h3 key={productItem.Id}>{productItem.ProductName}</h3>
))}
</div>
);
}
export default Category;
Update: Thanks @Ori Drori for your comment. I have tried to use .find and still does not work.
I think this is something to do with how react works. Becuase in the console I am getting an empty output before I get the correct result.
Update 2: I implemented the answer that I have marked as correct and its now working. HOWEVER. There are two things I don't understand and I would like someone to explain.
- When I call
console.log(console.log(category);
Why is it that in the console I see 'undefined' before I get the result with the data.
- Why do I need to put 'category &&' when I remove it. It stops working.
2 Respostas
Responde à pergunta0
category is a list, not a single object. The output of an Array.filter is always a list. That is why: category.Product is undefined.
If you want to find a category with the name Rice, you can change the code to:
import React, { useContext } from "react";
import { MenuContext } from "../context/menuContext";
function Category() {
const [categoryItems] = useContext(MenuContext);
const category = categoryItems.find(
(element) => element.CategoryName === "Rice",
); // change `filter` to `find` and `==` to `===`
console.log(category);
return (
<div>
<h1>Category Page</h1>
{category && // add this because category can be undefined
category.Products.map((productItem) => (
<h3 key={productItem.Id}>{productItem.ProductName}</h3>
))}
</div>
);
}
export default Category;
If it still does not work, show the error and also console.log category.Products
0
When you used the method filter it returns as an array:
category.map(()=>)
or use the method to find the item product in category:
const find = category.find(elem=>elem.product)
find.map(()=>)