JIYIK CN >

Finding objects in an array in React:

1. Call the method on the array find(), passing it a function.
2. The function should return an equality check on the relevant attributes.
3. find()The method returns the first value in the array that satisfies the condition.

const App = () => {
  const arr = [
    {id: 1, country: 'Austria'},
    {id: 2, country: 'Germany'},
    {id: 3, country: 'Austria'},
  ];

  // ✅ Find first object that matches condition
  const found = arr.find(obj => {
    return obj.id === 1;
  });

  // 👇️ {id: 1, country: 'Austria'}
  console.log(found);

  // -----------------------

  // ✅ Find multiple objects that satisfy condition
  const filtered = arr.filter(obj => {
    return obj.country === 'Austria';
  });

  // 👇️ [{id: 1, country: 'Austria'}, {id: 3, country: 'Austria'}]
  console.log(filtered);

  return (
    <div>
      {/* 👇️ render single object */}
      {found && (
        <div>
          <h2>id: {found.id}</h2>
          <h2>country: {found.country}</h2>
        </div>
      )}

      <hr />

      {/* 👇️ render array of objects */}
      {filtered.map(obj => {
        return (
          <div key={obj.id}>
            <h2>id: {obj.id}</h2>
            <h2>country: {obj.country}</h2>
          </div>
        );
      })}
    </div>
  );
};

export default App;

The code examples show how to:

1. Find the first object in an array that matches a condition
2. Find multiple objects that meet a condition

The function we pass to Array.find()the method is called for each element (object) in the array until it returns a true value or the entire array is exhausted.

In each iteration, we check if the object's id property is equal to 1.

If the condition returns true, find()the method returns the corresponding object and short-circuits.

This is very convenient when we only need to get the first object that meets a certain condition.

There is no wasted iteration because once the condition is met, find()the method short-circuits and returns the object.

If the callback function we pass to the find method never returns a true value, the find method returns undefined.

const arr = [
    {id: 1, country: 'Austria'},
    {id: 2, country: 'Germany'},
    {id: 3, country: 'Austria'},
  ];

  const notFound = arr.find(obj => {
    return obj.id === 123;
  });
  console.log(notFound); // 👉️ undefined

That's &&why we use the logical operator - to check if the found variable stores a truth value.

Use filter()the method to find multiple objects that meet a condition in a React array. filter()The method accepts a function as a parameter and returns an array containing only the elements that meet the condition.

const App = () => {
  const arr = [
    {id: 1, country: 'Austria'},
    {id: 2, country: 'Germany'},
    {id: 3, country: 'Austria'},
  ];

  // ✅ Find multiple objects that satisfy condition
  const filtered = arr.filter(obj => {
    return obj.country === 'Austria';
  });

  // 👇️ [{id: 1, country: 'Austria'}, {id: 3, country: 'Austria'}]
  console.log(filtered);

  return (
    <div>
      {/* 👇️ render array of objects */}
      {filtered.map(obj => {
        return (
          <div key={obj.id}>
            <h2>id: {obj.id}</h2>
            <h2>country: {obj.country}</h2>
          </div>
        );
      })}
    </div>
  );
};

export default App;

The function we pass to Array.filter()the method will be called for each element in the array.

If the function returns a true value, the element will be added to filter()the array returned by the method.

请注意, the filter method will iterate over the entire array no matter how many times the condition is met.

In this way, we can get multiple objects that meet the conditions from the object array.

In other words, we filter the array to contain only objects that satisfy the condition.

If the callback function we pass to the filter method never returns a true value, the filter method returns an empty array.

We can Array.map()render an array of objects in our React component using the render method.