freeCodeCamp/guide/english/certifications/javascript-algorithms-and-data-structures/basic-algorithm-scripting/finders-keepers/index.md

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Finders Keepers

Finders Keepers

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Problem Explanation

We need to return the element from an array that passes a function. Both the function and the array are passed into our function findElement(arr, func).

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Hints

Hint 1

We need to return the element from an array that passes a function. Both the function and the array are passed into our function findElement(arr, func). Looking through the array can be done with a for loop.

Hint 2

num is passed to the function. We will need to set it to the elements we want to check with the function.

Hint 3

Do not forget, if none of the numbers in the array pass the test, it should return undefined.

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Solutions

Solution 1 (Click to Show/Hide)

function findElement(arr, func) {
  let num = 0;

  for (var i = 0; i < arr.length; i++) {
    num = arr[i];
    if (func(num)) {
      return num;
    }
  }

  return undefined;
}

Code Explanation

• Challenge asks us to look through array. This is done using a for loop.
• The num variable is being passed into the function, so we set it to each index in our array.
• The pre-defined function already checks each number for us, so if it is "true", we return that num.
• If none of the numbers in the array pass the function's test, we return undefined.

Solution 2 (Click to Show/Hide)

function findElement(arr, func) {
  return arr.find(func);
}

Relevant Links

• Array.prototype.find

Solution 3 (Click to Show/Hide)

function findElement(arr, func) {
  return arr[arr.map(func).indexOf(true)];
}

Code Explanation

1. Look through the array given in the 1st paramater "arr" using the .map() method
2. Use the function in the 2nd parameter as the callback function in arr.map()
3. Acquire the index of the first number that meets the condition in the function.
4. Use that index to display the first available number that meets the condition.