JavaScript, Array Examples

Give example where all three parameters are used in predicate function in JS:

const numbers = [4, 9, 16, 25, 29];

      let first = numbers.findIndex(myFunction);

      console.log('Number above 18:',numbers[first])

      function myFunction(value, index, array) {

        return value > 18;

      }

Here's an example where all three parameters (value, index, and array) are used in the myFunction predicate function. Let’s modify myFunction to check if the value is above 18, is in an even index position, and is part of an array that has at least five elements.

const numbers = [4, 9, 16, 25, 29];

let first = numbers.findIndex(myFunction);

console.log('Number above 18:', numbers[first]);

function myFunction(value, index, array) {

  // Check if the value is above 18, is at an even index, and the array has at least 5 elements

  return value > 18 && index % 2 === 0 && array.length >= 5;

}

In this example:

value > 18 checks if the number is above 18.

index % 2 === 0 checks if the index is even.

array.length >= 5 checks if the array has at least 5 elements.

When you run this code, it will log the first number above 18 that is at an even index in an array with at least 5 elements.

Question:

Why I get position 4:

      const numArr = [4, 9, 11, 19];

      let position = numbers.findIndex(myFunction);

      console.log("position:", position);

      console.log("Number above 18:", numArr[first]);

      function myFunction(value, index, array) {

        // Check if the value is above 18, is at an even index,

        // and the array has at least 5 elements

        return value > 18 && index % 2 === 0 && array.length >= 5;

      }

The reason you're getting position 4 in your output is due to a mismatch between the variable names in your code. Specifically, you're using numbers in the line let position = numbers.findIndex(myFunction); instead of numArr, which is the array you intended to search through.

Here’s the corrected code:

const numArr = [4, 9, 11, 19];

let position = numArr.findIndex(myFunction); // Use numArr here

console.log("position:", position);

console.log("Number above 18:", numArr[position]);

function myFunction(value, index, array) {

  // Check if the value is above 18, is at an even index,

  // and the array has at least 5 elements

  return value > 18 && index % 2 === 0 && array.length >= 5;

}

Explanation

numArr only has 4 elements, so array.length >= 5 will evaluate as false for each element in myFunction.

Since findIndex returns -1 if no elements match the condition, position will be -1.

So, after fixing the variable name, the output will correctly be:

position: -1

Number above 18: undefined

This is because none of the elements meet all the conditions (value above 18, even index, and array length of at least 5).