Greatest number in a dynamically typed array in JavaScript

We are required to write a JavaScript function that takes in an array that contains some numbers, some strings and some false values. Our function should return the biggest Number from the array.

For example: If the input array is −

const arr = [23, 'hello', undefined, null, 21, 65, NaN, 1, undefined, 'hii'];

Then the output should be 65.

Using Math.max with Array Filtering

The most straightforward approach is to filter valid numbers first, then use Math.max():

const arr = [23, 'hello', undefined, null, 21, 65, NaN, 1, undefined, 'hii'];

const pickBiggest = arr => {
    const validNumbers = arr.filter(item => typeof item === 'number' && !isNaN(item));
    return Math.max(...validNumbers);
};

console.log(pickBiggest(arr));

65

Using Manual Loop with Type Checking

For more control over the filtering process, we can manually iterate and check each element:

const arr = [23, 'hello', undefined, null, 21, 65, NaN, 1, undefined, 'hii'];

const pickBiggest = arr => {
    let max = -Infinity;
    
    for(let i = 0; i < arr.length; i++){
        // Check if it's a valid number
        if(typeof arr[i] === 'number' && !isNaN(arr[i])){
            max = Math.max(max, arr[i]);
        }
    }
    
    return max === -Infinity ? undefined : max;
};

console.log(pickBiggest(arr));

65

Using Reduce Method

The reduce() method provides a functional programming approach to find the maximum:

const arr = [23, 'hello', undefined, null, 21, 65, NaN, 1, undefined, 'hii'];

const pickBiggest = arr => {
    return arr.reduce((max, current) => {
        if(typeof current === 'number' && !isNaN(current)){
            return Math.max(max, current);
        }
        return max;
    }, -Infinity);
};

console.log(pickBiggest(arr));

65

Comparison of Methods

Key Points

• typeof item === 'number' ensures we only consider numeric values
• !isNaN(item) excludes NaN values which are technically numbers
• -Infinity serves as the initial maximum value for comparison
• All methods handle mixed data types effectively

Conclusion

When finding the greatest number in a mixed array, filter valid numbers first using type checking and NaN validation. The filter + Math.max approach offers the best balance of readability and functionality.