Shift certain array elements to front of array - JavaScript

We are required to write a JavaScript function that takes in an array of numbers. The function should bring all the 3-digit integers to the front of the array.

Let's say the following is our array of numbers:

const numList = [1, 324, 34, 3434, 304, 2929, 23, 444];

Understanding 3-Digit Numbers

A 3-digit number is any integer between 100 and 999 (inclusive). We can check this using a simple condition:

const isThreeDigit = num => num > 99 && num 

true
false
false


Example

Here's the complete solution that moves all 3-digit numbers to the front:

const numList = [1, 324, 34, 3434, 304, 2929, 23, 444];

const isThreeDigit = num => num > 99 && num  {
    for(let i = 0; i 

[
  444, 304, 324,
    1,  34, 3434,
  2929, 23
]


How It Works

The algorithm works by:

• Iterating through the array: We loop through each element
• Checking if it's a 3-digit number: Using the isThreeDigit helper function
• Moving to front: If it's a 3-digit number, we use splice(i, 1)[0] to remove it from its current position and unshift() to add it to the beginning
• Skipping non-3-digit numbers: We use continue to skip elements that don't meet our criteria

Alternative Approach Using Filter

Here's a cleaner approach using array methods:

const numList2 = [1, 324, 34, 3434, 304, 2929, 23, 444];

const isThreeDigit = num => num > 99 && num  {
    const threeDigit = arr.filter(isThreeDigit);
    const others = arr.filter(num => !isThreeDigit(num));
    return [...threeDigit, ...others];
};

const result = moveThreeDigitToFront(numList2);
console.log(result);

[ 324, 304, 444, 1, 34, 3434, 2929, 23 ]

Conclusion

Both approaches successfully move 3-digit numbers to the front of the array. The splice/unshift method modifies the original array in place, while the filter method creates a new array with the desired order.