使用js写一个方法，使得数组的某个元素置顶

/**
 * Moves the element at the specified index to the beginning of the array.
 *
 * @param {Array} arr The array to modify.
 * @param {number} index The index of the element to move to the top.
 * @returns {Array} The modified array with the element at the top.  Returns the original array if the index is invalid.
 */
function moveToTop(arr, index) {
  if (index < 0 || index >= arr.length) {
    return arr; // Invalid index, return original array
  }

  const element = arr.splice(index, 1)[0]; // Remove the element at the specified index
  arr.unshift(element); // Add the removed element to the beginning of the array

  return arr;
}


// Example usage:
const myArray = ['apple', 'banana', 'orange', 'grape'];

console.log(moveToTop(myArray, 1)); // Output: ['banana', 'apple', 'orange', 'grape']
console.log(moveToTop(myArray, 3)); // Output: ['grape', 'banana', 'apple', 'orange']

// Example with invalid index:
console.log(moveToTop(myArray, -1)); // Output: ['grape', 'banana', 'apple', 'orange'] (no change)
console.log(moveToTop(myArray, 4));  // Output: ['grape', 'banana', 'apple', 'orange'] (no change)


// More robust version using slice to avoid modifying the original array if the index is invalid:

function moveToTopImmutable(arr, index) {
  if (index < 0 || index >= arr.length) {
    return arr.slice(); // Return a copy of the original array
  }

  return [arr[index], ...arr.slice(0, index), ...arr.slice(index + 1)];
}

const myArray2 = ['apple', 'banana', 'orange', 'grape'];
console.log(moveToTopImmutable(myArray2, 1)); // Output: ['banana', 'apple', 'orange', 'grape']
console.log(myArray2); // Output: ['apple', 'banana', 'orange', 'grape'] (original array unchanged)

This code provides two functions:

• moveToTop(arr, index): Modifies the original array directly. If you need to preserve the original array, use the second function.
• moveToTopImmutable(arr, index): Creates a new array with the element moved to the top, leaving the original array unchanged. This is generally preferred in functional programming paradigms. It uses the spread syntax (...) for a concise way to create the new array.

Both functions handle invalid indices gracefully by returning the original array (or a copy of it in the immutable version). The examples demonstrate how to use the functions and show the output. The comments explain the logic clearly.