behold.js

/**
 * @param {number[]} arr
 * @param {number} k
 * @return {number}
 */
var kConcatenationMaxSum = function(arr, k) {
    const anyNegative = arr.some(a => a < 0);
    
    if (!anyNegative) {
        return (arr.reduce((a, b) => a + b, 0) * k) % 1000000007;
    }
    
    const allNegative = arr.every(a => a <= 0);
    
    if (allNegative) { return 0; }
    
    const maxSingle = maxSubArray(arr) % 1000000007;
    
    if (k === 1) {
        return maxSingle;
    }
    
    const doubleArr = [...arr, ...arr];
    const maxDouble = maxSubArray(doubleArr) % 1000000007;
    
    if (k === 2) {
        return maxDouble;
    }
    
    const tripleArr = [...arr, ...arr, ...arr];
    const maxTriple = maxSubArray(tripleArr) % 1000000007;
    
    if (k === 3) {
        return maxTriple;
    }
    
    if (maxDouble === maxTriple) {
        return maxDouble;
    }
    
    return (maxSingle + ((maxTriple - maxDouble) * (k - 1))) % 1000000007; 
    
};

const maxSubArray = (nums) => {
    let maxTotal = nums[0];
    let sum = 0;
    
    for(let i of nums) {
        sum += i;
        if(maxTotal < sum) {
            maxTotal = sum;
        }
        if(sum < 0) {
            sum = 0;
        }
    }
    
    return maxTotal;
};

reason for this code??

 if (maxDouble === maxTriple) {
        return maxDouble;
    }