Link to Problem: https://leetcode.com/problems/longest-mountain-in-array/

Hi All, I've been working on longest mountain in array on Leetcode. I've come up with a solution that passes the test but only beats 17% of javascript submissions. I just want to know if there's anything I can do with my code to optimize it's performance. Also please let me know if the code could be written better.

var longestMountain = function(A) {

let maxDifference = 0;
let startPeakEnd = [];
const start = [];
const innerLoop = [];

if(A[1]>A[0])start.push(0)
else start.push(1);

for(let i = 0; i < A.length; i++){
    if(A[i-1]<A[i] && A[i+1]<A[i]){
        startPeakEnd.push(i);
    }else if(A[i-1]>=A[i] && A[i+1]>=A[i]){
        startPeakEnd.push(i);
        innerLoop.push([start.pop(),...startPeakEnd]);
        start.push(i)
        startPeakEnd = [];
    }else if(A[i+1]===undefined){
        startPeakEnd.push(i);
        innerLoop.push([start.pop(),...startPeakEnd]);
    }
}

for(let item of innerLoop){
    if(item.length===3){
        if(item[2]-item[0]+1>maxDifference){
            maxDifference=item[2]-item[0]+1;
        }
    }
}

return maxDifference;

};

I've been working on longest mountain in array on Leetcode:

Let's call any (contiguous) subarray B (of A) a mountain if the following properties hold:

• B.length >= 3
• There exists some 0 < i < B.length - 1 such that B[0] < B[1] < ... B[i-1] < B[i] > B[i+1] > ... > B[B.length - 1]

(Note that B could be any subarray of A, including the entire array A.)

Given an array A of integers, return the length of the longest mountain.

Return 0 if there is no mountain.

Example:

Input: [2,1,4,7,3,2,5]
Output: 5
Explanation: The largest mountain is [1,4,7,3,2] which has length 5.

I've come up with a solution that passes the test but only beats 17% of javascript submissions. I just want to know if there's anything I can do with my code to optimize it's performance. Also please let me know if the code could be written better.

var longestMountain = function(A) {

    let maxDifference = 0;
    let startPeakEnd = [];
    const start = [];
    const innerLoop = [];

    if(A[1]>A[0])start.push(0)
    else start.push(1);

    for(let i = 0; i < A.length; i++){
        if(A[i-1]<A[i] && A[i+1]<A[i]){
            startPeakEnd.push(i);
        }else if(A[i-1]>=A[i] && A[i+1]>=A[i]){
            startPeakEnd.push(i);
            innerLoop.push([start.pop(),...startPeakEnd]);
            start.push(i)
            startPeakEnd = [];
        }else if(A[i+1]===undefined){
            startPeakEnd.push(i);
            innerLoop.push([start.pop(),...startPeakEnd]);
        }
    }
    
    for(let item of innerLoop){
        if(item.length===3){
            if(item[2]-item[0]+1>maxDifference){
                maxDifference=item[2]-item[0]+1;
            }
        }
    }

    return maxDifference;

};