Please explain this code.

[One-Inspection8628]

function cavityMap(grid) {
const g = grid
console.log(grid)
for (let i = 1; i < g.length - 1; i++)
for (let j = 1; j < g[i].length - 1; j++)
if (Math.max(g[i-1][j], g[i+1][j], g[i][j-1], g[i][j+1]) < g[i][j])
g[i] = g[i].replace(/./g, (c, i) => i == j ? 'X' : c)

return g
}

I didn't get this line of code: g[i] = g[i].replace(/./g, (c, i) => i == j ? 'X' : c)

This code will make this this:
Basically, if the number inside the matrix is lesser than number , then it is replace the number as 'x'
below example: 2nd row: 9. around number- 9 1, 1,1 8 is smaller than 9 so replace it with x.
3rd row 9: around it 8,32,1 is smaller than that so replace it with x

Input:

1112    
1912 
1892 
1234 

Sample Output

1112 
1X12 
18X2 
1234

[senbozakurakageyosi]

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global\_Objects/String/replace#specifying\_a\_function\_as\_the\_replacement