explain for-in loop in js code example

Example 1: for in loop javascript

let array = [1,2,3,4,5,6,7,8,9,10]; 
// our array that we will use the for loop on
for (let i = 0; i < array.length; i++) { 
  // this loop will console log the element at array[i] starting at 0
  // and will continue looping for i < array.length 
  console.log(array[i]);
  // after each loop i will increase by 1
}

// this will console log
// 1
// 2
// 3
// 4
// 5
// 6
// 7
// 8
// 9
// 10

Example 2: for in loop javascript

function diagonalDifference(arr) {
    // Write your code here
    // return (arr); 11,2,4,4,5,6,10,8,-12
    let n = arr.length;
    let pri,sec = 0;

    pri = sec = 0; //initialize both diagonal sum to 0
    for (let i= 0; i < n; i++) {
        //console.log( "PRI(arr)= ", i,i);
        //console.log( arr[i][i]);
        //console.log( "SEC(arr)= ", i,n-i-1);
        //console.log( arr[i][n-i-1]);
        pri += arr[i][i];
        sec += arr[i][n - i - 1]; 
    }
	
  	// return |x| is the absolute value of x
    if(pri==sec){
        return (0);
    }else {
        if (pri>sec){
            return (pri-sec);
        }else{
            return (sec-pri);
        }
    }
}