when should i use deep copying in javascript code example

Example 1: how to make a deep copy in javascript

JSON.parse(JSON.stringify(o))

Example 2: deep copy javascript

function copy(arr1, arr2) {
	for (var i =0; i< arr1.length; i++) {
    	arr2[i] = arr1[i];
    }
}
copy(arr1, arr2)