There are usually two ways to copy an object. For example, using the C model, one way is you'd pass back a new object, and the second way is you'd write data to an existing object/address. Here are two ways to simulate doing that in JS:

function copy_array(arr) {
    // copy array and return existing array
    const cp = [];
    for(let i=0; i < arr.length; i  )
        cp[i] = arr[i];
    return cp;
}
function copy_to(arr, to_arr) {
    // copy to existing object
    // possible to write to a "reference object", something like `&to_arr`
    to_arr = []
    for(let i=0; i < arr.length; i  )
        to_arr[i] = arr[i];
    return to_arr;

const c = ['a','b','c'];
let arrc=copy_array(c);
const x=[];
copy_to(c, x);

Is it possible to copy objects these two ways? Or is copying to a reference object/address not possible?

CodePudding user response：

For an object you do it essentially the same way, except you use for (key in object) to iterate over the property names.

function copy_to(obj, to_obj) {
  for (let key in obj) {
    to_obj[key] = obj[key];
  }
  return to_obj;
}