I want to form an array from an existing array so I can modify the new array without affecting the old. I realise arrays are mutable and this is why the new array affects the old.
E.g.
old = ["Apples", "Bananas"];
new = old;
new.reverse();
Old has also been reversed.
In Python, I can just do new = list(old), but doing new = new Array(old); puts the old list inside a list.
You can use the .slice method:
var old = ["Apples", "Bananas"];
var newArr = old.slice(0);
newArr.reverse();
// now newArr is ["Bananas", "Apples"] and old is ["Apples", "Bananas"]
Array.prototype.slice returns a shallow copy of a portion of an array. Giving it 0 as the first parameter means you are returning a copy of all the elements (starting at index 0 that is)
old.slice() since 0 is the default. See slice() docs
array.values() method which copies the values like this. Unfortunately, no other browsers support the method.
var oldArr = [ [1,2], [3,4] ] and did var newArr = oldArr.slice(0) and then change newArr with newArr[1][0] = 5 and check oldArr[0][0] you will notice it will be updated too. So the only way to copy and to loop through and slice each value
JSON.parse(JSON.stringify(old)) though that's rarely a useful thing to do.
Try the following
newArray = oldArray.slice(0);
var arrOld = ["Apples", "Bananas"]; var arrNew= [...arrOld];