Cloning an array in Javascript/Typescript

Question

I have array of two objects:

genericItems: Item[] = [];
backupData: Item[] = [];

I am populating my HTML table with genericItemsdata. The table is modifiable. There is a reset button to undo all changes done with backUpData. This array is populated by a service:

getGenericItems(selected: Item) {
this.itemService.getGenericItems(selected).subscribe(
  result => {
     this.genericItems = result;
  });
     this.backupData = this.genericItems.slice();
  }

My idea was that, the user changes will get reflected in first array and second array can be used as backup for reset operation. The issue I am facing here is when the user modifies the table (genericItems[]) the second array backupData also gets modified.

How is this happening and how to prevent this?

Answer 1

Clone an object:

const myClonedObject = Object.assign({}, myObject);

Clone an Array:

• Option 1 if you have an array of primitive types:

const myClonedArray = Object.assign([], myArray);

• Option 2 - if you have an array of objects:

const myArray= [{ a: 'a', b: 'b' }, { a: 'c', b: 'd' }];
const myClonedArray = [];
myArray.forEach(val => myClonedArray.push(Object.assign({}, val)));