Variable automatically change in typescript

Question

I have method which take interface parameter. But i want that my original parameter "selectItemList" not change. So, I create new constant "itemlist". And I added item to "itemList".But, when I added item to itemList, then automatically added to selectItemList. I want only change "itemList" not " selectItemList". Where is my mistake?

SelectItem.ts (Interface)

export interface SelectItem {
    label?: string;
    value: any;
    styleClass?: string;
    icon?: string;
    title?: string;
    disabled?: boolean;
}

My method

  addUnselectedItem(selectItemList: SelectItem[]): SelectItem[] {
    const itemList = selectItemList;
    itemList.unshift({ value: "", label: "Please Select" });
    return itemList;
  }

i hope this will help you. stackblitz.com/edit/angular-gp1t3t?file=src/app/… — shubham singh
– shubham singh, Commented Oct 8, 2018 at 12:26
Thanks @shubhamsingh. This answer also worked like Sarthak Aggarwal's answer. — realist
– realist, Commented Oct 8, 2018 at 12:33

Sarthak Aggarwal · Accepted Answer · 2018-10-08 12:18:30Z

3

You are making reference of 'selectItemList' in 'itemList'. You need to create new array to solve the above problem.

There are 2 methods to do the same.

copy all the elements in new array and then modify new array
use 'slice' method(returns a shallow copy of a portion of an array) of Array.

const itemList = selectItemList.slice(0,selectItemList.length);

answered Oct 8, 2018 at 12:18

Sarthak Aggarwal

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