Object is not extensible error when creating new attribute for array of objects

Question

I have a function that needs to extend a javascript array, including a new attribute called selected:

export const initSelect = (data) => {      let newData = data.concat();     newData.map((item) => {         item.selected = false;     })      return newData; } 

data is a ReactJS state value (comes from this.state.data when calling the function), but this didn't seem to be a problem as newData is a new copy of data array...

I'm getting the following error:

TypeError: Cannot add property selected, object is not extensible 

Answer 1

You probably need to copy the objects:

export const initSelect = (data) => {  return data.map((item) => ({      ...item,      selected: false         })); }