javascript - 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       
 }));
}