setState is not merging the values

Question

I use the following code in react in order to update state. state should finally looks like this:

this.state.output = {
 \'abc\':{
     value: 10
 }         


        

Answer 1

object spread syntax is recent spec. Here is the documentation for it: using-object-spread-operator

Below code uses Object.assign method instead :

handleChange = (data) => {
    this.setState(prevState => ({
        output: Object.assign({}, prevState, {
        [data.id]: data
      })
    })
)}

Answer 2

Because you forgot to add the other property and their values, update the object like this:

handleChange = (data) => {
    this.setState(prevState => {
        return {
            output: {
                ...prevState.output,      // notice this
                [data.id]: { ...data },
            },
        }
    })
}

Or simply:

handleChange = (data) => {
    this.setState(prevState => ({
        output: {
            ...prevState.output,
            [data.id]: { ...data },
        },
    })
)}