使用速记更新对象和setState的数组

Question

Was trying to rewrite my update array of object using shorter version but failed, I have a working version, which assign to a tempporary variable before setState.

//working version
const new_items = (this.state.new_items || []).map((o, i) => {
    if(i === idx) {
        return e.target.value
    }
    return o
})
this.setState({
    items: new_items
})

//shorter version but why snytax error?
this.setState({
    items: (this.state.items || []).map((o, i)=> ({
        i === idx ? e.target.value : o
    }))
})

Answer 1

You need to return the e.target.value or the o . As is, the inside of your map function is just an orphaned expression that's not connected to anything, which won't work.

Best thing to do would be to have the arrow function implicitly return, by removing the { } s:

this.setState({
  items: (this.state.templates || []).map((o, i) => (
    i === idx ? e.target.value : o
  ))
});