How do I update states `onChange` in an array of object in React Hooks
JavascriptReactjsReact HooksJavascript Problem Overview
I have retrieved datas stored using useState
in an array of object, the datas was then outputted into form fields. And now I want to be able to update the fields (state) as I type.
I have seen examples on people updating the state for property in array, but never for state in an array of object, so I don't know how to do it. I've got the index of the object passed to the callback function but I didn't know how to update the state using it.
// sample data structure
const datas = [
{
id: 1,
name: 'john',
gender: 'm'
}
{
id: 2,
name: 'mary',
gender: 'f'
}
]
const [datas, setDatas] = useState([]);
const updateFieldChanged = index => e => {
console.log('index: ' + index);
console.log('property name: '+ e.target.name);
setData() // ??
}
return (
<React.Fragment>
{datas.map((data, index) => {
<li key={data.name}>
<input type="text" name="name" value={data.name} onChange={updateFieldChanged(index)} />
</li>
})}
</React.Fragment>
)
Javascript Solutions
Solution 1 - Javascript
Here is how you do it:
// sample data structure
/* const data = [
{
id: 1,
name: 'john',
gender: 'm'
}
{
id: 2,
name: 'mary',
gender: 'f'
}
] */ // make sure to set the default value in the useState call (I already fixed it)
const [data, setData] = useState([
{
id: 1,
name: 'john',
gender: 'm'
}
{
id: 2,
name: 'mary',
gender: 'f'
}
]);
const updateFieldChanged = index => e => {
console.log('index: ' + index);
console.log('property name: '+ e.target.name);
let newArr = [...data]; // copying the old datas array
newArr[index] = e.target.value; // replace e.target.value with whatever you want to change it to
setData(newArr);
}
return (
<React.Fragment>
{data.map((datum, index) => {
<li key={datum.name}>
<input type="text" name="name" value={datum.name} onChange={updateFieldChanged(index)} />
</li>
})}
</React.Fragment>
)
Solution 2 - Javascript
You can do this without mutation by mapping your old array into a new one, swapping what you want to change for an updated item along the way.
setDatas(
datas.map(item =>
item.id === index
? {...item, someProp : "changed"}
: item
))
Solution 3 - Javascript
setDatas(datas=>({
...datas,
[index]: e.target.value
}))
with index being the target position and e.target.value the new value
Solution 4 - Javascript
You don't even need to be using the index ( except for the key if you want ) nor copying the old datas array,and can even do it inline or just pass data as an argument if you prefer updateFieldChanged to not be inline. It's done very quickly that way :
const initial_data = [
{
id: 1,
name: "john",
gender: "m",
},
{
id: 2,
name: "mary",
gender: "f",
},
];
const [datas, setDatas] = useState(initial_data);
return (
<div>
{datas.map((data, index) => (
<li key={index}>
<input
type="text"
value={data.name}
onChange={(e) => {
data.name = e.target.value;
setDatas([...datas]);
}}
/>
</li>
))}
</div>
);
};
Solution 5 - Javascript
This is what I do:
const [datas, setDatas] = useState([
{
id: 1,
name: "john",
gender: "m",
},
{
id: 2,
name: "mary",
gender: "f",
},
]);
const updateFieldChanged = (name, index) => (event) => {
let newArr = datas.map((item, i) => {
if (index == i) {
return { ...item, [name]: event.target.value };
} else {
return item;
}
});
setDatas(newArr);
};
return (
<React.Fragment>
{datas.map((data, index) => {
<li key={data.name}>
<input
type="text"
name="name"
value={data.name}
onChange={updateFieldChanged("name", index)}
/>
</li>;
<li key={data.gender}>
<input
type="text"
name="gender"
value={data.gender}
onChange={updateFieldChanged("gender", index)}
/>
</li>;
})}
</React.Fragment>
);
Solution 6 - Javascript
Spread the array before that. As you cannot update the hook directly without using the method returned by useState
const newState = [...originalState]
newState[index] = newValue
setOriginalState(newState)
This will modify the value of the state and update the useState hook if its an array of string.
Solution 7 - Javascript
const updateFieldChanged = index => e => {
name=e.target.name //key
let newArr = [...data]; // copying the old datas array
newArr[index][name] = e.target.value; //key and value
setData(newArr);
}
return (
<React.Fragment>
{data.map((datum, index) => {
<li key={datum.name}>
<input type="text" name="name" value={datum.name} onChange={updateFieldChanged(index)} />
</li>
})}
</React.Fragment>
)
Solution 8 - Javascript
Base on @Steffan, thus use as your way:
const [arr,arrSet] = useState(array_value);
...
let newArr = [...arr];
arr.map((data,index) => {
newArr[index].somename= new_value;
});
arrSet(newArr);
Use useEffect to check new arr value.
Solution 9 - Javascript
A little late to the party, but it is an option to spread the contents of the array in a new object, then replacing the desired object in the selected index and finally producing an array from that result, it is a short answer, probably not the best for large arrays.
// data = [{name: 'tom', age: 15, etc...}, {name: 'jerry', age: 10, etc...}]
// index = 1
setData(Object.values({...data, [index]: {...data[index], name: 'the mouse' }}))
// data = [{name: 'tom', age: 15, etc...}, {name: 'the mouse', age: 10, etc...}]