Don't repeat the code...
In React, like anywhere else in your code, you must never repeat yourself unless it is strictly necessary (almost never).
Probably what you're going to read, it's easy stuff, but reading some code online, I thought about dealing with the subject ... I "apologize" to the experts for the banality.
Example...
We have to manage a text input tag, and make sure to memorize the value entered by the user, and show It somewhere, till it's changed again!
How do we do it in React?
We insert an onChange
that updates the state
of the component to the last input value ... and then we pass the value of the state
to the input tag, or to any other tag on the page, to show the last input value.
To the code!
//we've a class... with a state defined
class App extends Component {
constructor(props){
super(props)
this.state={
myFirstState:"Labrador"
}
//we're going to manage the changes, and setState() equal to the user input
valueChange = (e) => {
this.setState({myFirstState : e.target.value});
}
//rendering time...we've an Input tag, with the state as value
//and the function, calling to onChange
render() {
return (
<div className="just a class">
<input placeholder="insertValue" value={this.state.myFirstState}
onChange= {this.valueChange(e)}/>
</div>
)
}
}
That's basic stuff.
And It's just a way to go for It.
But what If we've more than one <input>
?
Not two... not three... we've more than ten <input>
doing the same stuff?
(it is an exaggeration useful for the post)
As you can see our handleChange
function, changes a specific state in It's setState()
... if we use the same function for other <input>
we will change the value of myFirstState
everytime.
(And trust me... I have seen people use numerous functions doing the same stuff, like these.)
My idea is...
//we've a class... with a more states defined
class App extends Component {
constructor(props){
super(props)
this.state={
myFirstState:"Labrador",
mySecondState:"Akita"
}
//we're going to manage the changes, and setState() equal
//to the user input... for all the possible "keys" in the state object
valueChange = (key) => {
return function (e) {
var obj= {};
state[key] : e.target.value;
this.setState(obj);
}.bind(this);
}
//rendering time...we've more Input tags, with the states as values and one
//function, calling onChange... we're passing the "key" as argument.
render() {
return (
<div className="just a class">
<input placeholder="insertValue" value={this.state.myFirstState}
onChange= {this.valueChange("myFirstState")}/>
<input placeholder="insertValue" value={this.state.mySecondState}
onChange= {this.valueChange("mySecondState")}/>
</div>
)
}
}
With that, we're calling the method setState()
passing an object where the key
is the state we want to change and the value is the user input!.
We're also binding this
or we're going to receive an error.
(Keep in mind... setState()
triggers the render)
I hope I've been useful ... I'm looking for suggestions to manage this kind of case in more efficient ways!
Top comments (19)
Yeah, curried functions are perfect for this. The arrow syntax lends itself to this.
becomes
Or just
valueChange = key => e => this.setState({[key]: e.target.value})
Yesssssssssssssss
Love It!
using curried function is a good idea! it's very useful for handling multiple similar state changes.
another approach, if you're dealing with form elements like inputs etc. would be to use
name
attribute, something like this:but of course it works only with certain html elements (
<input>
,<select>
,<textarea>
among them) and IIRC specification saysname
should be lowercase, although I don't think I've run into any problems with camelCasename
so far.I like this, how about leveraging a
data-
attribute instead ofname
?You're creating a new function for every input you manage for every render pass. This is an anti pattern especially on big state trees. Especially because it will cause re-renders of child components unnecessarily (as the onChange prop for each element changes every render pass. You may want to cache the created functions, or take a different approach
But.. have you seen all the post? _^
I think so, what specifically did I overlook? Supplying a better alternative?
There’s a warning about rerendering... and me asking for suggestions ✌🏻
Sorry if it’s not perfect, I’m here for learning too.
No worries, just wanted to chip in. Somehow dont see a note about rerender, I'm on mobile, perhaps some caching going on.
I like the alternative via name prop for input elements, or a custom data prop, as I wrote in the other comment thread.
Alternatively, I would still create a function property per onChange handler, but create and use a reusable function to limit the repetitiveness to the bare minimum.
You can create a curried function and then memoize it. 😉 It should work! Have a look at Lodash's
curry
andmemoize
functions.You can try this alternative instead that doesn't require you to add any instance method (methods declared using arrow fns).
The approach demonstrated in this post to manage form data is known as controlled components, which is traditional "reactish" way to handle input value changes. Since the post is intended for beginners, maybe you could complement it adding a note to mention this for those who'd like to read further on the subject. 🙂
More details can be found here: reactjs.org/docs/uncontrolled-comp...
In the valueChange function where did you find the state variable. May be it should be obj variable ?
In the second example?
The state is the obj variable.
You can see I’m creating an obj and using key-value pairs in It.
Then I’m passing the object to setState().
you defining
obj
, but then you usestate
. in non-strict mode this leads to the creation of a global variable, in strict mode this leads to an error.After that you use
obj
again, so the new value saved instate
in state isn't even used.Understood!