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React Class component updates the value for class variable in re-render but not the Function Component

I was playing with ReacJS. I noticed a thing-
In case of Class Component during re-rendering class variable's updated value is updated in screen like:
import React, { Component } from "react";
class Temp extends Component {
constructor(props) {
super(props);
this.count = 0;
this.state = {
foo: 0,
};
}
render() {
return (
<button
onClick={() => {
this.setState({ foo: this.state.foo + 1 });
this.count++;
}}
>
{this.count} - {this.state.foo}
</button>
);
}
}
export default Temp;
But in case of function component the updated value of the ordinary variable is not updated in the screen during re-rendering.
import React, { useRef, useState } from "react";
const RefComponent = () => {
const [stateNumber, setStateNumber] = useState(0);
let refVar = 0;
function incrementAndDelayedLogging() {
setStateNumber(stateNumber + 1);
refVar++;
}
return (
<div>
<button onClick={incrementAndDelayedLogging}>Click</button>
<h4>state: {stateNumber}</h4>
<h4>refVar: {refVar}</h4>
</div>
);
};
export default RefComponent;
Is this how React was implemented or I'm messing around something? I'm curious to know about it.
Thanks

Functional components in React don't have instances, so things like class or instance variables don't necessarily make sense; like others have pointed out in the comments here, React will render (call) functional components and "reset" any local variables that are not explicitly state. Behavior like instance variables for functional components are achieved with useRef.
From the docs:
The useRef() Hook isn’t just for DOM refs. The “ref” object is a generic container whose current property is mutable and can hold any value, similar to an instance property on a class.

This is a consequence of functional components.
Think about it like this: Each time a state var is updated or a prop is updated your function gets called again. All variable declaration will happen again (states are a special case), so let refVar = 0; gets called again.
If you need that variable to live for multiple renders you'll need to declare it in a context that survives re-renders.
You have at least 2 ways of achieving this
declare a state for it with useState
declare it at the module level, but know all your instances of RefComponent will share the same instance

How to modify value passed by props

I'm a begginer in React and would like to figure out how to modify values get using props.
f.e:
I have a MobX GameStore.tsx with #observable values:
export class GameStore {
#observable money = 0;
#observable CPS = 0;
#observable taskCodeLines = 0;
#observable taskCodeLinesTarget = 10;
...
#observable staffFrontEndCount = 4;
#observable staffFrontEndStartCost = 100;
#observable staffPHPCount = 2;
#observable staffPHPStartCost = 250;
}
Now I want to have a few StaffMember objects in Staff class:
render() {
return(
<div className="staff">
<ul className="staff-list">
<StaffMember job="Front End Developer" count={ gameStore.staffFrontEndCount } startCost = { gameStore.staffFrontEndStartCost } />
<StaffMember job="PHP Developer" count={ gameStore.staffPHPCount } startCost = { gameStore.staffPHPStartCost } />
</ul>
</div>
);
}
I pass down a data like name of this objects and some values. And now I want to modify some of them, like:
#observer
export default class StaffMember extends React.Component<any, any> {
#computed get increaseStaffCount() {
return this.props.count;
}
#action hireStaff() {
let cost = this.props.startCost * 1.4 * (this.props.count + 1);
if (gameStore.money >= cost) {
gameStore.money -= cost;
this.props.count += 1; // It's illegal because props data is read-only
this.countCPS();
}
}
How can I do this? Is this OK to create logic like above?
How should I create instances of classes in react and build a generic methods for them?
Thanks for help ;)

React does not allow the modification of props values over the course of a component's life. And there are currently two ways it has gotten around the need to change the value of props.
Load it into a state
Utilize Redux
On the first item, as xSkrappy said before, you can load the props into a Component's state, which can be updated over the course of a component's life, adding this method inside the Component in the following manner:
componentDidMount() {
this.setState({ count: this.props.count })
}
This creates a local state in the component that is equal to the prop value that was passed down to the component from its parent. And you can begin to change it from there.
You can also use the componentWillReceiveProps lifecycle method to re-render the component when the props value changes in its parent component, like such:
componentWillReceiveProps(nextProps) {
if(nextProps.count !== this.props.count) {
this.setState({ count: nextProps.count })
}
}
The second method involves utilizing Redux, a state container that can be used in React applications. Its pattern involves creating a store where the state of the entire application can be managed, and any given component can be connected to that store and receive that state as props.
While utilizing Redux is a lot more complex than the first option given, in the end you are given a lot more freedom because you can make your count value accessible to any component in your application!
Sadly implementing Redux is too lengthy a process to just detail in this answer, so I'll direct you to what I think is a good guide to refactoring your application to use Redux, should you wish to go with this option

The answer to that would be after passing the props inside StaffMember put it inside a state then from there you can modify the state :)

In ReactJs, Props are immutable so you can't modify it. Instead of using Props You can use State. State are mutable you can modify it. Or, you can use Redux concept as per your requirement.
For ex:- First make a state
this.state = {
usersList:[]
};
then you can add modification in your state like this
componentDidMount() {
this.setState({ usersList: this.props.count})
}

Pass properties from parent component to all transcluded children component in Vue

I would like to pass some properties from a parent to all of his children when those are transcluded (content distribution syntax). In this case, the parent doesen't know (as far as I know) his children, so I don't know how to proceed.
More specificly, I want a way to write this :
<my-parent prop1="foo" prop2="bar">
<my-children></my-children> <!-- Must know content of prop1 and prop2 -->
<my-children></my-children> <!-- Must know content of prop1 and prop2 -->
</my-parent>
Instead of having to write this :
<my-parent prop1="foo" prop2="bar">
<my-children prop1="foo" prop2="bar"></my-children>
<my-children prop1="foo" prop2="bar"></my-children>
</my-parent>
Is it possible ? Thanks.

Props allow data flow only one level. If you want to perpetuate data, you can use an event bus instead.
Instantiate an event bus with an empty Vue instance in your main file.
var bus = new Vue();
Then in your parent, emit the event with data to be passed
bus.$emit('myEvent', dataToBePassed);
Listen for myEventanywhere you want to pick up the data. In your case, it is done in your child components
bus.$on('myEvent', function(data) {
.....
});

Here is my solution, that's probably not a great deal, but that's the cleanest solution for what I want to do right now. The principle is to create computed properties that will use own component prop if they exist, or get $parent values otherwise. The real prop would then be accessible in this._prop.
Vue.component('my-children', {
props: ["prop1", "prop2"],
template: "<div>{{_prop1}} - {{_prop2}}</div>",
computed: {
_prop1: function() {
return this.prop1 || this.$parent.prop1;
},
_prop2: function() {
return this.prop2 || this.$parent.prop2;
}
}
});
Here is a mixin generator that does that in a more elegant way, and with, possibly, multiple levels :
function passDown(...passDownProperties) {
const computed = {};
passDownProperties.forEach((prop) => {
computed["_" + prop] = function() {
return this[prop] || this.$parent[prop] || this.$parent["_" + prop];
};
});
return { computed };
}
Vue.component('my-children', {
props: ["prop1", "prop2"],
template: "<div>{{_prop1}} - {{_prop2}}</div>",
mixins: [passDown("prop1", "prop2")]
});

At this point (I'm not a vue expert) I just could think in this solution.
Assign every component's props is boring I agree, so why not doing it programmatically?
// Create a global mixin
Vue.mixin({
mounted() { // each component will execute this function after mounted
if (!this.$children) {
return;
}
for (const child of this.$children) { // iterate each child component
if (child.$options._propKeys) {
for (const propKey of child.$options._propKeys) { // iterate each child's props
// if current component has a property named equal to child prop key
if (Object.prototype.hasOwnProperty.call(this, propKey)) {
// update child prop value
this.$set(child, propKey, this[propKey]);
// create a watch to update value again every time that parent property changes
this.$watch(propKey, (newValue) => {
this.$set(child, propKey, newValue);
});
}
}
}
}
},
});
This works but you will get an ugly vue warn message:
[Vue warn]: Avoid mutating a prop directly since the value will be overwritten whenever the parent component re-renders. Instead, use a data or computed property based on the prop's value.
I'm not sure if this is a good solution but it works, so if you decide to use just keep in mind Global-Mixin recomendations:
Use global mixins sparsely and carefully, because it affects every
single Vue instance created, including third party components.
Please see a full example at https://github.com/aldoromo88/PropsConvention
Hope it helps

How to get a React Component reference to change its class using classList?

I have create a React Component using the following code. In this i am creating tab and added the class and storing its reference to in a global namespace Interface for further processing.
var TabBody = React.createClass({
getInitialState: function() {
return {
class: 'tabBody tab activeTab'
}
},
render: function() {
Interfaces.tabBody = this;
tabSelectionInfo.tabBody = this;
return (
React.createElement('div', {
className: this.state.class,
onClick: handleTabClick
},
React.createElement('span', {}, "Body"))
);
}
});
now using the following function, To add a class to the above component and console is showing an error undefined. how i store the refrance of this component in order to change its class later.
handleTabClick = function() {
Interfaces.tabBody.classList.add('tabPreviewComplete');
}

Above 16.8, using useRef hooks for functional components,
// useRef takes initialValue as param
const fooBarRef = useRef(null);
//DOM Usage
<div className="foo" ref={fooBarRef}>Hello</div>
Usage of reference for useRef after mounting node element,
//Getting node element
const fooBarNode = fooBarRef.current
//Adding class to node element
fooBarNode.classList.add('bar');
Above 16.3, using createRef for class components,
// Creating ref in a constructor
this.fooBarRef = React.createRef();
// DOM usage
<div className="foo" ref={this.fooBarRef}>Hello</div>
Usage of reference for createRef after mounting node element,
//Getting node element
const fooBarNode = this.fooBarRef.current
//Adding class to node element
fooBarNode.classList.add('bar');
Below 16.3, using callBackRef,
// Creating ref in a constructor
this.fooBarRef = null;
this.setFooBarRef = (ref) => {
this.fooBarRef = ref;
}
// DOM usage
<div className="foo" ref={this.setFooBarRef}>Hello</div>
Usage of reference after mounting node element,
//Adding class name
this.fooBarRef.classList.add('bar');

That's because this is the reference to your class instance, not a DOM element. To access DOM elements (since React uses a virtual DOM) you need to create a reference, i.e:
React.createElement('div', {
ref: 'tabBody'
You can then access it via this.refs.tabBody
You shouldn't pass this reference outside of the class however. Instead you can pass the reference to handleTabClick when the event happens:
React.createElement('div', {
ref: 'tabBody'
onClick: e => this.props.handleTabClick(e, this.refs.tabBody)
Then you can do:
handleTabClick = function(e, tabBody) {
tabBody.classList.add('tabPreviewComplete');
}
Personally I would change the state though, so that if the component re-renders it has the correct class.
Fiddle: http://jsfiddle.net/ferahl/dpvb1h3y/

As you have specified in your code that your class name is used using a state variable named 'class' containing the value 'tabBody tab activeTab'
className: this.state.class,
Thats why you must have to use setState() method to change your className. As you have the reference to your class instance in global namespace named 'Interface.tabBody' which can be used to set your className by calling setState() e.g
Interface.tabBody.setState({class: 'tabBody tab activeTab disabled'});
This method is used when you want to access class instance outside of the React.
if you are using handleclick() in your react then you can use the following code
handleTabClick = function() {
this.setState({class: 'tabBody tab activeTab disabled'});
}
By calling setState() the React will detect changes and re-renders component.

Pass props to parent component in React.js

Is there not a simple way to pass a child's props to its parent using events, in React.js?
var Child = React.createClass({
render: function() {
<a onClick={this.props.onClick}>Click me</a>
}
});
var Parent = React.createClass({
onClick: function(event) {
// event.component.props ?why is this not available?
},
render: function() {
<Child onClick={this.onClick} />
}
});
I know you can use controlled components to pass an input's value but it'd be nice to pass the whole kit n' kaboodle. Sometimes the child component contains a set of information you'd rather not have to look up.
Perhaps there's a way to bind the component to the event?
UPDATE – 9/1/2015
After using React for over a year, and spurred on by Sebastien Lorber's answer, I've concluded passing child components as arguments to functions in parents is not in fact the React way, nor was it ever a good idea. I've switched the answer.

Edit: see the end examples for ES6 updated examples.
This answer simply handle the case of direct parent-child relationship. When parent and child have potentially a lot of intermediaries, check this answer.
Other solutions are missing the point
While they still work fine, other answers are missing something very important.
Is there not a simple way to pass a child's props to its parent using events, in React.js?
The parent already has that child prop!: if the child has a prop, then it is because its parent provided that prop to the child! Why do you want the child to pass back the prop to the parent, while the parent obviously already has that prop?
Better implementation
Child: it really does not have to be more complicated than that.
var Child = React.createClass({
render: function () {
return <button onClick={this.props.onClick}>{this.props.text}</button>;
},
});
Parent with single child: using the value it passes to the child
var Parent = React.createClass({
getInitialState: function() {
return {childText: "Click me! (parent prop)"};
},
render: function () {
return (
<Child onClick={this.handleChildClick} text={this.state.childText}/>
);
},
handleChildClick: function(event) {
// You can access the prop you pass to the children
// because you already have it!
// Here you have it in state but it could also be
// in props, coming from another parent.
alert("The Child button text is: " + this.state.childText);
// You can also access the target of the click here
// if you want to do some magic stuff
alert("The Child HTML is: " + event.target.outerHTML);
}
});
JsFiddle
Parent with list of children: you still have everything you need on the parent and don't need to make the child more complicated.
var Parent = React.createClass({
getInitialState: function() {
return {childrenData: [
{childText: "Click me 1!", childNumber: 1},
{childText: "Click me 2!", childNumber: 2}
]};
},
render: function () {
var children = this.state.childrenData.map(function(childData,childIndex) {
return <Child onClick={this.handleChildClick.bind(null,childData)} text={childData.childText}/>;
}.bind(this));
return <div>{children}</div>;
},
handleChildClick: function(childData,event) {
alert("The Child button data is: " + childData.childText + " - " + childData.childNumber);
alert("The Child HTML is: " + event.target.outerHTML);
}
});
JsFiddle
It is also possible to use this.handleChildClick.bind(null,childIndex) and then use this.state.childrenData[childIndex]
Note we are binding with a null context because otherwise React issues a warning related to its autobinding system. Using null means you don't want to change the function context. See also.
About encapsulation and coupling in other answers
This is for me a bad idea in term of coupling and encapsulation:
var Parent = React.createClass({
handleClick: function(childComponent) {
// using childComponent.props
// using childComponent.refs.button
// or anything else using childComponent
},
render: function() {
<Child onClick={this.handleClick} />
}
});
Using props:
As I explained above, you already have the props in the parent so it's useless to pass the whole child component to access props.
Using refs:
You already have the click target in the event, and in most case this is enough.
Additionnally, you could have used a ref directly on the child:
<Child ref="theChild" .../>
And access the DOM node in the parent with
React.findDOMNode(this.refs.theChild)
For more advanced cases where you want to access multiple refs of the child in the parent, the child could pass all the dom nodes directly in the callback.
The component has an interface (props) and the parent should not assume anything about the inner working of the child, including its inner DOM structure or which DOM nodes it declares refs for. A parent using a ref of a child means that you tightly couple the 2 components.
To illustrate the issue, I'll take this quote about the Shadow DOM, that is used inside browsers to render things like sliders, scrollbars, video players...:
They created a boundary between what you, the Web developer can reach
and what’s considered implementation details, thus inaccessible to
you. The browser however, can traipse across this boundary at will.
With this boundary in place, they were able to build all HTML elements
using the same good-old Web technologies, out of the divs and spans
just like you would.
The problem is that if you let the child implementation details leak into the parent, you make it very hard to refactor the child without affecting the parent. This means as a library author (or as a browser editor with Shadow DOM) this is very dangerous because you let the client access too much, making it very hard to upgrade code without breaking retrocompatibility.
If Chrome had implemented its scrollbar letting the client access the inner dom nodes of that scrollbar, this means that the client may have the possibility to simply break that scrollbar, and that apps would break more easily when Chrome perform its auto-update after refactoring the scrollbar... Instead, they only give access to some safe things like customizing some parts of the scrollbar with CSS.
About using anything else
Passing the whole component in the callback is dangerous and may lead novice developers to do very weird things like calling childComponent.setState(...) or childComponent.forceUpdate(), or assigning it new variables, inside the parent, making the whole app much harder to reason about.
Edit: ES6 examples
As many people now use ES6, here are the same examples for ES6 syntax
The child can be very simple:
const Child = ({
onClick,
text
}) => (
<button onClick={onClick}>
{text}
</button>
)
The parent can be either a class (and it can eventually manage the state itself, but I'm passing it as props here:
class Parent1 extends React.Component {
handleChildClick(childData,event) {
alert("The Child button data is: " + childData.childText + " - " + childData.childNumber);
alert("The Child HTML is: " + event.target.outerHTML);
}
render() {
return (
<div>
{this.props.childrenData.map(child => (
<Child
key={child.childNumber}
text={child.childText}
onClick={e => this.handleChildClick(child,e)}
/>
))}
</div>
);
}
}
But it can also be simplified if it does not need to manage state:
const Parent2 = ({childrenData}) => (
<div>
{childrenData.map(child => (
<Child
key={child.childNumber}
text={child.childText}
onClick={e => {
alert("The Child button data is: " + child.childText + " - " + child.childNumber);
alert("The Child HTML is: " + e.target.outerHTML);
}}
/>
))}
</div>
)
JsFiddle
PERF WARNING (apply to ES5/ES6): if you are using PureComponent or shouldComponentUpdate, the above implementations will not be optimized by default because using onClick={e => doSomething()}, or binding directly during the render phase, because it will create a new function everytime the parent renders. If this is a perf bottleneck in your app, you can pass the data to the children, and reinject it inside "stable" callback (set on the parent class, and binded to this in class constructor) so that PureComponent optimization can kick in, or you can implement your own shouldComponentUpdate and ignore the callback in the props comparison check.
You can also use Recompose library, which provide higher order components to achieve fine-tuned optimisations:
// A component that is expensive to render
const ExpensiveComponent = ({ propA, propB }) => {...}
// Optimized version of same component, using shallow comparison of props
// Same effect as React's PureRenderMixin
const OptimizedComponent = pure(ExpensiveComponent)
// Even more optimized: only updates if specific prop keys have changed
const HyperOptimizedComponent = onlyUpdateForKeys(['propA', 'propB'])(ExpensiveComponent)
In this case you could optimize the Child component by using:
const OptimizedChild = onlyUpdateForKeys(['text'])(Child)

Update (9/1/15): The OP has made this question a bit of a moving target. It’s been updated again. So, I feel responsible to update my reply.
First, an answer to your provided example:
Yes, this is possible.
You can solve this by updating Child’s onClick to be this.props.onClick.bind(null, this):
var Child = React.createClass({
render: function () {
return <a onClick={this.props.onClick.bind(null, this)}>Click me</a>;
}
});
The event handler in your Parent can then access the component and event like so:
onClick: function (component, event) {
// console.log(component, event);
},
JSBin snapshot
But the question itself is misleading
Parent already knows Child’s props.
This isn’t clear in the provided example because no props are actually being provided. This sample code might better support the question being asked:
var Child = React.createClass({
render: function () {
return <a onClick={this.props.onClick}> {this.props.text} </a>;
}
});
var Parent = React.createClass({
getInitialState: function () {
return { text: "Click here" };
},
onClick: function (event) {
// event.component.props ?why is this not available?
},
render: function() {
return <Child onClick={this.onClick} text={this.state.text} />;
}
});
It becomes much clearer in this example that you already know what the props of Child are.
JSBin snapshot
If it’s truly about using a Child’s props…
If it’s truly about using a Child’s props, you can avoid any hookup with Child altogether.
JSX has a spread attributes API I often use on components like Child. It takes all the props and applies them to a component. Child would look like this:
var Child = React.createClass({
render: function () {
return <a {...this.props}> {this.props.text} </a>;
}
});
Allowing you to use the values directly in the Parent:
var Parent = React.createClass({
getInitialState: function () {
return { text: "Click here" };
},
onClick: function (text) {
alert(text);
},
render: function() {
return <Child onClick={this.onClick.bind(null, this.state.text)} text={this.state.text} />;
}
});
JSBin snapshot
And there's no additional configuration required as you hookup additional Child components
var Parent = React.createClass({
getInitialState: function () {
return {
text: "Click here",
text2: "No, Click here",
};
},
onClick: function (text) {
alert(text);
},
render: function() {
return <div>
<Child onClick={this.onClick.bind(null, this.state.text)} text={this.state.text} />
<Child onClick={this.onClick.bind(null, this.state.text2)} text={this.state.text2} />
</div>;
}
});
JSBin snapshot
But I suspect that’s not your actual use case. So let’s dig further…
A robust practical example
The generic nature of the provided example is a hard to talk about. I’ve created a component that demonstrations a practical use for the question above, implemented in a very Reacty way:
DTServiceCalculator working example
DTServiceCalculator repo
This component is a simple service calculator. You provide it with a list of services (with names and prices) and it will calculate a total the selected prices.
Children are blissfully ignorant
ServiceItem is the child-component in this example. It doesn’t have many opinions about the outside world. It requires a few props, one of which is a function to be called when clicked.
<div onClick={this.props.handleClick.bind(this.props.index)} />
It does nothing but to call the provided handleClick callback with the provided index[source].
Parents are Children
DTServicesCalculator is the parent-component is this example. It’s also a child. Let’s look.
DTServiceCalculator creates a list of child-component (ServiceItems) and provides them with props [source]. It’s the parent-component of ServiceItem but it`s the child-component of the component passing it the list. It doesn't own the data. So it again delegates handling of the component to its parent-component source
<ServiceItem chosen={chosen} index={i} key={id} price={price} name={name} onSelect={this.props.handleServiceItem} />
handleServiceItem captures the index, passed from the child, and provides it to its parent [source]
handleServiceClick (index) {
this.props.onSelect(index);
}
Owners know everything
The concept of “Ownership” is an important one in React. I recommend reading more about it here.
In the example I’ve shown, I keep delegating handling of an event up the component tree until we get to the component that owns the state.
When we finally get there, we handle the state selection/deselection like so [source]:
handleSelect (index) {
let services = […this.state.services];
services[index].chosen = (services[index].chosen) ? false : true;
this.setState({ services: services });
}
Conclusion
Try keeping your outer-most components as opaque as possible. Strive to make sure that they have very few preferences about how a parent-component might choose to implement them.
Keep aware of who owns the data you are manipulating. In most cases, you will need to delegate event handling up the tree to the component that owns that state.
Aside: The Flux pattern is a good way to reduce this type of necessary hookup in apps.

It appears there's a simple answer. Consider this:
var Child = React.createClass({
render: function() {
<a onClick={this.props.onClick.bind(null, this)}>Click me</a>
}
});
var Parent = React.createClass({
onClick: function(component, event) {
component.props // #=> {Object...}
},
render: function() {
<Child onClick={this.onClick} />
}
});
The key is calling bind(null, this) on the this.props.onClick event, passed from the parent. Now, the onClick function accepts arguments component, AND event. I think that's the best of all worlds.
UPDATE: 9/1/2015
This was a bad idea: letting child implementation details leak in to the parent was never a good path. See Sebastien Lorber's answer.

The question is how to pass argument from child to parent component. This example is easy to use and tested:
//Child component
class Child extends React.Component {
render() {
var handleToUpdate = this.props.handleToUpdate;
return (<div><button onClick={() => handleToUpdate('someVar')}>Push me</button></div>
)
}
}
//Parent component
class Parent extends React.Component {
constructor(props) {
super(props);
var handleToUpdate = this.handleToUpdate.bind(this);
}
handleToUpdate(someArg){
alert('We pass argument from Child to Parent: \n' + someArg);
}
render() {
var handleToUpdate = this.handleToUpdate;
return (<div>
<Child handleToUpdate = {handleToUpdate.bind(this)} />
</div>)
}
}
if(document.querySelector("#demo")){
ReactDOM.render(
<Parent />,
document.querySelector("#demo")
);
}
Look at JSFIDDLE

Basically you use props to send information to and from Child and Parent.
Adding to all the wonderful answers, let me give a simple example that explains passing values from child to parent component in React
App.js
class App extends React.Component {
constructor(){
super();
this.handleFilterUpdate = this.handleFilterUpdate.bind(this);
this.state={name:'igi'}
}
handleFilterUpdate(filterValue) {
this.setState({
name: filterValue
});
}
render() {
return (
<div>
<Header change={this.handleFilterUpdate} name={this.state.name} />
<p>{this.state.name}</p>
</div>
);
}
}
Header.js
class Header extends React.Component {
constructor(){
super();
this.state={
names: 'jessy'
}
}
Change(event) {
// this.props.change(this.state.names);
this.props.change('jessy');
}
render() {
return (
<button onClick={this.Change.bind(this)}>click</button>
);
}
}
Main.js
import React from 'react';
import ReactDOM from 'react-dom';
import App from './App.jsx';
ReactDOM.render(<App />, document.getElementById('app'));
Thats it , now you can pass values from your client to the server.
Take a look at the Change function in the Header.js
Change(event) {
// this.props.change(this.state.names);
this.props.change('jessy');
}
This is how you push values into the props from client to the server

Here is a simple 3 step ES6 implementation using function binding in the parent constructor. This is the first way the official react tutorial recommends (there is also public class fields syntax not covered here). You can find all of this information here https://reactjs.org/docs/handling-events.html
Binding Parent Functions so Children Can Call Them (And pass data up to the parent! :D )
Make sure in the parent constructor you bind the function you created in the parent
Pass the bound function down to the child as a prop (No lambda because we are passing a ref to function)
Call the bound function from a child event (Lambda! We're calling the function when the event is fired.
If we don't do this the function will automatically run on load and not be triggered on the event.)
Parent Function
handleFilterApply(filterVals){}
Parent Constructor
this.handleFilterApply = this.handleFilterApply.bind(this);
Prop Passed to Child
onApplyClick = {this.handleFilterApply}
Child Event Call
onClick = {() => {props.onApplyClick(filterVals)}

This is an example without using the onClick event. I simply pass a callback function to the child by props. With that callback the child call also send data back. I was inspired by the examples in the docs.
Small example (this is in a tsx files, so props and states must be declared fully, I deleted some logic out of the components, so it is less code).
*Update: Important is to bind this to the callback, otherwise the callback has the scope of the child and not the parent. Only problem: it is the "old" parent...
SymptomChoser is the parent:
interface SymptomChooserState {
// true when a symptom was pressed can now add more detail
isInDetailMode: boolean
// since when user has this symptoms
sinceDate: Date,
}
class SymptomChooser extends Component<{}, SymptomChooserState> {
state = {
isInDetailMode: false,
sinceDate: new Date()
}
helloParent(symptom: Symptom) {
console.log("This is parent of: ", symptom.props.name);
// TODO enable detail mode
}
render() {
return (
<View>
<Symptom name='Fieber' callback={this.helloParent.bind(this)} />
</View>
);
}
}
Symptom is the child (in the props of the child I declared the callback function, in the function selectedSymptom the callback is called):
interface SymptomProps {
// name of the symptom
name: string,
// callback to notify SymptomChooser about selected Symptom.
callback: (symptom: Symptom) => void
}
class Symptom extends Component<SymptomProps, SymptomState>{
state = {
isSelected: false,
severity: 0
}
selectedSymptom() {
this.setState({ isSelected: true });
this.props.callback(this);
}
render() {
return (
// symptom is not selected
<Button
style={[AppStyle.button]}
onPress={this.selectedSymptom.bind(this)}>
<Text style={[AppStyle.textButton]}>{this.props.name}</Text>
</Button>
);
}
}