just a quick query.
I have an array of data points and using this to create instances of a component.
The parent component that creates an array of children components also have some functions I wish to hand down to its children. Is there any way this is possible? Check the code and let me know, I am getting errors.
class App extends React.Component {
constructor(props) {
super(props)
this.handleNext = this.handleNext.bind(this)
}
handleNext() {
// some function that uses setState and will cause component to re render
}
render() {
let children = someArray.map(function(elem, index) {
return (
<ChildComponent name = {elem.name} handDownFunc = {this.handleNext}/>
)
})
return (
{children} // I want them to each be able to access and use handleNext
)
}
}
You got this error, because using function keyword instead of arrow function.
For more infromation please follow this link.
So, it will be someArray.map(() => { return() })
Related
This is the first project I'm building in react so i apologise for any errors.
I have three components in React. The method is declared in the top level with two parameters. I pass this method to a child component. In this component I want to call the method inside a map, using the index of the map as an argument. Here is the code:
class App extends Component {
constructor() {
super();
this.state = {
workExperience: [
{ points: [{id: 1, point: "firstPoint"}, {id: 2, point: "secondPoint"}]
]
}
this.captureTask = this.captureTask.bind(this);
}
captureTask(e, index){
//clone state, want to access array using map index in child component below and capture value of the input to update this state
clonedState.points[index] = e.target.value
console.log(index) //undefined
}
render(){
return(
<ChildComponent captureTask={(e, index) => this.captureTask(e, index)} />
)
}
class ChildComponent extends Component {
constructor(props){
super()
}
render(){
return(
<div>
{this.props.points.map((point, index) => {
return <Input key={point.id} handleChange={(e, index) => this.props.captureTask(e, index)} />
})}
</div>
)
}
My issue is in the captureTask method. The index value returns undefined when it gets back to the function. However within the Map I'm able to log index value without any issue.
Is there something I should be doing differently in order to be able to use the map index as an argument in a parent method?
Thanks for any help.
Change the handleChange prop to the following:
handleChange = { (e) => this.props.captureTask(e, index) }
i.e. Remove the index from the arguments list of the arrow function.
I've imported a custom component into my screen and rendered it in the render() function. Then, created a ref to that custom component. Now, the render() function simply looks like this.
render() {
return (
<View>
<MyComponent ref={component => this.myComponent = component} />
</View>
)
}
Then, I've created another function to access the state of my custom component. I wrote it like this.
myFunction = (ref) => {
ref.setState({ myState: myValue })
}
Then, I called that function like this.
this.myFunction(this.myComponent)
But, it does not work. It gives me the following error.
null is not an object (evaluating 'ref.setState')
Actually what I need this myFunction to do is,
this.myComponent.setState({ myState: myValue })
Can you please help me to solve this problem?
ref is not your this object. it's dom for your componnet. For setState you need this of your component.
you can pass this as argument.
myFunction(this)
Now you will be able to do ref.setState in myFunction.
function myFunction(ref) {
ref.setState({ myState: myValue })
}
To use setState, just use your component's context (this keyword). The context also have your ref in it, so you don't need to pass it as an argument if you are inside one component(not forwarding down to children)
myFunction = (event) => {
this.myComponent // -> points to your ref, DOM element
this.setState() // use your setState like that
}
Don't forget to bind your context in parent component if you want to pass the handler to the child components. Refer to this useful topic
EDIT: Based on your comment, I guess you want to update the parent state by calling a handler in some other component. To do that, you need to create a handler in your parent component, bind the context and pass it as a property to the child component. Next up, you need to assign this handler in your child component. You cannot pass a context with setState method via argument or ref, this is just not how it works in javascript and in react.
Example:
// ParentComponent.js
class ParentComponent extends React.Component {
constructor(props) {
super(props);
this.state = {
value: 1,
};
this.onChangeHandler = this.onChangeHandler.bind(this);
}
onChangeHandler(event) {
this.setState({
value: someNewValue // will update state on parent component
})
}
render() {
return (
<View>
<SomeComponent>{this.state.value}</SomeComponent>
<ChildrenComponent onChangeHandler={this.onChangeHandler} />
</View>
);
}
}
// ChildrenComponent.js
const ChildrenComponent = (props) => (
<View>
<Button
onPress={props.onChangeHandler}
title="click me to change parent state"
/>
</View>
);
Hopefully, this is what you need :)
I am working to build a Pokedex from JSON data in React. I am refactoring this project from one I built in jQuery, so it could be that the jQuery approach is causing me to misunderstand how to approach this problem with proper React thinking. What's tripping me up so far is how to dynamically render multiple child elements based on the JSON I pass from a the parent element (this would be jQuery append).
Here is my App.js code:
class App extends Component {
render() {
return (
<div className="App background">
<div className="content">
<Header />
<TilesContainer pokedexName="national"/>
</div>
</div>
);
}
The TilesContainer essentially receives the name of a Pokedex and makes a call to an API. The individual Pokemon names are stored in an array in the TilesContainer state (this.state.pokemon), as below.
class TilesContainer extends Component {
constructor(props){
super(props);
this.state = {pokemon: []};
this.getPokemon = this.getPokemon.bind(this);
this.tiles = this.tiles.bind(this);
}
getPokemon() {
// set this.state.pokemon to the list
let link = 'https://pokeapi.co/api/v2/pokedex/' + this.props.pokedexName + '/';
fetch(link)
.then(response => response.json())
.then(myJson => {
let list = myJson['pokemon_entries'];
list.forEach(pokemon => {
this.state.pokemon.push(pokemon);
})
})
this.tiles();
}
tiles() {
if (this.state.pokemon.length > 0) {
return (
this.state.pokemon.map(pokemon => {
<Tile number={pokemon.entry_number}/>
})
)
}
}
render(){
this.getPokemon();
return (
<div id="tiles-container"
className="tiles-container">
<h1>TilesContainer Test</h1>
<Tile number={1} />
</div>
)
}
}
export default TilesContainer
Again, the idea is that a Pokemon tile is render for each Pokemon in the Pokedex JSON (which for now I've stored in this.state.pokemon - not sure if this is the best approach). I found an example here on Stack Overflow that uses an additional function (this this case this.tiles() to generate what I think is an array of returns with different child elements). The <Tile number={1} /> is a hardcoded example of how the tile is called.
Currently no dynamically-rendered tiles show up when the code runs. Is this the correct approach. I'd really appreciate any suggestions.
Thanks!
It looks like you're almost there.
First off, never modify state directly. Use this.setState() instead. State in React is updated asynchronously. For your purposes, you should be able to modify getPokemon() like the following. I also removed the this.tiles() call, as it is unnecessary.
getPokemon() {
// set this.state.pokemon to the list
let link = 'https://pokeapi.co/api/v2/pokedex/' + this.props.pokedexName + '/';
fetch(link)
.then(response => response.json())
.then(myJson => {
let list = myJson['pokemon_entries'];
this.setState({
pokemon: list,
});
})
}
A minor correction for tiles(): when using an arrow function and returning something in one line, use parentheses instead of curly braces. When you use curly braces, you have to include a return statement. With parentheses, you do not.
tiles() {
if (this.state.pokemon.length > 0) {
return (
this.state.pokemon.map(pokemon => (
<Tile number={pokemon.entry_number}/>
))
)
}
}
Next, since tiles() returns your dynamic tile components, it needs to be included in what you return in render().
render(){
return (
<div id="tiles-container"
className="tiles-container"
>
<h1>TilesContainer Test</h1>
{this.tiles()}
</div>
)
}
Lastly, I think the call to this.getPokemon() would make more sense in the constructor, rather than in render().
I think your method of getting the json data and storing it in state is fine, by the way. In the future, you may want to look into Redux to manage your state, but it could be overkill for a really small application.
so you are passing the pokedexName from the parent component which is app.js, once you get the props you can call the rest api call on the componentWillMount life cycle.
so on the render since the api call has been initiated it wont have any data thats why we are using a ternary operator to check the array once the api call get finished and we get the data we are setting the data to the pokemon array.
Since the state is updated react will automatically render a re render so the data will appear.
i hope the below code will solve the issue, please let me know :)
// App.js
import React, { Component } from 'react';
import TilesContainer from './components/TileContainer/TilesContainer'
class App extends Component {
render() {
return (
<div>
<TilesContainer pokedexName="national" />
</div>
);
}
}
export default App;
// Tiles container
import React, {Component} from 'react';
import axios from 'axios';
class TilesContainer extends Component{
//state
state ={
pokemon: []
}
// life cycle methods
componentWillMount(){
let link = 'https://pokeapi.co/api/v2/pokedex/' + this.props.pokedexName + '/';
axios.get(link)
.then(res => {
this.setState({
pokemon: res.data["pokemon_entries"]
})
})
}
render(){
let style ={display:"inline"}
return(
<div>
{
this.state.pokemon.length > 0 ?
this.state.pokemon.map(pokemon => {
return(
<div key={pokemon.entry_number}>
<p style={style}>{pokemon.entry_number}</p>
<a href={pokemon.pokemon_species.url}>{pokemon.pokemon_species.name}</a>
</div>
)
})
:
null
}
</div>
)
}
}
export default TilesContainer
I have a react component that I wish to populate with images using the Dropbox api. The api part works fine, but the component is rendered before the data comes through & so the array is empty. How can I delay the rendering of the component until it has the data it needs?
var fileList = [];
var images = [];
var imageSource = [];
class Foo extends React.Component {
render(){
dbx.filesListFolder({path: ''})
.then(function(response) {
fileList=response.entries;
for(var i=0; i<fileList.length; i++){
imageSource.push(fileList[0].path_lower);
}
console.log(imageSource);
})
for(var a=0; a<imageSource.length; a++){
images.push(<img key={a} className='images'/>);
}
return (
<div className="folioWrapper">
{images}
</div>
);
}
}
Thanks for your help!
Changes:
1. Don't do the api call inside render method, use componentDidMount lifecycle method for that.
componentDidMount:
componentDidMount() is invoked immediately after a component is
mounted. Initialization that requires DOM nodes should go here. If you
need to load data from a remote endpoint, this is a good place to
instantiate the network request. Setting state in this method will
trigger a re-rendering.
2. Define the imageSource variable in state array with initial value [], once you get the response update that using setState, it will automatically re-render the component with updated data.
3. Use the state array to generate the ui components in render method.
4. To hold the rendering until you didn't get the data, put the condition inside render method check the length of imageSource array if length is zero then return null.
Write it like this:
class Foo extends React.Component {
constructor(){
super();
this.state = {
imageSource: []
}
}
componentDidMount(){
dbx.filesListFolder({path: ''})
.then((response) => {
let fileList = response.entries;
this.setState({
imageSource: fileList
});
})
}
render(){
if(!this.state.imageSource.length)
return null;
let images = this.state.imageSource.map((el, i) => (
<img key={i} className='images' src={el.path_lower} />
))
return (
<div className="folioWrapper">
{images}
</div>
);
}
}
You should be using your component's state or props so that it will re-render when data is updated. The call to Dropbox should be done outside of the render method or else you'll be hitting the API every time the component re-renders. Here's an example of what you could do.
class Foo extends React.Component {
constructor(props) {
super(props);
this.state = {
imageSource: []
}
}
componentDidMount() {
dbx.filesListFolder({ path: '' }).then(function(response) {
const fileList = response.entries;
this.setState({
imageSource: fileList.map(file => file.path_lower);
})
});
}
render() {
return (
<div className="folioWrapper">
{this.state.imageSource.map((image, i) => <img key={i} className="images" src={image} />)}
</div>
);
}
}
If there are no images yet, it'll just render an empty div this way.
First off, you should be using the component's state and not using globally defined variables.
So to avoid showing the component with an empty array of images, you'll need to apply a conditional "loading" class on the component and remove it when the array is no longer empty.
I'm new to React.JS and trying to create a click event on an element inside a rendered component.
Here is my code:
class InputPanel extends React.Component{
handleClick(i,j) {
this.props.dispatch(actions.someMethod());
// e.preventDefault();
}
render() {
const { dispatch, board } = this.props;
return(
<div>
{
board.map((row, i) => (
<div>{row.map((cell, j) => <div className="digit"
onClick={this.handleClick(i,j)}>{cell}</div>)}</div>
))
}
</div>
);
}
};
My problem is that "handleClick" gets triggered after page load without any mouse clicked!
I've read about React.JS lifecycle and thought about registering to click event in componentDidMount method, but i'm really not sure about it:
Is there any easier way ? (or: Am I doing something wrong that triggers click ?)
If adding componentDidMount method is the right way - how can I get the element I create in render method ?
You should not use .bind when passing the callback as a prop. There’s a ESLint rule for that. You can read more about how to pass callback without breaking React performance here.
Summary:
make sure you aren’t calling functions but pass functions as handlers in your props.
make sure you do not create functions on every render, for that, you need to bind your handlers in parent component, pass correct the required data (such as indices of iteration) down the child component and have it call the parent’s handler with the data it has
Ideally you’d create another component for the rows and pass the callback there. Moreover, ideally you’d bind the onClick in the parent component’s constructor (or componentWillMount). Otherwise every time render runs a new function is created (in both anonymous function handler () => { this.onClick() } and this.onClick.bind and defeat React’s vdom diff causing every row to rerender every time.
So:
class InputPanel extends React.Component{
constructor() {
super();
this.handleClick = this.handleClick.bind(this);
}
handleClick(i,j) {
this.props.dispatch(actions.someMethod());
// e.preventDefault();
}
render() {
const { dispatch, board } = this.props;
return(
<div>
{board.map((row, i) => <div>
{row.map((cell, j) => <Digit
onClick={this.handleClick})
i={i}
j={j}
cell={cell}
/>)}
</div>)}
</div>
);
}
};
class Digit extends React.Component {
constructor() {
super();
this.handleClick = this.handleClick.bind(this);
}
handleClick() {
this.props.onClick(this.props.i, this.props.j);
}
render() {
return <div
className="digit"
onClick={this.handleClick}
>{this.props.cell}</div>
}
}
It is because you are calling this.handleClick() function instead of providing a function definition as onClick prop.
Try changing the div line like this:
<div className="digit" onClick={ () => this.handleClick(i,j) }>{cell}</div>
Also you have to bind this.handleClick() function. You can add a constructor and bind all the member functions of a class there. that's the best practice in ES6.
constructor(props, context) {
super(props, context);
this.handleClick = this.handleClick.bind(this);
}
You call this function in render. You should only transfer function and bind params.
onClick={this.handleClick.bind(null,i,j)}
You should use .bind().
class InputPanel extends React.Component{
handleClick(i,j) {
this.props.dispatch(actions.someMethod());
// e.preventDefault();
}
render() {
const { dispatch, board } = this.props;
return(
<div>
{
board.map((row, i) => (
<div>{row.map((cell, j) => <div className="digit"
onClick={this.handleClick.bind(null,i,j)}>{cell}</div>)}</div>
))
}
</div>
);
}
};