I create a widget to add and remove comments. Adding works well. And the removal does not work as needed. When rendering, an empty element appears. Although the reducer passes an array of two objects. Please help me figure it out.
DevTools
JS
Use filter instead.
state.filter(cmt => cmt.id !== action.id)
Related
I am trying to hide an element 'GorillaSurfIn' after I click on it.
But also it should fire the 'setShouldGorillaSurfOut' to 'true'. The second part works, but after I added this function:
function hideGorillaSurfIn() {
let element = document.getElementById('gorilla-surf-in');
ReactDOM.findDOMNode(element).style.display =
this.state.isClicked ? 'grid' : 'none';
}
After I click, the code falls apart.
Once I click, the element should be hidden/removed till the next time the App restarts.
Here is the Code Sandbox Link for further explanation.
I am open to any solutions, but also explanations please, as I am still fresh in learning React.
I have changed your code a bit to make it work. You can make further changes according to your need. A few things that I would like to add: -
You should avoid using findDOMNode (in most cases refs can solve your problem) as there are certain drawbacks associated with findDOMNode, such as the react's documentation states "findDOMNode cannot be used with functional components".
I've used refs (forward ref in this case) to make it work.
GorillaSurfIn was called twice, so there were two Gorilla gifs on the screen with same IDs. Not sure if that was the intended behaviour but each element should have unique ID.
Check out the code sandbox.
I am trying to follow an react-course on udemy but am using hooks instead of classes and states as the instructor shows. It is an simple app where I download random userinfo and images and shows them using flash-cards.
Then I need to be able to search/filter the users. I have managed to get this working by using two different useEffects but I would like to know if this is the correct way to solve this. And also if I can get any tips on how to improve my current code.
Project on codesandbox
It's OK. However you don't need to use the second useEffect. you can compute filter directly in the functions body. If you want to cache the results you can use useMemo hook but it's unnecessary here.
Basically what I would do is:
const filter = users && users.length ? users.filter((person) =>
person.name.toLowerCase().includes(searchField.toLowerCase())
); || []
I have created the following demo to help me describe my question: https://codesandbox.io/s/dazzling-https-6ztj2
I have a form where I submit information and store it in a database. On another page, I retrieve this data, and set the checked property for the checkbox accordingly. This part works, in the demo this is represented by the dataFromAPI variable.
Now, the problem is that when I'd like to update the checkboxes, I get all sorts of errors and I don't know how to solve this. The ultimate goal is that I modify the form (either uncheck a checked box or vice versa) and send it off to the database - essentially this is an UPDATE operation, but again that's not visible in the demo.
Any suggestions?
Also note that I have simplified the demo, in the real app I'm working on I have multiple form elements and multiple values in the state.
I recommend you to work with an array of all the id's or whatever you want it to be your list's keys and "map" on the array like here https://reactjs.org/docs/lists-and-keys.html.
It also helps you to control each checkbox element as an item.
Neither your add or delete will work as it is.
Array.push returns the length of the new array, not the new array.
Array.splice returns a new array of the deleted items. And it mutates the original which you shouldn't do. We'll use filter instead.
Change your state setter to this:
// Since we are using the updater form of setState now, we need to persist the event.
e.persist();
setQuestion(prev => ({
...prev,
[e.target.name]: prev.topics.includes(e.target.value)
// Return false to remove the part of the array we don't want anymore
? prev.topics.filter((value) => value != e.target.value)
// Create a new array instead of mutating state
: [...prev.topics, e.target.value]
}));
As regard your example in the codesandbox you can get the expected result using the following snippet
//the idea here is if it exists then remove it otherwise add it to the array.
const handleChange = e => {
let x = data.topics.includes(e.target.value) ? data.topics.filter(item => item !== e.target.value): [...data.topics, e.target.value]
setQuestion({topics:x})
};
So you can get the idea and implement it in your actual application.
I noticed the problem with your code was that you changed the nature of question stored in state which makes it difficult to get the attribute topics when next react re-renders Also you were directly mutating the state. its best to alway use functional array manipulating methods are free from side effects like map, filter and reduce where possible.
I am trying to understand how React works with the new Hooks implementation. In this example, I want the browsers to render selected items as I click on the rendered options. But as you can see, it doesn't work.
Here is the example: https://codesandbox.io/s/pjorxzyrx7
Do I have to use the useEffect in this case? Also, as I understand, useEffect couldn't render anything and only return functions. So, what am I missing here?
Thank you!
You're currently mutating the contents of the selected array instead of replacing it. React can't detect a state change when you do this.
Try something like the following:
const handleSelected = item => {
console.log(item);
console.log(selected);
setSelected([...selected, item]);
};
When updating arrays or objects as a part of a state, always make a new copy to assign so that React can properly know when to re-render.
Also, include relevant parts of your code directly in the question in the future, instead of hiding it behind a link (although including a runnable example is great!)
first I should mention that I'm very new to react so this might be something silly..
I've struggled to get ReactTable's column to be sortable with the help of mattlockyer's gist
What I don't understand is I call setState on columns and then the render call is triggered correctly but it doesn't update the layout.
The render function "columns" contains an updated object with the correct column order, however render does not change the column order nor does sorting columns content.
This is the code in question,
this.setState({
columns: newColLayout,
}, () => {
this.mountEvents();
});
It will trigger a render, but the columns stay the same.
Ive put together a codepen with my current work and with comments about the code in question.
Any help would be greatly appreciated.
OK so i think i figured out whats going on.
The issue is splice modifies the state without triggering a change event, then when the event is fired from setStat, react doesn't see the change made to the column layout as it matches the current value.
The way i get around this is by cloning the column array using slice.
// Clone the current column state.
const columnClone = this.state.columns.slice(0);
// Remove item from array and stick it in a new position.
columnClone.splice(i, 0, columnClone.splice(this.draggedCol, 1)[0]);
Here is the updated code...
Still might be improved by someone who has more experience with react.