Phosphenes

This Clock component receives two props: color and time. When you select a different color in the select box, the Clock component receives a different color prop from its parent component. However, for some reason, the displayed color doesn’t update. Why? Fix the problem.

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If your state variable is an object, remember that you can’t update only one field in it without explicitly copying the other fields. For example, you can’t do setPosition({ x: 100 }) in the above example because it would not have the y property at all! Instead, if you wanted to set x alone, you would either do setPosition({ ...position, x: 100 }), or split them into two state variables and do setX(100).

You can nest state as much as you like, but making it “flat” can solve numerous problems. It makes state easier to update, and it helps ensure you don’t have duplication in different parts of a nested object.

Why do I see flashing lights when I close my eyes to sleep Reddit

A community for those with Temporal Light Modulation (rapid pulsing light flicker) sensitivity. PWM, a common screen dimming techniques today, aggravates its provocative flicker by up to 6300%. Symptoms experienced among sensitive users include: eyestrain; headache; migraine. A new screen pulsing dimming technique introduced, called PAM, equally aggravates (to a slightly lesser extent). Do refer to the 'Background of Community' section to learn more about the above phenomenon.

Why do I seestrobelights when I close my eyes

The distance from the principal focus to the center of the lens is the focal length of the lens; the focal length is positive for a converging lens and negative ...

The goal behind these principles is to make state easy to update without introducing mistakes. Removing redundant and duplicate data from state helps ensure that all its pieces stay in sync. This is similar to how a database engineer might want to “normalize” the database structure to reduce the chance of bugs. To paraphrase Albert Einstein, “Make your state as simple as it can be—but no simpler.”

Here, a color state variable is initialized to the messageColor prop. The problem is that if the parent component passes a different value of messageColor later (for example, 'red' instead of 'blue'), the color state variable would not be updated! The state is only initialized during the first render.

why am i seeing flashes oflightin the corner of my eye?

Imagine a travel plan consisting of planets, continents, and countries. You might be tempted to structure its state using nested objects and arrays, like in this example:

Structuring state well can make a difference between a component that is pleasant to modify and debug, and one that is a constant source of bugs. Here are some tips you should consider when structuring state.

As a result, the change handlers don’t need to do anything special to update it. When you call setFirstName or setLastName, you trigger a re-render, and then the next fullName will be calculated from the fresh data.

It last for just a couple of minutes and decreases in intensity gradually over that time, assuming I've turned the phone off and am in complete darkness.

202018 — Two of the most common focal lengths for true macro lenses are 50mm and 100mm. The 50mm macro lenses are often smaller and faster than 100mm ...

Why do I see flashing lights when I close my eyes to sleep

I have an iPhone 14 Pro Max and it happens even after just looking at the screen while surrounded with darkness for only a minute. The longer I use the phone in this situation the stronger and brighter the strobe lighting effects are. I decided a while back that I probably wasn't sensitive to it because my chronic headaches were still there even if I went 2 weeks with no screen usage. However, the strobe lighting does concern me and what it might be doing to my eyes and neurological aspects.

Can high blood pressure cause flashing lights in eyes

Flickeringvisionin lowlight

Microscope cameras, microscope to camera adapters, microscopes, software, macro photography, stereo support stands, and complete imaging systems for ...

Technically, you can use either of these approaches. But if some two state variables always change together, it might be a good idea to unify them into a single state variable. Then you won’t forget to always keep them in sync, like in this example where moving the cursor updates both coordinates of the red dot:

Does anyone else see/get strobe lighting effects (fast flashing white light) in their eyes/vision after using their phone with PWM in darkness?

Lightning AI, San Francisco, California. 150 likes · 6 were here. Lightning AI is an artificial intelligence marketing platform that automates &...

Based of the research, crown glass has a refractive index in the range of 1.5 to 1.6. Justin Che -- 2005

Another case where you’ll group data into an object or an array is when you don’t know how many pieces of state you’ll need. For example, it’s helpful when you have a form where the user can add custom fields.

2021329 — Brightfield Microscope is also known as the Compound Light Microscope. It is an optical microscope that uses light rays to produce a dark image ...

If the state is too nested to update easily, consider making it “flat”. Here is one way you can restructure this data. Instead of a tree-like structure where each place has an array of its child places, you can have each place hold an array of its child place IDs. Then store a mapping from each place ID to the corresponding place.

Since isSending and isSent should never be true at the same time, it is better to replace them with one status state variable that may take one of three valid states: 'typing' (initial), 'sending', and 'sent':

Can PromeAI's Creative Fusion be used for professional design work? Absolutely, this AI Fusion Generator is designed to cater to professionals in architecture, ...

Sometimes, you can also reduce state nesting by moving some of the nested state into the child components. This works well for ephemeral UI state that doesn’t need to be stored, like whether an item is hovered.

Although you could update selectedItem too, an easier fix is to remove duplication. In this example, instead of a selectedItem object (which creates a duplication with objects inside items), you hold the selectedId in state, and then get the selectedItem by searching the items array for an item with that ID:

This is why “mirroring” some prop in a state variable can lead to confusion. Instead, use the messageColor prop directly in your code. If you want to give it a shorter name, use a constant:

This form has three state variables: firstName, lastName, and fullName. However, fullName is redundant. You can always calculate fullName from firstName and lastName during render, so remove it from state.

When you write a component that holds some state, you’ll have to make choices about how many state variables to use and what the shape of their data should be. While it’s possible to write correct programs even with a suboptimal state structure, there are a few principles that can guide you to make better choices:

While this code works, it leaves the door open for “impossible” states. For example, if you forget to call setIsSent and setIsSending together, you may end up in a situation where both isSending and isSent are true at the same time. The more complex your component is, the harder it is to understand what happened.

Ideally, you would also remove the deleted items (and their children!) from the “table” object to improve memory usage. This version does that. It also uses Immer to make the update logic more concise.

Flashing lights when eyes closed headache

Now if you edit the selected item, the message below will update immediately. This is because setItems triggers a re-render, and items.find(...) would find the item with the updated title. You didn’t need to hold the selected item in state, because only the selected ID is essential. The rest could be calculated during render.

Now let’s say you want to add a button to delete a place you’ve already visited. How would you go about it? Updating nested state involves making copies of objects all the way up from the part that changed. Deleting a deeply nested place would involve copying its entire parent place chain. Such code can be very verbose.

Currently, it stores the selected item as an object in the selectedItem state variable. However, this is not great: the contents of the selectedItem is the same object as one of the items inside the items list. This means that the information about the item itself is duplicated in two places.

202464 — That's right—the same color, the same room, different walls. You should do this when sampling paint colors, as suggested in the above link.

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Notice how if you first click “Choose” on an item and then edit it, the input updates but the label at the bottom does not reflect the edits. This is because you have duplicated state, and you forgot to update selectedItem.

”Mirroring” props into state only makes sense when you want to ignore all updates for a specific prop. By convention, start the prop name with initial or default to clarify that its new values are ignored:

If you can calculate some information from the component’s props or its existing state variables during rendering, you should not put that information into that component’s state.