I'm reading the react JS documentation and came across this:
Specifying Attributes with JSX:
You may use quotes to specify string literals as attributes:
const element = <div tabIndex="0"></div>;
I'm fairly comfortable with javascript but I'm not quite sure what the documentation means by "attributes". I know about object properties but this looks like a simple variable.
What exactly is a react js attribute if it is different from a property?
html elements have both attributes and properties
there are a few different scenarios for how they relate to each other. There doesn't necessarily have to be both an attribute or property for each value set on an element.
1. attributes
attributes can be set in html
<a id="mylink" href=""/>
where href is an attribute
or attributes can be set by using the set attribute method of an element
document.getElementById("mylink").setAttribute("href", "")
and read using
document.getElementById("mylink").getAttribute("href")
2. properties
properties can be set and read by retrieving the element as well
document.getElementById("mylink").href = ""
where href is a property
when they are set the first way, you are setting the attribute, the second sets the property.
Usually the underlying element attribute and property are
automatically synchronized, sometimes they are not.
Sometimes there is no matching attribute or property,
only one or the other exists.
Attributes and properties are part of native html elements, which React provides additional support and abstractions around.
Custom React components (such as <MyComponent prop=""/> or <MyComponent prop={someVar}/>), which you create yourself, accept props using the same syntax. The word props in this context refers purely to React props. React custom component props are just plain javascript values passed into your component. These custom components don't get added to the page. They are used to organize and render actual html elements.
When mounting a native component inside of a custom component (such as <div id=""/> or <div id={someVar}/>), the React library sets the underlying html attribute on the native browser element.
So there are two things to keep in mind here
html element attributes verse html element properties.
custom element props are neither of those, but setting a prop on a JSX
native element such as a div, set's the generated element's
attribute.
Now that's been established, the documentation above is saying: if you want to set an attribute value to a string you can use that specific syntax. That syntax only works for setting attribute values to strings.
You can use either:
<div id="myid"/>
or
<div id={'myid'} />
to set a string attribute value. They're probably just pointing out the syntax differences.
if you do:
<div tabIndex="0"/>
the value of tabIndex is the string 0 not the number zero
verses this:
<div tabIndex={0} />
which will pass the number zero to the tabindex attribute of the underlying html element
To me if we pass any parameter in function component then what we diclare in html is properties.But if you use (className/style/etc...) directecly in html then it will be attributes.
Related
https://reactjs.org/blog/2017/09/08/dom-attributes-in-react-16.html
As per this documentation, we do not need to have a data- as a prefix for a custom HTML attribute in JSX to appear in the actual DOM element without warning.
But when I try and use<div size="hello">my div element</div> it appears as <div>my div element</div> in actual DOM.
When I try <div Size="hello">my div element</div> then it appears correctly but it gives a warning.
What is the right way of adding size as a custom property on the HTML attribute?
example codepen here
Since the "size" attribute is a valid attribute for other tags but does not exist on the <div> element React strips it. In the documentation you referenced, it does state that you can prefix attributes with data-. "Just like before, React lets you pass data- and aria- attributes freely".
For obvious reasons, this is not recommended and should probably only be done if non-react scripts utilize the attribute.
To answer the question, if you have to store data in attributes, the best option is to prefix it with data-.
I can do any of:
React.RefObject<HTMLDivElement>
React.RefObject<HTMLInputElement>
React.RefObject<HTMLSpanElement>
But it doesn't work to do:
React.RefObject<HTMLAElement>
For <a> tags.
It seems they choose not to do a logical naming convention?
Cannot find any documentation which lists the conversion between 'HTML tag' and 'how react arbitrarily decided to call it'.
You can easily get the type of a element as follows (type in your browser console, not in a script):
const t = document.createElement('a');
console.log(t.__proto__);
As you can see a <a> element will be a HTMLAnchorElement. This is built into HTML and is not react/typescript specific. Replace 'a' with any other element to get it's type.
The a in the <a></a> element is stand for Anchor. So if you want to use the anchor element type you can simply use the HTMLAnchorElement.
According to the MDN documentation:
The HTMLAnchorElement interface represents hyperlink elements and provides special properties and methods (beyond those of the regular HTMLElement object interface that they inherit from) for manipulating the layout and presentation of such elements. This interface corresponds to element
You can also see the list of HTML types on the MDN web API's page, in H column.
I know that we can use css classes for the className attribute but I see in a lot of tutorials that even if the value written for className is not used in the css file it is still used in the components. Can someone explain why? Or how to determine the value of the className we need to use?
The HTML class attribute (as set by the React className attribute) is a general way to label elements with some meaningful labels. It can be used for CSS styling, or JavaScript queries like document.querySelectorAll, or just to make the HTML intent more readable.
In particular, it's common to include classes in your HTML in case you'll need them later for CSS styling or JavaScript queries. To be clear, there's no list of valid class names; you can use whatever names you want, and use or not use them in order code as you wish.
Working on a pre existing React JS project and the className attribute does not render in the DOM what is defined.
For example - here is what code looks like in the project:
<div className={styles.intro_inner}></div>
Here is the output in the DOM:
I'm expecting the class name "intro_inner" to appear within the DOM.
Within JSX, the syntax attribute={variable} on a component means that the attribute will be set with the value of the given variable, not it's name. I would assume that your code has an object named styles which has an attribute named intro_inner whose value is some random mash of characters that you see output in the inspector.
If you want the class to be set as "intro_inner" then you need to set it as a string, not a variable. The syntax for that would be className="intro_inner".
I read that in Angular, you can apply ngReadOnly or ngDisabled directive to a form field and it will convert it to a read only element.
I want to do something similar in React. Except, if I apply a directive or class or attribute like rctReadOnly on a container element such as <div>, <form>, <fieldset>, I want to recursively go through all child elements and:
convert form fields to read only equivalent
remove all html elements that have the class .action-^, for example .action-add, .action-delete, .action-bulk-update etc...
How do I achieve this in React?