I know that in React JSX style attribute must be an object. But I'm wondering why it can't be a plain string like normal HTML.
JSX is compiled to normal HTML by React.createElement under the hood.
React.createElement("div", {style:"color: red;"}, "Why does this throw an error?")
Why doesn't style get added to the element like any other normal HTML attribute?
It could, but it would require some extra code.
https://egghead.io/lessons/css-style-html-with-javascript-template-strings-and-objects-in-css-in-js
I guess the first question is, if it's really worth it.
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 would like to know how is it possible to create a custom rule, where I can define fobidden html elements in jsx syntax.
For example, I want to be sure that only <Button /> and <Input /> compontents from my ui library are used. If <input> or <button> html elements are used in jsx, eslint should throw an error.
If you want to create an ESLint rule by yourself (e.g. to learn something new) then this won't be helpful and it's certainly out of scope for a StackOverflow question, but if you need it for practical reasons, there is already a rule that does exactly what you want.
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.
I am currently learning React and Redux. I have forked a boilerplate, and currently I am looking through all of the code to see how it fits together.
While scanning through some React Component files I found something very interesting! When setting className for many of the elements the syntax they use differs. The first time they use the following syntax:
<span className={classes['counter--green']}>
...
</span>
Then this syntax:
<button className='btn btn-default'>
...
</button>
And from there on out they use the following:
<h2 className={classes.counterContainer}>
...
</h2>
At the top of the file they import classes with the following:
import classes from './Counter.scss'
So simply my question is, why are there three different syntax for className, and which one is correct?
Starting with the simple case:
<button className='btn btn-default'>
This just sets the class name to "btn btn-default". You need to set className instead of class since you are writing JSX and that’s equivalent to setting the className DOM property, so you have to use className here.
<span className={classes['counter--green']}>
<h2 className={classes.counterContainer}>
These are both very similar. In JSX, to specify a more complex JavaScript expression, you need to put it inside curly braces. This would be equivalent to setting the className property like this:
someSpan.className = classes['counter--green'];
someH2.className = classes.counterContainer;
Finally, classes as imported using the import classes from './Counter.scss' syntax is a feature called “CSS modules”. It involves a precompiler step that properly sets the class names later and makes sure that the style definitions are rendered to the HTML.
So to answer your final question, all of these are correct. What you want to use depends on where you want to define your styles (or where they are defined). Using CSS modules makes a lot of sense if you are creating independent components that might even get reused elsewhere. Using global CSS is good when you have an existing style sheet which you just want to use (e.g. here, these class names are likely from bootstrap). And of course, you can also mix these, if you have global styles and want to add additional styles to it.
In this case, without seeing the code, i'm guessing the boilerplate is using modular css (scss).
modular css can be imported,in this case as classes. Using modular css gives you css with local scope
all css rules imported from a module as classes are prefixed with the name classes.
and are to be treated as you treat object attributes
so css rule counterContainer is used as
classes.counterContainer
css rule name counter-green cannot use dot notation(because of the hyphen), so must use square bracket and string name notation as for any javascript object attribute
classes['counter-green']
the third example btn btn-default is not imported from a css classes module but is instead imported globally. This is possibly a bootstrap class imported at root level as a link attribute on the index.html
This isn't really unique to className, but for any JSX you can use curly braces {}'s to switch from "JSX mode" back to javascript to use any JS expression. Therefore in the first example they are setting the attribute className by referencing an object called classes by the property counter--green, in the second example they are using a simple JSX string literal 'btn btn-default', and in the third example they are referencing the classes object by the property counterContainer. You can see the definition of the classes object according to the import at the end of your question.
They are all correct, they are simply different ways of doing it. By using JS expressions they are arguably more modular, by using a string literal it is easier to see in front of you what is going on, but less re-usable.
I like a directive that conditionally puts a tag outside some content (but always prints the content), like this:
<p><strong ng-if-always-keep-inner-content="model.condition">{{model.text}}</strong>/p>
so if condition is true I get
<p><strong>yada yada</strong></p>
otherwise I get
<p>yada yada</p>
I could write it myself, but I want to know if it is possible to do with built in directives/options.
I should perhaps say this is used together with Bootstrap, which afaiu recommends using <strong> vs some class with a bold font.
I don't think there is a built in directive. You should write it.
I suggest to use a classic ng-if
<p ng-if="model.condition"><strong>{{model.text}}</strong></p>
<p ng-if="!model.condition">{{model.text}}</p>
In your specific case, you can also use ng-class and set the strong style via css.