[lhorie]

DOM.div() vs <div/> seems like a bad example. IMHO, when you get an element with tons of event handlers and conditional classes, or when you have a deep chain of ternaries that's where angled bracket syntax starts to become unwieldy.

The className thing is a big deal too, in my opinion. Preact and Mithril do what you would expect, and perf doesn't suffer, so why can't React/JSX normalize it as well?

[debaserab2]

If you have deep chains of ternarys, that's a symptom that you should be splitting your rendering code into another function or component. This would be true regardless or what approach you are taking to templatihg.

That's one thing I really appreciate about jsx: the lack of rich template code syntax makes it glaringly obvious when your template code is doing too much and should be refactored. It does a really good job of keeping your logic in javascript and out of your template.

[lhorie]

Refactoring into functions/components doesn't magically make a complex ternary tree go away. It helps the body of each branch be less noisy but the ternary tree will still be there.

You're talking about taking something like `foo && bar || baz && quux` and turning it into `isSomeCondition()`, but that's a pretty obvious refactor in any templating system.

I'm talking about things like

    return (
      <div>{
        x.type === 'foo' ? <Something/> :
        x.type === 'bar' ? (
          <div>
            <h2>More stuff</h2>
            <Another data={x.data}/>
          </div>
        ) :
        x.type === 'baz' ? <Another data="baz"/> : null
      }</div>
    )

At this point, I think it's perfectly valid to have the opinion that JSX isn't helping much, since the JS-to-HTML ratio in this case is relatively high.

Refactoring would just make it more difficult to mentally piece things back together given you would end up with sparse component instantiations scattered amidst otherwise-procedural js code, as opposed to the more ideal single-root, declarative virtual dom tree.

[debaserab2]

Without understanding what x.type is, I'd be inclined to write that without any ternary operator at all using plain old if statements with each returning JSX markup. I try to keep logic in JSX to simple ternary operators and loops at most. JSX is really just shorthand for DOM.div() for me. I imagine the code structure looks pretty similar to actually using DOM.div though. I'm not seeing how programmatically creating markup with DOM.div results in significantly different code, although if you have some good examples I'd love to understand them better.

[lhorie]

Those are two different aspects of template code.

Pulling things out into plain if statements is fine if you only have one or two, but in my opinion, it gets progressively harder to understand the code as the number of if statements increase (for the same reason that writing vanilla DOM creation code does). In my experience, when this type of refactor is allowed, it's common to pull just about everything up to the top of the render function (conditional className compositions, conditional components, even loops). This increases cognitive load because now the maintainer has to mentally piece everything back together on every read. Having been that maintainer, I'd say it's the sort of code that it's fun to write, but not fun to read.

The rationales in favor of hyperscript are largely cosmetic (e.g. JS indents more naturally), and I think that's very much a potato-potahto kind of discussion. Personally, I feel that hyperscript is more readable (because of the terser CSS selector syntax), but likewise, I totally understand that some people find angled brackets easier to read even if that entails super long attribute lists.

[acemarke]

Yep. I very much prefer to keep all the actual _logic_ outside the JSX structure, and storing all conditional stuff in temp variables. I have an example of my preferred approach at https://gist.github.com/markerikson/47fff93c92286db72b22bab5... .

[debaserab2]

That's exactly how I do it, too!

[nkohari]

Ternary operators should never be nested, whether you're using JSX or not. If you have that many conditionals you should use variables and/or decompose the optional pieces into sub-components. Pretty much any time you have a tag that has a huge number of attributes, it's a smell that you need to decompose something.

Variable assignment is the simplest answer, which takes advantage of the fact that null or undefined values are ignored in JSX:

    const Dashboard = (props) => {
      let avatar;
      if (props.user) avatar = <Avatar user={props.user} />;
      return (
        <div>
          {avatar}
          ...some other content...
        </div>
      );
    };

Regarding class vs. className: class is a reserved word in JS. It's not really a perf thing, it's the fact that JSX was intended as a very simple transform. If JSX used class instead of className, the transpiler would need to be contextual since "class" would sometimes mean "css class" and sometimes "JavaScript class". The baseline complexity for the parser would be higher and could lead to all sorts of complexity. Rather than deal with that the React team avoided the problem by using className instead, keeping things simple.

[duncanawoods]

I think this proves lhorie's point. Markup syntax is dominated by code when you are building complex dynamic apps instead of static documents. What do you really gain by putting angle brackets around Avatar instead of calling a function?

FWIW I believe new react devs are slow to realise they can use local variables like this because JSX looks like it is doing string templating instead of object instantiation.

[nkohari]

The example I gave was simplistic, but the value of JSX is the ability to easily nest elements. For instance, let's take my previous example and say we're creating a profile link:

    const Dashboard = (props) => {
      const {user} = props;
      let link;
      if (user) {
        link = (
          <a href="...">
            <Avatar user={user} />
            <span>{user.name}</span>
          </a>
        );
      }
      return (
        <div>
          {link}
          ...some other content...
        </div>
      );
    };

If you want, you could create a `createProfileLink()` function, or you could create a `ProfileLink` component, or you could keep it as a variable in the `render()` function. This flexibility is what makes JSX powerful.

[duncanawoods]

> but the value of JSX is the ability to easily nest elements

There is nothing there that "makes JSX so powerful", its just hiding function calls and varargs. Its only xml-ish syntax. You are welcome to prefer it but its not adding anything functional beyond that.

    const Dashboard = (props) => {
      const {user} = props;
      let link;
      if (user) {
        link = 
            DOM.a({href: "..."},
                Components.Avatar(user),
                DOM.span(user.name));
      }
      return 
        DOM.div(link, ...some other content);
    };

[nkohari]

Yes, I understand how JSX works. My point is that it permits nesting in a syntax that is much simpler and emulates markup, which is familiar to web developers.

It's okay if you prefer to write code using the direct function calls, but I'm not sure most people would agree with you. I've built a product using direct calls (in CoffeeScript) and using JSX, and JSX was far easier to work with and less error-prone. YMMV.

[lhorie]

I disagree in two ways: the first is that the ability to write template composition procedurally isn't specific to JSX. You can do that in plain js/hyperscript just as well.

The second point is precisely that this is procedural code. If the ability of putting together templates procedurally is the pinnacle of templating power/expressiveness, we might as well go back to Backbone.js.

[zeven7]

    > Regarding class vs. className: class is a reserved word
    > in JS. It's not really a perf thing, it's the fact that
    > JSX was intended as a very simple transform. If JSX used
    > class instead of className, the transpiler would need to
    > be contextual since "class" would sometimes mean "css
    > class" and sometimes "JavaScript class".

I don't think React should have used `class` instead of `className`, but this isn't the reason.

    <foo className="bar" />

compiles to

    React.createElement("foo", { className: "bar" });

It could have just as easily have been that

    <foo class="bar" />

compiles to

    React.createElement("foo", { 'class': "bar" });

as far as JSX is concerned (or even without the quotes in an ES5 world).

[nkohari]

The output isn't the problem; it's that "class" is also a keyword in the JSX input. I admit, though, I'm not intimately familiar with the JSX transpiler and am just guessing as to their motives.

[lhorie]

I'm actually fine w/ JSX being "dumb" and just translating `class` to `class`, but when used in conjunction w/ React, the end result is that the JSX "markup" has a lot of traps that simply don't exist in similar libraries like Mithril.

`className` isn't the only offender. `onClick` and `readOnly` are other notorious one. And then there's stuff like `xlinkHref`, because it's not like anyone ever imports SVG from external tools.

[Bahamut]

className was named that to avoid conflict with the JS class syntax originally I believe, since JSX is inline - they probably could put in the work to change it at this point, but it seems like a minimally beneficial change but massively disruptive at this point.

[jmtulloss]

It was named that to match the DOM api[0], which React does whenever possible. The DOM api is probably named for the reason you state.

[0]: https://developer.mozilla.org/en-US/docs/Web/API/Element/cla...

[rmetzler]

And the reason why the DOM API uses className is: class is a reserved keyword in JavaScript for a long time.

[lhorie]

There's also stuff like onClick, readOnly, xlinkHref... I would guess that a healthy number of React-related google searches are related to these gotchas