JSX spread children

[thejimmylin]

Basically I want to write something like this:

The problems

const App = () => {
    return <div>{...["Hello", " ", "spread", " ", "children"]}</div>
}

And I wish esbuild could turn it to something like:

const App = () => {
    return h("div", null, ...["Hello", " ", "spread", " ", "children"]);
};

But that is not the case, esbuild will turn it to something else. I will show it below.

And also, I find it possible when I use TS to translate JSX like this example in TS playground.

More information

Here are some output for esbuild/tsc and tsx/jsx.

Input

The intput is always these code, but with .tsx and .jsx extension.

import * as React from "react";
function Greet() {
  return <h1>{["Hello", " ", "world!"]}</h1>;
}
function SpreadGreet() {
  return <h1>{...["Hello", " ", "world!"]}</h1>;
}

Output1 - .tsx + esbuild

esbuild index.tsx --outfile=esbuild-tsx-output/index.js

import * as React from "react";
function Greet() {
  return /* @__PURE__ */ React.createElement("h1", null, ["Hello", " ", "world!"]);
}
function SpreadGreet() {
  return /* @__PURE__ */ React.createElement("h1", null, ["Hello", " ", "world!"]);
}

Output2 - .tsx + tsc

tsc index.tsx --target es6 --moduleResolution node --jsx react --outdir tsc-tsx-output/

import * as React from "react";
function Greet() {
    return React.createElement("h1", null, ["Hello", " ", "world!"]);
}
function SpreadGreet() {
    return React.createElement("h1", null, ...["Hello", " ", "world!"]);
}

Output3 - .jsx + esbuild

esbuild index.jsx --outfile=esbuild-jsx-output/index.js

✘ [ERROR] Unexpected "..."

    index.jsx:6:14:
      6 │   return <h1>{...["Hello", " ", "world!"]}</h1>;
        ╵               ~~~

1 error

Output4 - .jsx + tsc

tsc index.jsx --allowjs --target es6 --moduleResolution node --jsx react --outdir tsc-jsx-output/

import * as React from "react";
function Greet() {
    return React.createElement("h1", null, ["Hello", " ", "world!"]);
}
function SpreadGreet() {
    return React.createElement("h1", null, ...["Hello", " ", "world!"]);
}

You may reproduce the results above about with this repo.

Why this is a problem

As this issue has mentioned, JSX spread children is a nice feature and is technically possible.

React itself don't want/need this because it want its users to use the key prop to structure an array of JSX node and React will flatten these nested array later, when it structure the JSX tree/VDOM things.

However, that is actually more like an implementation detail, which should not be noticed by those who use JSX without React. It will be great if esbuild allows these syntax.

[evanw]

Makes sense. Looks like TypeScript's behavior regarding this changed in TypeScript 4.5+, and esbuild should be updated to match this new behavior from the TypeScript compiler.

[thejimmylin]

Thanks a lot! :))

Edit:
A just noticed that the new esbuild@0.14.39 is updated to match this behavior. That is fast! Thank you!!