Civet

The Modern Way to Write TypeScript

Expressive Syntax and Faster Coding with Civet

Civet playground

Civet is a programming language that compiles to TypeScript or JavaScript, so you can use existing tooling but enable concise and powerful syntax. In addition to 99% JS/TS compatibility, there are many features, with some highlights below and more comprehensive examples on the cheatsheet. See also Civet's design philosophy.

Highlights: Beyond TC39

Civet code on the lefttop, compiled TypeScript output on the rightbottom.

Pattern Matching

TC39 Proposal: Pattern Matching

switch x
  0
    console.log("zero")
  /^\s+$/
    console.log("whitespace")
  [{type: "text", content}, ...rest]
    console.log("leading text", content)

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if (x === 0) {
  console.log("zero");
} else if (
  typeof x === "string" &&
  /^\s+$/.test(x)
) {
  console.log("whitespace");
} else if (
  Array.isArray(x) &&
  x.length >= 1 &&
  typeof x[0] === "object" &&
  x[0] != null &&
  "type" in x[0] &&
  x[0].type === "text" &&
  "content" in x[0]
) {
  const [{ type, content }, ...rest] = x;
  console.log("leading text", content);
}

Ligatures

Pipelines

TC39 Proposal: Pipe Operator

data
  |> Object.keys
  |> console.log

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console.log(Object.keys(data));

Ligatures

Pipe expression with shorthand functions:

a |> & + 1 |> bar

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bar(a + 1);

Ligatures

Single-Argument Function Shorthand

x.map .name
x.map &.profile?.name[0...3]
x.map &.callback a, b
x.map &+1
x.map -&

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x.map(($) => $.name);
x.map(($1) => $1.profile?.name.slice(0, 3));
x.map(($2) => $2.callback(a, b));
x.map(($3) => $3 + 1);
x.map(($4) => -$4);

Ligatures

Custom Infix Operators

operator {min, max} := Math
value min ceiling max floor

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const { min, max } = Math;
max(min(value, ceiling), floor);

Ligatures

Declarations in Conditions and Loops

if match := regex.exec string
  console.log match

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let ref;
if ((ref = regex.exec(string))) {
  const match = ref;
  console.log(match);
}

Ligatures

Everything is an Expression

items = for item of items
  if item.length
    item.toUpperCase()
  else
    "<empty>"

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items = (() => {
  const results = [];
  for (const item of items) {
    if (item.length) {
      results.push(item.toUpperCase());
    } else {
      results.push("<empty>");
    }
  }
  return results;
})();

Ligatures

return
  if x == null
    throw "x is null"
  else
    log `received x of ${x}`
    x.value()

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return x == null
  ? (() => {
      throw "x is null";
    })()
  : (log(`received x of ${x}`), x.value());

Ligatures

TC39 proposal: do expressions

x = do
  const tmp = f()
  tmp * tmp + 1

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x = (() => {
  {
    const tmp = f();
    return tmp * tmp + 1;
  }
})();

Ligatures

Dedented Strings and Templates

TC39 Proposal: String Dedent

text = """
  This text is a string that doesn't include
  the leading whitespace.
"""

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text = `This text is a string that doesn't include
the leading whitespace.`;

Ligatures

text = ```
  Also works for
  ${templates}!
```

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text = `Also works for
${templates}!`;

Ligatures

Chained Comparisons

a < b <= c
a is b is not c
a instanceof b not instanceof c

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a < b && b <= c;
a === b && b !== c;
a instanceof b && !(b instanceof c);

Ligatures

Default to `const` for Iteration Items

for (item of [1, 2, 3, 4, 5]) {
  console.log(item * item);
}

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for (const item of [1, 2, 3, 4, 5]) {
  console.log(item * item);
}

Ligatures

Spread in Any Position

Spreads in first or middle position:

[...head, last] = [1, 2, 3, 4, 5]

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const splice: <T>(
  this: T[],
  start: number,
  deleteCount?: number
) => T[] = [].splice as any;
([...head] = [1, 2, 3, 4, 5]),
  ([last] = splice.call(head, -1));

Ligatures

{a, ...rest, b} = {a: 7, b: 8, x: 0, y: 1}

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({ a, b, ...rest } = { a: 7, b: 8, x: 0, y: 1 });

Ligatures

function justDoIt(a, ...args, cb) {
  cb.apply(a, args)
}

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const splice: <T>(
  this: T[],
  start: number,
  deleteCount?: number
) => T[] = [].splice as any;
function justDoIt(a, ...args) {
  let [cb] = splice.call(args, -1);
  return cb.apply(a, args);
}

Ligatures

Import Syntax Matches Destructuring

import {X: LocalX, Y: LocalY} from "./util"

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import { X as LocalX, Y as LocalY } from "./util";

Ligatures

Export Convenience

export a, b, c from "./cool.js"
export x = 3

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export { a, b, c } from "./cool.js";
export var x = 3;

Ligatures

JSX

function Listing(props)
  <h1 #heading>Hello Civet!
  <ul .items>
    <For each=props.items>
      (item) =>
        <li .item {props.style}><Item {item}>

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function Listing(props) {
  return (
    <>
      <h1 id="heading">Hello Civet!</h1>
      <ul class="items">
        <For each={props.items}>
          {(item) => {
            return (
              <li
                class="item"
                style={props.style}
              >
                <Item item={item} />
              </li>
            );
          }}
        </For>
      </ul>
    </>
  );
}

Ligatures

Sponsors

Thank you to all of our sponsors for your invaluable support and contribution to the Civet language!

Support the future development of Civet!

Contributors

Thank you for your work and dedication to the Civet project!