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2.2.43 • Public • Published


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This project is part of the @thi.ng/umbrella monorepo and anti-framework.


Declarative, functional & typechecked CLI argument/options parser, value coercions etc..

Includes built-in support for the following argument types (of course custom arg types are supported too):

Argument type Multiple Example Result
Flag --force, -f force: true
String --foo bar foo: "bar"
Float/int/hex --bg ff997f bg: 16750975
Enum --type png type: "png"
KV pairs --define foo=bar define: { foo: "bar" }
KV multi pairs -D foo=bar -D foo=baz define: { foo: ["bar", "baz"] }
JSON --config '{"foo": [23]}' config: { foo: [23] }
Fixed size tuple --size 640x480 size: { value: [640, 480] }

If multiple values/repetitions are allowed for an argument, the values will be collected into an array (apart from KV pairs, which will yield an object). Furthermore, for multi-args, an optional delimiter can be specified to extract individual values, e.g. -a 1,2,3 equals -a 1 -a 2 -a 3


STABLE - used in production

Search or submit any issues for this package


yarn add @thi.ng/args

ES module import:

<script type="module" src="https://cdn.skypack.dev/@thi.ng/args"></script>

Skypack documentation

For Node.js REPL:

const args = await import("@thi.ng/args");

Package sizes (brotli'd, pre-treeshake): ESM: 2.39 KB



Generated API docs

Basic usage

import {
    type Args,
    type KVDict,
    type Tuple,
} from "@thi.ng/args";

type ImgType = "png" | "jpg" | "gif" | "tiff";

// CLI args will be validated against this interface
interface TestArgs {
    configPath?: string;
    force?: boolean;
    bg: number;
    type: ImgType;
    size?: Tuple<number>;
    pos?: Tuple<number>;
    xtra?: { a: number; b: string };
    define?: KVDict;

// arg specifications
const specs: Args<TestArgs> = {
    // string arg
    configPath: string({
        alias: "c",
        hint: "PATH",
        desc: "Config file path (CLI args always take precedence over those settings)",
    // boolean flag (default: false)
    force: flag({
        alias: "f",
        desc: "Force operation",
        // side effect & predicate
        // parsing only continues if fn returns true
        fn: (_) => (console.log("force mode enabled"), true),
    // hex int value
    bg: hex({
        desc: "Background color",
        // mandatory args require a `default` value and/or `optional: false`
        default: 0xffffff,
        defaultHint: "ffffff",
    // enum value (mandatory)
    type: oneOf(["png", "jpg", "gif", "tiff"], {
        alias: "t",
        desc: "Image type",
        // mandatory args require a `default` value and/or `optional: false`
        optional: false,
    // fixed size numeric tuple w/ `x` as delimiter
    // size: tuple(coerceInt, 2, { hint: "WxH", desc: "Target size" }, "x"),
    // syntax sugar for above:
    size: size(2, { hint: "WxH", desc: "Target size" }),
    // another version for tuples of floating point values
    // pos: tuple(coerceFloat, 2, { desc: "Lat/Lon" }, ","),
    pos: vec(2, { desc: "Lat/Lon coordinates" }),
    // JSON string arg
    xtra: json({
        alias: "x",
        desc: "Extra options",
        group: "extra",
    // key-value pairs parsed into an object
    define: kvPairs({
        alias: "D",
        desc: "Define dict entry",
        group: "extra"

try {
    // parse argv w/ above argument specs & default options
    // (by default usage is shown if error occurs)
    const args = parse(specs, process.argv, {
        usageOpts: {
            prefix: `
 █ █   █           │
██ █               │
 █ █ █ █   █ █ █ █ │ @thi.ng/args demo app
 █ █ █ █ █ █ █ █ █ │ v1.0.0
                 █ │
               █ █ │\n\n`,
            showGroupNames: true,
            groups: ["flags", "main", "extra"],
            lineWidth: 72,
} catch (_) {}

Invoking this as CLI script without arguments will generate an error about a missing --type arg and output the generated usage info (by default with ANSI color highlights):

illegal argument(s): missing arg: --type

 █ █   █           │
██ █               │
 █ █ █ █   █ █ █ █ │ @thi.ng/args demo app
 █ █ █ █ █ █ █ █ █ │ v1.0.0
                 █ │
               █ █ │


-f, --force                     Force operation


--bg HEX                        Background color (default: "ffffff")
-c PATH, --config-path PATH     Config file path (CLI args always take
                                precedence over those settings)
--pos N,N                       Lat/Lon coordinates
--size WxH                      Target size
-t ID, --type ID                [required] Image type: "png", "jpg",
                                "gif", "tiff"


-D key=val, --define key=val    [multiple] Define dict entry
-x JSON, --xtra JSON            Extra options

Generate & display help

Usage information can be generated via usage() and is automatically triggered via the special --help option (configurable, see ParseOpts).

Each arg can be associated with arbitrary group IDs, which are then used to segment usage output. By default, flag() args are assigned to a "flags" group, all others to "main". The default output order too is ["flags", "main"], but can be configured via a group option given an arg spec or factory function.

By default, ANSI colors are used to format the result string of usage(), but can be disabled (see UsageOpts).

ts-node index.ts --help

-f, --force                     Force operation

--bg HEX                        Background color
-c PATH, --config-path PATH     Config file path (CLI args always take
                                precedence over those settings)
-D key=val, --define key=val    [multiple] Define dict entry
--pos N,N                       Lat/Lon
--size WxH                      Target size
-t ID, --type ID                [required] Image type: 'png', 'jpg', 'gif',
-x JSON, --xtra JSON            Extra options

Parsing, value coercions & side effects

The below invocation demonstrates how the various argument types are handled & represented in the result. Parsing stops with the first non-argument value (here sourcefile.png) and the remaining values are made available via rest in the result object.

ts-node index.ts \
    -f -t png --bg ff00ff --size 640x480 \
    -D author=toxi -D date=2018-03-24 \
    --xtra '{"foo": [23]}' \

# force mode enabled
# {
#   result: {
#     force: true,
#     type: 'png',
#     bg: 16711935,
#     size: Tuple { value: [640, 480] }
#     define: { author: 'toxi', date: '2018-03-24' },
#     xtra: { foo: [23] },
#   },
#   index: 15,
#   rest: [ 'sourcefile.png' ],
#   done: false
# }


If this project contributes to an academic publication, please cite it as:

  title = "@thi.ng/args",
  author = "Karsten Schmidt",
  note = "https://thi.ng/args",
  year = 2018


© 2018 - 2023 Karsten Schmidt // Apache License 2.0

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