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Uses new Rust 2021

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#138 in WebAssembly

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Used in 9 crates (8 directly)

MIT license


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deno doc Build Status - Cirrus Twitter handle Discord Chat

The module graph/dependency logic for the Deno CLI.

This repository is a Rust crate which provides the foundational code to be able to build a module graph, following the Deno CLI's module resolution logic. It also provides a web assembly interface to the built code, making it possible to leverage the logic outside of the Deno CLI from JavaScript/TypeScript.

Rust usage


create_graph() is the main way of interfacing with the crate. It requires the root module specifiers/URLs for the graph and an implementation of the source::Loader trait. It also optionally takes implementations of the source::Resolver and source::Locker traits. It will load and parse the root module and recursively all of its dependencies, returning asynchronously a resulting ModuleGraph.

source::Loader trait

Implementing this trait requires the load() method and optionally the get_cache_into() method. The load() method returns a future with the requested module specifier and the resulting load response. This allows the module graph to deal with redirections, error conditions, and local and remote content.

The get_cache_info() is the API for exposing additional meta data about a module specifier as it resides in the cache so it can be part of a module graphs information. When the graph is built, the method will be called with each resolved module in the graph to see if the additional information is available.

source::Resolver trait

This trait "replaces" the default resolution logic of the module graph. It is intended to allow concepts like import maps and alternative resolution logic to "plug" into the module graph.

It has two methods, resolve and resolve_types, which both have default implementations. resolve takes the string specifier from the source and the referring specifier and is expected to return a result with the resolved specifier.

resolve_types takes a specifier and is expected to return a result with an optional module specifier and optional source range of the types that should be used. For example, if you are trying represent the "typings" field from a package.json file, when you receive the request on resolve_types for the main module of the package, you would respond with the absolute specifier to the types along with a range that indicates the file URL to the package.json and the range where it was specified. Including the range is useful to allow errors produced from the graph to indicate "where" the dependency came from.

source::Locker trait

This trait allows the module graph to perform sub-resource integrity checks on a module graph.

source::MemoryLoader struct

MemoryLoader is a structure that implements the source::Loader trait and is designed so that a cache of modules can be stored in memory to be parsed and retrieved when building a module graph. This is useful for testing purposes or in situations where the module contents is already available and dynamically loading them is not practical or desirable.

A minimal example would look like this:

use deno_graph::create_graph;
use deno_graph::ModuleSpecifier;
use deno_graph::source::MemoryLoader;
use futures::executor::block_on;

fn main() {
  let mut loader = MemoryLoader::new(
      ("file:///test.ts", Ok(("file:///test.ts", None, "import * as a from \"./a.ts\";"))),
      ("file:///a.ts", Ok(("file:///a.ts", None, "export const a = \"a\";"))),
  let roots = vec![ModuleSpecifier::parse("file:///test.ts").unwrap()];
  let future = async move {
    let graph = create_graph(roots, &mut loader, None, None).await;
    println!("{}", graph);

Other core concepts

ModuleSpecifier type alias

Currently part of the the deno_core crate. deno_graph explicitly doesn't depend on deno_core or any part of the Deno CLI. It exports the type alias publicably for re-use by other crates.

MediaType enum

Currently part of the deno_cli crate, this enum represents the various media types that the Deno CLI can resolve and handle. Since deno_graph doesn't rely upon any part of the Deno CLI, it was necessary to implement this in this crate, and the implementation here will eventually replace the implementation in deno_cli.

Usage from Deno CLI or Deploy

This repository includes a compiled version of the Rust crate as Web Assembly and exposes an interface which is availble via the mod.ts in this repository and can be imported like:

import * as denoGraph from "https://deno.land/x/deno_graph@{VERSION}/mod.ts";

Where {VERSION} should be substituted with the specific version you want to use.


The createGraph() function allows a module graph to be built asynchronously. It requires a root specifier or any array of root specifiers to be passed, which will serve as the roots of the module graph.

There are several options that can be passed the function in the optional options argument:

  • load - a callback function that takes a URL string and a flag indicating if the dependency was required dynamically (e.g. const m = await import("mod.ts")) and resolves with a LoadResponse. By default a load() function that will attempt to load local modules via Deno.readFile() and load remote modules via fetch().
  • cacheInfo - a callback function that takes a URL string and returns a CacheInfo object. In the Deno CLI, the DENO_DIR cache info is passed back using this interface. If the function is not provided, the information is not present in the module graph.
  • resolve - a callback function that takes a string and a referring URL string and returns a fully qualified URL string. In the Deno CLI, import maps provide this callback functionality of potentially resolving modules differently than the default resolution.
  • resolveTypes - a callback function that takes a URL string and returns the types dependency for the specifier, along with optionally the source of the types dependency. This only gets called in situations where the module is potentially untyped (e.g. JavaScript, JSX) and no other type dependency was detected. This is intended to enrich the module graph with external types that are resolved in some other fashion, like from a package.json or via detecting an @types typings package is available.
  • check - a callback function that takes a URL string and an Uint8Array of the byte content of a module to validate if that module sub resource integrity is valid. The callback should return true if it is, otherwise false. If the callback is not provided, all checks will pass.
  • getChecksum - a callback function that takes an Uint8Array of the byte content of a module in order to be able to return a string which represent a checksum of the provided data. If the callback is not provided, the checksum will be generated in line with the way the Deno CLI generates the checksum.

Replicating the Deno CLI

deno_graph is essentially a refactor of the module graph and related code as a stand alone crate which also targets Web Assembly and provides a JavaScript/TypeScript interface. This permits users of the package to be able to replicate the deno info command in Deno CLI within the runtime environment without requiring a Deno namespace API.

The module graph has two methods which provide the output of deno info. The method toString() provides the text output from deno info and toJSON() provides the JSON object structure from deno info --json.

ℹ️ currently, there is no runtime access to the DENO_DIR/Deno cache, and there is no default implementation of the API when creating a module graph, therefore cache information is missing from the output. An implementation of something that read the DENO_DIR cache is possible from CLI, but not currently implemented.

To replicate deno info https://deno.land/x/std/testing/asserts.ts, you would want to do something like this:

import { createGraph } from "https://deno.land/x/deno_graph@{VERSION}/mod.ts";

const graph = await createGraph("https://deno.land/x/std/testing/asserts.ts");


This would output to stdout and would respect the NO_COLOR/Deno.noColor setting. If colors are allowed, the string will include the ANSI color escape sequences, otherwise they will be omitted. This behavior can be explicitly overridden by passing true to always remove ANSI colors or false to force them.

To replicate deno info --json https://deno.land/x/std/testing/asserts.ts, you would want to do something like this:

import { createGraph } from "https://deno.land/x/deno_graph@{VERSION}/mod.ts";

const graph = await createGraph("https://deno.land/x/std/testing/asserts.ts");

console.log(JSON.stringify(graph, undefined, "  "));

This would output to stdout the JSON structure of the module graph.

Building Web Assembly

The build script (_build.ts) requires the Deno CLI to be installed and available in the path. If it is, the following command should just work:

> deno task build


We appreciate your help!

To contribute, please read our contributing instructions.

This repository includes .devcontainer metadata which will allow a development container to be built which has all the development pre-requisites available to make contribution easier.


~556K SLoC