import.meta.resolve()

import.meta.resolve() is a built-in function defined on the import.meta object of a JavaScript module that resolves a module specifier to a URL using the current module's URL as base.

Syntax

import.meta.resolve(moduleName)

Parameters

moduleName
- : A string that specifies a potentially importable module. This may be a relative path (such as "./lib/helper.js"), a bare name (such as "my-module"), or an absolute URL (such as "https://example.com/lib/helper.js").

Return value

Returns a string corresponding to the path that would be imported if the argument were passed to import().

Description

import.meta.resolve() allows a script to access the module specifier resolution algorithm for a name, like this:

// Script at https://example.com/main.js

const helperPath = import.meta.resolve("./lib/helper.js");
console.log(helperPath); // "https://example.com/lib/helper.js"

Note that import.meta.resolve() only performs resolution and does not attempt to load or import the resulting path. (The explainer for the specification describes the reasoning for this behavior.) Therefore, its return value is the same regardless of whether the returned path corresponds to a file that exists, and regardless of whether that file contains valid code for a module.

It is different from dynamic import, because although both accept a module specifier as the first argument, import.meta.resolve() returns the path that would be imported without making any attempt to access that path. Therefore, the following two are effectively the same code:

// Approach 1
console.log(await import("./lib/helper.js"));

// Approach 2
const helperPath = import.meta.resolve("./lib/helper.js");
console.log(await import(helperPath));

However, even if "./lib/helper.js" cannot be successfully imported, the second snippet will not encounter an error until it attempts to perform the import on line 2.

Bare module names

You can pass a bare module name (also known as a bare module specifier) to import.meta.resolve(), as long as module resolution is defined for the name. For example, you can define this using an import map inside a browser:

<!-- index.html -->
<script type="importmap">
  {
    "imports": {
      "my-module": "./modules/my-module/index.js"
    }
  }
</script>

<script type="module">
  const moduleEntryPath = import.meta.resolve("my-module");
  console.log(moduleEntryPath);
</script>

Again, since this snippet does not try to import moduleEntryPath — neither does the import map — it prints the resolved URL regardless of whether ./modules/my-module/index.js actually exists.

Comparison with new URL()

The URL() constructor accepts a second base URL argument. When the first argument is a relative path and the base URL is import.meta.url, the effect is similar to import.meta.resolve().

const helperPath = new URL("./lib/helper.js", import.meta.url).href;
console.log(helperPath);

This is also a useful replacement syntax when targeting older browsers. However, there are some differences:

import.meta.resolve() returns a string, while new URL() returns a URL object. It is possible to use href or toString() on the constructed URL, but this may still not produce the exact same result in some JavaScript environments or when using tools like bundlers to statically analyze the code.
import.meta.resolve() is aware of additional resolution configurations, such as resolving bare module names using import maps, as described above. new URL() is not aware of import maps and treats bare module names as relative paths (i.e. new URL("my-module", import.meta.url) means new URL("./my-module", import.meta.url)).

Some tools recognize new URL("./lib/helper.js", import.meta.url).href as a dependency on "./lib/helper.js" (similar to an import), and take this into account for features like bundling, rewriting imports for moved files, "go to source" functionality, etc. However, since import.meta.resolve() is less ambiguous and specifically designed to indicate a module path resolution dependency, you should use import.meta.resolve(moduleName) instead of new URL(moduleName, import.meta.url) for these use cases wherever possible.

Not an ECMAScript feature

import.meta.resolve() is not specified or documented as part of the ECMAScript specification for JavaScript modules. Instead, the specification defines the import.meta object but leaves all its properties as "host-defined". The WHATWG HTML standard picks up where the ECMAScript standard leaves off, and defines import.meta.resolve using its module specifier resolution.

This means that import.meta.resolve() is not required to be implemented by all conformant JavaScript implementations. However, import.meta.resolve() may also be available in non-browser environments:

Deno implements compatibility with browser behavior.
Node.js has an implementation that is available using the --experimental-import-meta-resolve and currently returns a Promise instead of a string, although this may change to match browsers.

Examples

Resolve a path for the Worker() constructor

import.meta.resolve() is particularly valuable for APIs that take a path to a script file as an argument, such as the Worker() constructor:

// main.js
const workerPath = import.meta.resolve("./worker.js");
const worker = new Worker(workerPath, { type: "module" });
worker.addEventListener("message", console.log);

// worker.js
self.postMessage("hello!");

This is also useful to calculate paths for other workers, such as service workers and shared workers. However, if you are using a relative path to calculate the URL of a service worker, keep in mind that the directory of the resolved path determines its registration scope by default (although a different scope can be specified during registration).