jsdelivr esm support

README.md

@@ -131,6 +131,33 @@ results in generating:
     {"imports":{"htmx":"https://unpkg.com/browse/htmx.org@1.8.6/dist/htmx.min.js"}}
 ```
 
+### jsdelivr ESM imports can be fetched using the jsdelivr provider:
+
+```go
+  im := importmap.
+    NewDefaults().
+    WithProvider(cdnjs.New()).
+    AssetsDir(path.Join("assets")).
+    WithPackages([]library.Package{
+    {
+      Name:    "htmx",
+      Version: "2.0.4",
+      Require: []library.Include{
+        {File: "htmx.esm.min.js"},
+        {File: "/ext/json-enc.js", As: "json-enc"},
+	  },
+	},{
+      Provider: jsdelivr.NewESM(), // <!-- Use jsdelivr ESM provider -->
+      Name:     "@simonwep/pickr",
+      Version:  "1.9.1",
+      Require: []library.Include{
+        {File: "/esm-bundle.js", As: "pickr"}, // <!-- Get the ESM bundle -->
+        {File: "/dist/themes/nano.min.css", As: "nano.min.css"},
+	  },
+	},
+  })
+```
+
 ## Contributing
 
 Contributions are welcome!

client/jsdelivr/jsdelivr.go

@@ -19,6 +19,7 @@ type (
 	Client struct {
 		apiBaseURL string
 		cdnBaseURL string
+		esm        bool
 	}
 
 	SearchResponse struct {
@@ -58,9 +59,26 @@ func New() *Client {
 	return &Client{
 		apiBaseURL: defaultApiBaseURL,
 		cdnBaseURL: defaultCdnBaseURL,
+		esm:        false,
 	}
 }
 
+// NewESM returns a new Client with ESM mode enabled
+func NewESM() *Client {
+	return &Client{
+		apiBaseURL: defaultApiBaseURL,
+		cdnBaseURL: defaultCdnBaseURL,
+		esm:        true,
+	}
+}
+
+// SetESM sets whether the client should use ESM mode
+func (c *Client) SetESM(useESM bool) *Client {
+	c.esm = useESM
+	return c
+}
+
+// FetchPackageFiles retrieves package files from jsdelivr
 func (c *Client) FetchPackageFiles(ctx context.Context, name, version string) (library.Files, string, error) {
 	url := defaultApiBaseURL + name
 
@@ -98,7 +116,7 @@ func (c *Client) FetchPackageFiles(ctx context.Context, name, version string) (l
 		}
 	}
 
-	// get all the files
+	// get all the files regardless of ESM mode - we need them for CSS and other file types
 	vUrl := fmt.Sprintf("%s%s@%s", defaultApiBaseURL, name, useVersion)
 
 	req, err = http.NewRequestWithContext(ctx, http.MethodGet, vUrl, nil)
@@ -131,6 +149,30 @@ func (c *Client) FetchPackageFiles(ctx context.Context, name, version string) (l
 
 	var files = walkFiles(pr.Files, basePath, "", hasDist)
 
+	// If ESM mode is enabled, we'll replace JS files with the ESM version
+	if c.esm {
+		// Create special ESM file with a unique LocalPath that will match any pattern
+		esmBasePath := c.cdnBaseURL + name + "@" + useVersion + "/+esm"
+
+		// Use a simpler approach - just add the ESM bundle with a standard path
+		esmFile := library.File{
+			Type:      library.FileTypeJS,
+			Path:      esmBasePath,
+			LocalPath: "/esm-bundle.js", // Simple filename without special characters
+		}
+
+		// Filter out JavaScript files, keeping only CSS and other files
+		var nonJSFiles library.Files
+		for _, file := range files {
+			if file.Type != library.FileTypeJS {
+				nonJSFiles = append(nonJSFiles, file)
+			}
+		}
+
+		// Combine the ESM file with non-JS files
+		files = append(library.Files{esmFile}, nonJSFiles...)
+	}
+
 	return files, useVersion, nil
 }