diff --git a/src/format_text.rs b/src/format_text.rs
index da3e9e1..9b386d8 100644
--- a/src/format_text.rs
+++ b/src/format_text.rs
@@ -35,18 +35,18 @@ use super::swc::parse_swc_ast;
 /// // now format many files (it is recommended to parallelize this)
 /// let files_to_format = vec![(PathBuf::from("path/to/file.ts"), "const  t  =  5 ;")];
 /// for (file_path, file_text) in files_to_format {
-///     let result = format_text(&file_path, file_text.into(), &config);
+///     let result = format_text(&file_path, None, file_text.into(), &config);
 ///     // save result here...
 /// }
 /// ```
-pub fn format_text(file_path: &Path, file_text: String, config: &Configuration) -> Result<Option<String>> {
+pub fn format_text(file_path: &Path, file_extension: Option<&str>, file_text: String, config: &Configuration) -> Result<Option<String>> {
   if super::utils::file_text_has_ignore_comment(&file_text, &config.ignore_file_comment_text) {
     Ok(None)
   } else {
     let had_bom = file_text.starts_with("\u{FEFF}");
     let file_text = if had_bom { file_text[3..].to_string() } else { file_text };
     let file_text: Arc<str> = file_text.into();
-    let parsed_source = parse_swc_ast(file_path, file_text)?;
+    let parsed_source = parse_swc_ast(file_path, file_extension, file_text)?;
     match inner_format(&parsed_source, config)? {
       Some(new_text) => Ok(Some(new_text)),
       None => {
@@ -89,7 +89,7 @@ fn inner_format(parsed_source: &ParsedSource, config: &Configuration) -> Result<
 
 #[cfg(feature = "tracing")]
 pub fn trace_file(file_path: &Path, file_text: &str, config: &Configuration) -> dprint_core::formatting::TracingResult {
-  let parsed_source = parse_swc_ast(file_path, file_text.into()).unwrap();
+  let parsed_source = parse_swc_ast(file_path, None, file_text.into()).unwrap();
   ensure_no_specific_syntax_errors(&parsed_source).unwrap();
   dprint_core::formatting::trace_printing(|| generate(&parsed_source, config), config_to_print_options(file_text, config))
 }
@@ -111,7 +111,7 @@ mod test {
   fn strips_bom() {
     for input_text in ["\u{FEFF}const t = 5;\n", "\u{FEFF}const t =   5;"] {
       let config = crate::configuration::ConfigurationBuilder::new().build();
-      let result = format_text(&std::path::PathBuf::from("test.ts"), input_text.into(), &config).unwrap().unwrap();
+      let result = format_text(&std::path::PathBuf::from("test.ts"), None, input_text.into(), &config).unwrap().unwrap();
       assert_eq!(result, "const t = 5;\n");
     }
   }
diff --git a/src/swc.rs b/src/swc.rs
index f7a4728..0401f16 100644
--- a/src/swc.rs
+++ b/src/swc.rs
@@ -8,18 +8,18 @@ use deno_ast::ParsedSource;
 use std::path::Path;
 use std::sync::Arc;
 
-pub fn parse_swc_ast(file_path: &Path, file_text: Arc<str>) -> Result<ParsedSource> {
-  match parse_inner(file_path, file_text.clone()) {
+pub fn parse_swc_ast(file_path: &Path, file_extension: Option<&str>, file_text: Arc<str>) -> Result<ParsedSource> {
+  match parse_inner(file_path, file_extension, file_text.clone()) {
     Ok(result) => Ok(result),
     Err(err) => {
-      let lowercase_ext = get_lowercase_extension(file_path);
+      let lowercase_ext = file_extension.map(|ext| ext.to_string()).or_else(|| get_lowercase_extension(file_path));
       let new_file_path = match lowercase_ext.as_deref() {
         Some("ts") | Some("cts") | Some("mts") => file_path.with_extension("tsx"),
         Some("js") | Some("cjs") | Some("mjs") => file_path.with_extension("jsx"),
         _ => return Err(err),
       };
       // try to parse as jsx
-      match parse_inner(&new_file_path, file_text) {
+      match parse_inner(&new_file_path, None, file_text) {
         Ok(result) => Ok(result),
         Err(_) => Err(err), // return the original error
       }
@@ -27,14 +27,19 @@ pub fn parse_swc_ast(file_path: &Path, file_text: Arc<str>) -> Result<ParsedSour
   }
 }
 
-fn parse_inner(file_path: &Path, text: Arc<str>) -> Result<ParsedSource> {
-  let parsed_source = parse_inner_no_diagnostic_check(file_path, text)?;
+fn parse_inner(file_path: &Path, file_extension: Option<&str>, text: Arc<str>) -> Result<ParsedSource> {
+  let parsed_source = parse_inner_no_diagnostic_check(file_path, file_extension, text)?;
   ensure_no_specific_syntax_errors(&parsed_source)?;
   Ok(parsed_source)
 }
 
-fn parse_inner_no_diagnostic_check(file_path: &Path, text: Arc<str>) -> Result<ParsedSource> {
-  let media_type = deno_ast::MediaType::from_path(file_path);
+fn parse_inner_no_diagnostic_check(file_path: &Path, file_extension: Option<&str>, text: Arc<str>) -> Result<ParsedSource> {
+  let media_type = if let Some(file_extension) = file_extension {
+    deno_ast::MediaType::from_path(&file_path.with_extension(file_extension))
+  } else {
+    deno_ast::MediaType::from_path(file_path)
+  };
+
   let mut syntax = deno_ast::get_syntax(media_type);
   if let Syntax::Es(es) = &mut syntax {
     // support decorators in js
@@ -260,7 +265,7 @@ mod tests {
 
   fn run_fatal_diagnostic_test(file_path: &str, text: &str, expected: &str) {
     let file_path = PathBuf::from(file_path);
-    assert_eq!(parse_swc_ast(&file_path, text.into()).err().unwrap().to_string(), expected);
+    assert_eq!(parse_swc_ast(&file_path, None, text.into()).err().unwrap().to_string(), expected);
   }
 
   #[test]
@@ -286,6 +291,12 @@ mod tests {
     );
   }
 
+  #[test]
+  fn file_extension_overwrite() {
+    let file_path = PathBuf::from("./test.js");
+    assert!(parse_swc_ast(&file_path, Some("ts"), "const foo: string = 'bar';".into()).is_ok());
+  }
+
   #[test]
   fn it_should_error_for_exected_close_brace() {
     // swc can parse this, but we explicitly fail formatting
@@ -342,11 +353,11 @@ Merge conflict marker encountered. at file:///test.ts:6:1
 
   fn run_non_fatal_diagnostic_test(file_path: &str, text: &str, expected: &str) {
     let file_path = PathBuf::from(file_path);
-    assert_eq!(format!("{}", parse_swc_ast(&file_path, text.into()).err().unwrap()), expected);
+    assert_eq!(format!("{}", parse_swc_ast(&file_path, None, text.into()).err().unwrap()), expected);
 
     // this error should also be surfaced in `format_parsed_source` if someone provides
     // a source file that had a non-fatal diagnostic
-    let parsed_source = parse_inner_no_diagnostic_check(&file_path, text.into()).unwrap();
+    let parsed_source = parse_inner_no_diagnostic_check(&file_path, None, text.into()).unwrap();
     let config = ConfigurationBuilder::new().build();
     assert_eq!(crate::format_parsed_source(&parsed_source, &config).err().unwrap().to_string(), expected);
   }
diff --git a/src/wasm_plugin.rs b/src/wasm_plugin.rs
index a6a4296..69b7d14 100644
--- a/src/wasm_plugin.rs
+++ b/src/wasm_plugin.rs
@@ -58,7 +58,7 @@ impl SyncPluginHandler<Configuration> for TypeScriptPluginHandler {
     _format_with_host: impl FnMut(&Path, Vec<u8>, &ConfigKeyMap) -> FormatResult,
   ) -> FormatResult {
     let file_text = String::from_utf8(file_bytes)?;
-    super::format_text(file_path, file_text, config).map(|maybe_text| maybe_text.map(|t| t.into_bytes()))
+    super::format_text(file_path, None, file_text, config).map(|maybe_text| maybe_text.map(|t| t.into_bytes()))
   }
 }
 
diff --git a/tests/spec_test.rs b/tests/spec_test.rs
index a4a510c..c0c429c 100644
--- a/tests/spec_test.rs
+++ b/tests/spec_test.rs
@@ -28,7 +28,7 @@ fn main() {
         let config_result = resolve_config(spec_config, &global_config);
         ensure_no_diagnostics(&config_result.diagnostics);
 
-        format_text(file_name, file_text.into(), &config_result.config)
+        format_text(file_name, None, file_text.into(), &config_result.config)
       })
     },
     Arc::new(move |_file_name, _file_text, _spec_config| {