chore(doc): Add an example of stripping out types (#2430)

Author: kdy1

ecmascript/transforms/typescript/examples/ts_to_js.rs

@@ -0,0 +1,79 @@
+//! Usage: cargo run --example ts_to_js path/to/ts
+//!
+//! This program will emit output to stdout.
+
+use std::{env, path::Path};
+use swc_common::{
+    self,
+    comments::SingleThreadedComments,
+    errors::{ColorConfig, Handler},
+    sync::Lrc,
+    SourceMap,
+};
+use swc_ecma_codegen::{text_writer::JsWriter, Emitter};
+use swc_ecma_parser::{lexer::Lexer, Parser, StringInput, Syntax, TsConfig};
+use swc_ecma_transforms_base::fixer::fixer;
+use swc_ecma_transforms_typescript::strip;
+use swc_ecma_visit::FoldWith;
+
+fn main() {
+    let cm: Lrc<SourceMap> = Default::default();
+    let handler = Handler::with_tty_emitter(ColorConfig::Auto, true, false, Some(cm.clone()));
+
+    // Real usage
+    // let fm = cm
+    //     .load_file(Path::new("test.js"))
+    //     .expect("failed to load test.js");
+
+    let input = env::args()
+        .nth(1)
+        .expect("please provide the path of input typescript file");
+
+    let fm = cm
+        .load_file(Path::new(&input))
+        .expect("failed to load input typescript file");
+
+    let comments = SingleThreadedComments::default();
+
+    let lexer = Lexer::new(
+        Syntax::Typescript(TsConfig {
+            tsx: input.ends_with(".tsx"),
+            dynamic_import: true,
+            ..Default::default()
+        }),
+        Default::default(),
+        StringInput::from(&*fm),
+        Some(&comments),
+    );
+
+    let mut parser = Parser::new_from(lexer);
+
+    for e in parser.take_errors() {
+        e.into_diagnostic(&handler).emit();
+    }
+
+    let module = parser
+        .parse_module()
+        .map_err(|e| e.into_diagnostic(&handler).emit())
+        .expect("failed to parse module.");
+
+    // Remove typescript types
+    let module = module.fold_with(&mut strip());
+
+    // Ensure that we have eenough parenthesis.
+    let module = module.fold_with(&mut fixer(Some(&comments)));
+
+    let mut buf = vec![];
+    {
+        let mut emitter = Emitter {
+            cfg: swc_ecma_codegen::Config { minify: false },
+            cm: cm.clone(),
+            comments: Some(&comments),
+            wr: JsWriter::new(cm.clone(), "\n", &mut buf, None),
+        };
+
+        emitter.emit_module(&module).unwrap();
+    }
+
+    println!("{}", String::from_utf8(buf).expect("non-utf8?"));
+}

ecmascript/transforms/typescript/src/strip.rs

@@ -94,6 +94,9 @@ pub fn strip_with_config(config: Config) -> impl Fold + VisitMut {
 }
 
 /// Strips type annotations out.
+///
+/// See the `examples` directory of the crate to see how you can transpile a
+/// typescript file to a javascript file.
 pub fn strip() -> impl Fold + VisitMut {
     strip_with_config(Default::default())
 }