Fix the constructor explanation in the guide (#372)

examples/smorgasboard/app.js

@@ -8,16 +8,16 @@ function assertEq(a, b) {
 
 assertEq(concat('a', 'b'), 'ab');
 
-// Note the `new Foo()` syntax cannot be used, static function
+// Note that to use `new Foo()` the constructor function must be annotated
-// constructors must be used instead. Additionally objects allocated
+// with `#[wasm_bindgen(constructor)]`, otherwise only `Foo.new()` can be used.
-// corresponding to Rust structs will need to be deallocated on the
+// Additionally objects allocated corresponding to Rust structs will need to
-// Rust side of things with an explicit call to `free`.
+// be deallocated on the Rust side of things with an explicit call to `free`.
-let foo = Foo.new();
+let foo = new Foo();
 assertEq(foo.add(10), 10);
 foo.free();
 
 // Pass objects to one another
-let foo1 = Foo.new();
+let foo1 = new Foo();
 let bar = Bar.from_str("22", { opaque: 'object' });
 foo1.add_other(bar);
 

examples/smorgasboard/src/lib.rs

@@ -21,6 +21,7 @@ pub struct Foo {
 
 #[wasm_bindgen]
 impl Foo {
+    #[wasm_bindgen(constructor)]
     pub fn new() -> Foo {
         Foo { contents: 0 }
     }

guide/src/what-else-can-we-do.md

@@ -27,6 +27,7 @@ pub struct Foo {
 
 #[wasm_bindgen]
 impl Foo {
+    #[wasm_bindgen(constructor)]
     pub fn new() -> Foo {
         Foo { contents: 0 }
     }
@@ -110,16 +111,16 @@ function assertEq(a, b) {
 function main() {
   assertEq(concat('a', 'b'), 'ab');
 
-  // Note the `new Foo()` syntax cannot be used, static function
+  // Note that to use `new Foo()` the constructor function must be annotated
-  // constructors must be used instead. Additionally objects allocated
+  // with `#[wasm_bindgen(constructor)]`, otherwise only `Foo.new()` can be used.
-  // corresponding to Rust structs will need to be deallocated on the
+  // Additionally objects allocated corresponding to Rust structs will need to
-  // Rust side of things with an explicit call to `free`.
+  // be deallocated on the Rust side of things with an explicit call to `free`.
-  let foo = Foo.new();
+  let foo = new Foo();
   assertEq(foo.add(10), 10);
   foo.free();
 
   // Pass objects to one another
-  let foo1 = Foo.new();
+  let foo1 = new Foo();
   let bar = Bar.from_str("22", { opaque: 'object' });
   foo1.add_other(bar);