Modernize code examples in guide (mostly remove extern crate) (#2233)

Author: Veetaha

guide/src/contributing/js-sys/index.md

@@ -19,8 +19,6 @@ time how long they take to execute with [`Date.now()`][mdn-date-now], and we
 don't need to write any JS imports ourselves:
 
 ```rust
-extern crate js_sys;
-extern crate wasm_bindgen;
 use wasm_bindgen::prelude::*;
 
 #[wasm_bindgen]

guide/src/reference/arbitrary-data-with-serde.md

@@ -14,22 +14,8 @@ To enable the `"serde-serialize"` feature, do two things in `Cargo.toml`:
 
 ```toml
 [dependencies]
-serde = "^1.0.59"
-serde_derive = "^1.0.59"
-
-[dependencies.wasm-bindgen]
-version = "^0.2"
-features = ["serde-serialize"]
-```
-
-## Import Serde's Custom-Derive Macros
-
-In your top-level Rust file (e.g. `lib.rs` or `main.rs`), enable the `Serialize`
-and `Deserialize` custom-derive macros:
-
-```rust
-#[macro_use]
-extern crate serde_derive;
+serde = { version = "1.0", features = ["derive"] }
+wasm-bindgen = { version = "0.2", features = ["serde-serialize"] }
 ```
 
 ## Derive the `Serialize` and `Deserialize` Traits
@@ -46,7 +32,9 @@ ABI naively, but all of them implement Serde's `Serialize` and `Deserialize`.
 Note that we do not need to use the `#[wasm_bindgen]` macro.
 
 ```rust
-#[derive(Serialize)]
+use serde::{Serialize, Deserialize};
+
+#[derive(Serialize, Deserialize)]
 pub struct Example {
     pub field1: HashMap<u32, String>,
     pub field2: Vec<Vec<f32>>,
@@ -100,7 +88,7 @@ import { send_example_to_js, receive_example_from_js } from "example";
 let example = send_example_to_js();
 
 // Add another "Vec" element to the end of the "Vec<Vec<f32>>"
-example.field2.push([5,6]);
+example.field2.push([5, 6]);
 
 // Send the example object back to wasm.
 receive_example_from_js(example);

guide/src/reference/iterating-over-js-values.md

@@ -27,8 +27,6 @@ Rust iterator will yield items of type `Result<JsValue>`. If it yields an
 `Err(...)`, then the JS iterator protocol threw an exception.
 
 ```rust
-extern crate js_sys;
-extern crate wasm_bindgen;
 use wasm_bindgen::prelude::*;
 
 #[wasm_bindgen]
@@ -67,8 +65,6 @@ For example, we can write a function that collects the numbers from any JS
 iterable and returns them as an `Array`:
 
 ```rust
-extern crate js_sys;
-extern crate wasm_bindgen;
 use wasm_bindgen::prelude::*;
 
 #[wasm_bindgen]

guide/src/reference/receiving-js-closures-in-rust.md

@@ -8,9 +8,6 @@ For example, we can wrap a `Vec<u32>` in a new type, export it to JavaScript,
 and invoke a JavaScript closure on each member of the `Vec`:
 
 ```rust
-extern crate js_sys;
-extern crate wasm_bindgen;
-
 use wasm_bindgen::prelude::*;
 
 #[wasm_bindgen]
@@ -21,8 +18,8 @@ pub struct VecU32 {
 #[wasm_bindgen]
 impl VecU32 {
     pub fn each(&self, f: &js_sys::Function) {
-        let this = JsValue::NULL;
-        for x in &self.xs {
+        let this = JsValue::null();
+        for &x in &self.xs {
             let x = JsValue::from(x);
             let _ = f.call1(&this, &x);
         }

guide/src/wasm-bindgen-test/usage.md

@@ -16,7 +16,6 @@ older compilers use the `0.2.*` track of `wasm-bindgen-test`.
 Create a `$MY_CRATE/tests/wasm.rs` file:
 
 ```rust
-extern crate wasm_bindgen_test;
 use wasm_bindgen_test::*;
 
 #[wasm_bindgen_test]

guide/src/web-sys/using-web-sys.md

@@ -37,9 +37,6 @@ features = [
 ## Call the method!
 
 ```rust
-extern crate web_sys;
-extern crate wasm_bindgen;
-
 use wasm_bindgen::prelude::*;
 use web_sys::Window;