The js_name attribute can be used to bind to a different function in JavaScript than the identifier that's defined in Rust.

Most often, this is used to convert a camel-cased JavaScript identifier into a snake-cased Rust identifier:

# #![allow(unused_variables)]
#fn main() {
#[wasm_bindgen]
extern "C" {
    #[wasm_bindgen(js_name = jsOftenUsesCamelCase)]
    fn js_often_uses_camel_case() -> u32;
}
#}

Sometimes, it is used to bind to JavaScript identifiers that are not valid Rust identifiers, in which case js_name = "some string" is used instead of js_name = ident:

# #![allow(unused_variables)]
#fn main() {
#[wasm_bindgen]
extern "C" {
    #[wasm_bindgen(js_name = "$$$")]
    fn cash_money() -> u32;
}
#}

However, you can also use js_name to define multiple signatures for polymorphic JavaScript functions:

# #![allow(unused_variables)]
#fn main() {
#[wasm_bindgen]
extern "C" {
    #[wasm_bindgen(js_namespace = console, js_name = log)]
    fn console_log_str(s: &str);

    #[wasm_bindgen(js_namespace = console, js_name = log)]
    fn console_log_u32(n: u32);

    #[wasm_bindgen(js_namespace = console, js_name = log)]
    fn console_log_many(a: u32, b: &JsValue);
}
#}

All of these functions will call console.log in JavaScript, but each identifier will have only one signature in Rust.

Note that if you use js_name when importing a type you'll also need to use the js_class attribute when defining methods on the type:

# #![allow(unused_variables)]
#fn main() {
#[wasm_bindgen]
extern "C" {
    #[wasm_bindgen(js_name = String)]
    type JsString;
    #[wasm_bindgen(method, getter, js_class = "String")]
    pub fn length(this: &JsString) -> u32;
}
#}

The js_name attribute can also be used in situations where a JavaScript module uses export default. In this case, setting the js_name attribute to "default" on the type declaration, and the js_class attribute to "default" on any methods on the exported object will generate the correct imports.

For example, a module that would be imported directly in JavaScript:

import Foo from "bar";

let f = new Foo();

Could be accessed using this definition in Rust:

# #![allow(unused_variables)]
#fn main() {
#[wasm_bindgen(module = "bar")]
extern "C" {
    #[wasm_bindgen(js_name = default)]
    type Foo;
    #[wasm_bindgen(constructor, js_class = default)]
    pub fn new() -> Foo;
}
#}