# `indexing_getter`, `indexing_setter`, and `indexing_deleter`
These three attributes indicate that a method is an dynamically intercepted
getter, setter, or deleter on the receiver object itself, rather than a direct
access of the receiver's properties. It is equivalent calling the Proxy handler
for the `obj[prop]` operation with some dynamic `prop` variable in JavaScript,
rather than a normal static property access like `obj.prop` on a normal
JavaScript `Object`.
This is useful for binding to `Proxy`s and some builtin DOM types that
dynamically intercept property accesses.
* `indexing_getter` corresponds to `obj[prop]` operation in JavaScript. The
function annotated must have a `this` receiver parameter, a single parameter
that is used for indexing into the receiver (`prop`), and a return type.
* `indexing_setter` corresponds to the `obj[prop] = val` operation in
JavaScript. The function annotated must have a `this` receiver parameter, a
parameter for indexing into the receiver (`prop`), and a value parameter
(`val`).
* `indexing_deleter` corresponds to `delete obj[prop]` operation in
JavaScript. The function annotated must have a `this` receiver and a single
parameter for indexing into the receiver (`prop`).
These must always be used in conjunction with the `structural` and `method`
flags.
For example, consider this JavaScript snippet that uses `Proxy`:
```js
const foo = new Proxy({}, {
get(obj, prop) {
return prop in obj ? obj[prop] : prop.length;
},
set(obj, prop, value) {
obj[prop] = value;
},
deleteProperty(obj, prop) {
delete obj[prop];
},
});
foo.ten;
// 3
foo.ten = 10;
foo.ten;
// 10
delete foo.ten;
foo.ten;
// 3
```
To bind that in `wasm-bindgen` in Rust, we would use the `indexing_*` attributes
on methods:
```rust
#[wasm_bindgen]
extern "C" {
type Foo;
static foo: Foo;
#[wasm_bindgen(method, structural, indexing_getter)]
fn get(this: &Foo, prop: &str) -> u32;
#[wasm_bindgen(method, structural, indexing_setter)]
fn set(this: &Foo, prop: &str, val: u32);
#[wasm_bindgen(method, structural, indexing_deleter)]
fn delete(this: &Foo, prop: &str);
}
assert_eq!(foo.get("ten"), 3);
foo.set("ten", 10);
assert_eq!(foo.get("ten"), 10);
foo.delete("ten");
assert_eq!(foo.get("ten"), 3);
```