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注入this用来获取js运行时设置的属性 ​

在类中使用 ​

js
import { QueryEngine } from './index.js'
 
const qe = new QueryEngine()
qe.refCount = 3
console.log(qe.getRefCount()) // 3
import { QueryEngine } from './index.js'
 
const qe = new QueryEngine()
qe.refCount = 3
console.log(qe.getRefCount()) // 3

在上面的例子中， QueryEngine 并没有声明和初始化 refCount， 但是js动态设置了，rust要怎么做才能获取到这个属性呢？

rust
#[napi]
use napi::bindgen_prelude::*;
use napi_derive::napi;
 
pub struct QueryEngine {}
 
#[napi]
impl QueryEngine {
  #[napi(constructor)]
  pub fn new() -> Result<Self> {
    Ok(Self {})
  }
 
  #[napi]
  pub fn get_ref_count(&self, this: This) -> Result<Option<i32>> {
    this.get::<i32>("refCount")
  }
}
#[napi]
use napi::bindgen_prelude::*;
use napi_derive::napi;
 
pub struct QueryEngine {}
 
#[napi]
impl QueryEngine {
  #[napi(constructor)]
  pub fn new() -> Result<Self> {
    Ok(Self {})
  }
 
  #[napi]
  pub fn get_ref_count(&self, this: This) -> Result<Option<i32>> {
    this.get::<i32>("refCount")
  }
}

在函数中使用 ​

rust
import { Width, plusOne } from './index.js'
 
const width = new Width(1)
console.log(plusOne(width)) // 2
import { Width, plusOne } from './index.js'
 
const width = new Width(1)
console.log(plusOne(width)) // 2

在上面的例子中，plusOne可能有自己的this上下文

rust
use napi::bindgen_prelude::*;
use napi_derive::napi;
 
#[napi(constructor)]
pub struct Width {
  pub value: i32,
}
 
#[napi]
pub fn plus_one(this: This<&Width>) -> i32 {
  this.value + 1
}
use napi::bindgen_prelude::*;
use napi_derive::napi;
 
#[napi(constructor)]
pub struct Width {
  pub value: i32,
}
 
#[napi]
pub fn plus_one(this: This<&Width>) -> i32 {
  this.value + 1
}