Question

我试图记录输入参数和方法调用的返回值。

class A {
    constructor () {
        this.x = 'x'
    }

    callinstance(x){
        // i want to log above value of x without changing class code
        if (typeof this.x !== 'string') throw new Error('this.x MUST_BE_STRING')
        return x + 1
        // i want to log value to be returned without changing code
    }
}

A.callstatic = function(x){
    // i want to log above value of x without changing class code
    return x + 2
    // i want to log value to be returned without changing code
}

A.a = 'a' // a static property should't be touched

// i can't change above code. i also cannot put a log in the actual methods

// now here is the soution, but runs into stack overflow. For obvious reasons.
const instrument = function(prop, static) {
  return function (...args) {
      if (!static) static = this      
      console.log(args) // here instrumenting inputs
      const t = static[prop](...args)
      console.log(t) // here instrumenting return values
      return t
  }
}

// overriding all the static methods
Object.getOwnPropertyNames(A).filter(p => typeof A[p] === 'function').forEach((prop) => {
  A[prop] = instrument(prop, A)
})
// overriding all the instance methods
Object.getOwnPropertyNames(A.prototype).filter(p => typeof A.prototype[p] === 'function' && p !== 'constructor').forEach((prop) => {
  A.prototype[prop] = instrument(prop)
})


// validation
console.log(A.callstatic(1))
console.log((new A()).callinstance(11))
console.log(A.a)

以上解决方案由于明显的原因而进入堆栈溢出。有什么解决方法可以实现我的目标？无需更改班级代码？

PS：这不是家庭作业，我只是想知道一种调试工具的解决方案。

Answer 1

您的问题是堆栈溢出错误，因为您要覆盖自己的方法这意味着

/*
A[prop] = instrument(prop, A);  <-- this turns into as followed (replacing A[prop] to method name)

function callinstance = () {
      console.log(args) // here instrumenting inputs
      const t = callinstance(...args) // <-- recursion happens here
      console.log(t) /
}

您可以做一些变通办法来解决此问题，创建该函数的副本，并覆盖您的自定义函数中的类方法，请在 oldMethod

中调用

// overriding all the static methods
Object.getOwnPropertyNames(A).filter(p => typeof A[p] === 'function').forEach((prop) => {
    let oldMethod = A[prop];
    A[prop] = function(args) {
                    console.log(args);
                    let x = oldMethod(args);
                    console.log(x);
                };
})

// overriding all the instance methods
Object.getOwnPropertyNames(A.prototype).filter(p => typeof A.prototype[p] === 'function' && p !== 'constructor').forEach((prop) => {
    let oldMethod = A.prototype[prop];
    A.prototype[prop] = function(...args) {
                    console.log(...args);
                    let x = oldMethod.call(this, ...args);
                    console.log(x);
                };
})

检测参数以及类的静态方法和实例方法的返回值

1 个答案: