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如何总是在函数结束时运行清理?

node.js javascript

Hatted Rooster · 技术社区 · 7 年前

假设我有这个函数(psuedo代码):

function Foo() {

  let varThatRequiresCleanup = //something

  if(condition1) {
    return Error1;
  }

  if(condition2) {
    return Error2;
  }

  if(condition3) {
    return Error3;
  }
  //etc.. more ifs and important code.

  varThatRequiresCleanup.CleanUp();
  return Success;
}

goto 但JavaScript两者都没有。

我该怎么打电话 CleanUp() 无论何时 Foo() 退货?

清理() if 我回来了?

5 回复 | 直到 7 年前

Dacre Denny 7 年前

通过这种方式,您可以通过以下方式实现所需:

function Foo() {

  let varThatRequiresCleanup = //something

  // Define your "actual" Foo logic in an inner function
  // where you can define your flow and return logic as 
  // needed.
  function InnerFoo() {

    // You can access variables in the Foo closure, like so
    console.log(varThatRequiresCleanup);

    if(condition1) {
      return Error1;
    }

    if(condition2) {
      return Error2;
    }

    if(condition3) {
      return Error3;
    }

    //etc.. more ifs and important code.
    return Success;
  }

  // Now call your inner function like so
  var result = InnerFoo();

  // Now you can cleanup resourced in scope of Foo as
  // in this way, because this line will be hit
  varThatRequiresCleanup.CleanUp();

  // Return the result from InnerFoo()
  return result;
}

Slai 7 年前

一种替代方法是对重复代码使用函数:

function Foo() {

  let varThatRequiresCleanup = //something

  function CleanUpAndReturn(returnValue) {
    varThatRequiresCleanup.CleanUp();
    return returnValue;
  }

  if (condition1) { return CleanUpAndReturn(Error1); }

  if (condition2) { return CleanUpAndReturn(Error2); }

  if (condition3) { return CleanUpAndReturn(Error3); }
  //etc.. more ifs and important code.

  return CleanUpAndReturn(Success);
}

Cepheus 7 年前

可以使用try finally块:

function Foo() {
  let varThatRequiresCleanup = //something

  try {
    if(condition1) {
      return Error1;
    }

    if(condition2) {
      return Error2;
    }

    if(condition3) {
      return Error3;
    }
    //etc.. more ifs and important code.

    return Success;
  } finally {
    varThatRequiresCleanup.CleanUp();
  }
}

agDev 7 年前

你可以做一个叫做猴子补丁的事情。

概念取自 here .

function foo(){
    if(condition1) {
        return Error1;
    }

    if(condition2) {
        return Error2;
    }

    if(condition3) {
        return Error3;
    }
}

var tempFoo = foo;

window.foo = function() {
    tempFoo();

    //do the cleanup here
    CleanUp();
}

Get Off My Lawn 7 年前

它通过返回 new Proxy get

创建返回新代理的实例
1. 代理将立即拦截并处理调用
2. 代理将像以前一样运行函数
3. 然后代理将运行cleanup函数

class MyClass {

  constructor() {
    this.varThatRequiresCleanup = null
    // Create a reference to `this` so the function below can use it
    let $this = this
    
    // A private function this will clean stuff up
    // We can't use `this` in this function because it references window
    // We will use our reference `$this` instead
    function cleanup() {
      $this.varThatRequiresCleanup = null
      console.log('cleaned up')
    }

    // Create a proxy that will handle the method calls
    return new Proxy(this, {
      get: (target, prop, receiver) => {
        // Get the called property
        let targetValue = Reflect.get(target, prop, receiver)
        // Execute the called property
        return (...args) => {
          let r = targetValue.apply(this, args)
          console.log('before varThatRequiresCleanup:', this.varThatRequiresCleanup)
          cleanup()
          console.log('after varThatRequiresCleanup:', this.varThatRequiresCleanup)
          return r
        }
      }
    })
  }

  Foo() {
    this.varThatRequiresCleanup = 'foo'
    return 'foo result'
  }

  Bar() {
    this.varThatRequiresCleanup = 'bar'
    return 'bar result'
  }
}

let c = new MyClass()
console.log('Foo Return Value:', c.Foo())
console.log('-----------')
console.log('Bar Return Value:', c.Bar())