如何在函数中使表达式仅在函数调用时第一次运行

I want to run this line of code run first time when function called this.totalVote = this.totalVote - 1; and after it when second time function run it should not run

我希望第一次运行这行代码时,函数名为this.totalVote = this.totalVote - 1;在第二次运行功能后,它不应该运行

downVote(eve){

      this.totalVote = this.totalVote - 1;
      if(this.ristricted === this.totalVote){
              this.totalVote = this.totalVote - 1;
      }else {

       }
  }

3 个解决方案

#1

Set a global variable to control whether or not to run that line:

设置一个全局变量来控制是否运行该行:

var downvoted = false;

downVote(eve){

      if(downvoted === false) {
        this.totalVote = this.totalVote - 1;
        downvoted = true;
      }

      if(this.ristricted === this.totalVote){
              this.totalVote = this.totalVote - 1;
      }else {

       }
  }

#2

If you want the function to keep some state (a calledBefore or callCount property, for example), you can just add a property to the function itself:

如果您希望函数保持某种状态(例如,calledBefore或callCount属性),您只需向函数本身添加一个属性:

function downVote(eve){
  if (!downVote.calledBefore) {
    downVote.calledBefore = true;
    // do one-time only stuff here:
    this.totalVote = this.totalVote - 1;
  }
  // do other stuff here:
  if(this.ristricted === this.totalVote){
     this.totalVote = this.totalVote - 1;
  }
}

Or you can wrap the function in a closure to hold the state privately:

或者您可以将函数包装在一个闭包中以私有地保存状态:

var downVote = (function (){
  var calledBefore = false;
  return function downVote(eve) {
    if (!calledBefore) {
      calledBefore = true;
      // do one-time only stuff here:
      this.totalVote = this.totalVote - 1;
    }
    // do other stuff here:
    if(this.ristricted === this.totalVote){
       this.totalVote = this.totalVote - 1;
    }
  }
})();

Demo of the latter:

演示后者:

    var downVote = (function (){
      var calledBefore = false;
      return function downVote(eve) {
        if (!calledBefore) {
          calledBefore = true;
          // do one-time only stuff here:
          console.log("First call");
        }
        // do other stuff here:
        console.log("Called");
      }
    })();

    downVote();
    downVote();
    downVote();

#3

I guess you could just add another variable to track if the function has been called?

我想你可以添加另一个变量来跟踪函数是否被调用?

this.downVoteCalled = false;

downVote(eve){

  if(!this.downVoteCalled){
    this.totalVote = this.totalVote - 1;
    this.downVoteCalled = true; 
  }

  if(this.ristricted === this.totalVote){
          this.totalVote = this.totalVote - 1;
  }else {

   }
}

#1