如何只调用一次函数？

Question

How can I call the function only for once?

var myFunction = function () {
    alert("calling function only for once");
}
myFunction();//alert "calling function only for once"
myFunction();//should not alert // if I call multiple times this should not be called

Answer 1

Try this:

var myFunction = function () {
    alert("calling function only for once");
    myFunction = function(){
        return false;
    }
}
myFunction();//alert "calling function only for once"
myFunction();//should not alert

Answer 2

在运行函数时将一些goobal变量存储为一个标志，并在函数启动时检查该变量。

Answer 3

set a flag, and call according to that flag:

var IsAlreadyCalled=false;
var myFunction = function () {
   if(!IsAlreadyCalled){
      alert("calling function only for once");
      IsAlreadyCalled = true;
   }
}
myFunction();//alert "calling function only for once"
myFunction();//should not alert

Answer 4

In your very odd scenario , the easiest way is to set a boolean:

var run = true,
    myFunction = function(){
        if(run){
            alert('calling function only for once');
            run = false;
        } else {
            return false;
        }
    };

myFunction(); // will run
myFunction(); // won't run

That way later on if you need to "reactivate" it you can just set the boolean back to true and call it again.

run = true;
myFunction(); // will run again

Answer 5

Other suggestions of using a flag are fine, but I would build it as a function decorator, that you can apply to any function. You avoid global variables this way, and your code becomes more readable and reusable:

// Takes a function and returns a function
// that executes only once
function once(f) {
  var flag;
  return function() {
    if (!flag) {
      flag = true;
      return f.apply(this, arguments);
    }
  };
}

var fn = once(function() {
  console.log('logged!');
});

fn(); // logged!
fn();
fn();

Demo: http://jsbin.com/povu/1/edit