how to detect a function was called with javascript_问答_开发者

how to detect a function was called with javascript

开发者 https://www.devze.com 2023-01-09 07:56 出处：网络

I have a ja开发者_开发百科vascript function. How to check: if function was called ( in <head></head> section have this function), then not to call the function

相关专题：aop javascript

I have a ja开发者_开发百科vascript function.

How to check:

if function was called ( in <head></head> section have this function), then not to call the function
if function was not called ( in <head></head> section haven't this function), then call the function

like require_once or include_once with PHP

Static variables

Here's how to create static (like in C) variables using self calling functions to store your static variables in a closure.

var myFun = (function() {
  var called = false;
  return function() {
    if (!called) {
      console.log("I've been called");
      called = true;
    }
  }
})()

Abstract the idea

Here's a function that returns a function that only gets called once, this way we don't have to worry about adding boiler plate code to every function.

function makeSingleCallFun(fun) {
  var called = false;
  return function() {
    if (!called) {
      called = true;
      return fun.apply(this, arguments);
    }
  }
}

var myFun = makeSingleCallFun(function() {
  console.log("I've been called");
});

myFun(); // logs I've been called
myFun(); // Does nothing

Use decorator pattern.

// your function definition
function yourFunction() {}

// decorator
function callItOnce(fn) {
    var called = false;
    return function() {
        if (!called) {
            called = true;
            return fn();
        }
        return;
    }
}

yourFunction(); // it runs
yourFunction(); // it runs    
yourFunction = callItOnce(yourFunction);
yourFunction(); // it runs
yourFunction(); // null

This solution provides a side-effect free way for achieving your goal. You don't have to modify your original function. It works nice even with library functions. You may assign a new name to the decorated function to preserve the original function.

var myLibraryFunction = callItOnce(libraryFunction);
myLibraryFunction(); // it runs
myLibraryFunction(); // null
libraryFunction(); // it runs

var called = false;
function blah() {
   called = true;
}

if ( !called ) {
   blah();
}

You can use a global variable in a custom namespace to store whether the function has been called.

if(!window.mynamespace){
    window.mynamespace={};
}

mynamespace.callMeOnlyOnce=function(){

    if(mynamespace.alreadyCalled)return;

    alert('calling for the first time');
    mynamespace.alreadyCalled=true;
};

// alert box comes
mynamespace.callMeOnlyOnce();


// no alert box
mynamespace.callMeOnlyOnce();

If (!your_func.called) {
    your_func.called = true;
    your_func();
}

how to detect a function was called with javascript

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