Javascript运行代码一次

Question

I only want my JavaScript to run once, but I cannot control how many times the javascript file is executed. Basically I'm writing a tiny JS snippet into a CMS, and the CMS is actually calling it 5-10 times. So solutions like this:

function never_called_again(args) {
  // do some stuff
  never_called_again = function (new_args) {
   // do nothing
  }
}
never_called_again();

Don't seem to work because as soon as my snippet is run again from the top the function is re-declared, and 'do some stuff' is re-evaluated. Perhaps I'm just not doing it properly, I'm not great with JS. I'm considering using something like try-catch on a global variable, something like

if (code_happened == undefined) {
    \\ run code
     code_happened = true;
}

EDIT: There is a consistent state eg if I set a variable I can see when my snippet is run again. But having to declare it before I access it, I don't know how to say 'does this variable exist yet'

Answer 1

Try this:

var doneTheStuff;
function whatever() {
  if (!doneTheStuff) {
    doneTheStuff = true;
    // do the stuff
  }
}

Redundant variable declarations don't affect the value of the variable. Once one of the functions has set the variable to true , the others won't do anything.

Answer 2

if (typeof code_happened === 'undefined') {
  window.code_happened = true;
  // Your code here.
}

The typeof check gets you around the fact that the global hasn't been declared. You could also just do if (!window.code_happened) since property access isn't banned for undefined properties.

Answer 3

Use a closure, and set a flag. If the flag is true , just return:

if ( ! window.never_called_again  ) {
    window.never_called_again = (function () {
        var ran = false;
        return function (args) {
            if ( ran ) return;
            ran = true;
            // Do stuff
        };
    }());
}

Here's the fiddle: http://jsfiddle.net/U2NCs/

Answer 4

With jQuery, the function .one() may be useful : http://api.jquery.com/one/

W3School exemple here : http://www.w3schools.com/jquery/event_one.asp

Answer 5

In this way, the code is executed only once.

if(typeof onceRun == "undefined") window.onceRun=(
    ()=>{
        //your codes...
        console.log("runing...")
    return true
    }).call()