how to conditionally include or exclude statements from function expression

Question

i have 2 different javascript environments and want to create a library usable on both. to do that i want to use higher order functions to generate my functions, like so

    try {
      Maptool.chat.broadcast("")
      var myFunc1 = genFunction1("env1");
    }
    catch(e){
      if(e instanceof ReferenceError){
        var myFunc1 = genFunction1("env2")
      }
    }

genFunction1 would return a function that i could call built from a function expression. there are only 2 ways i know to generate the function that is returned, it could be written similarly to the next code block with the if outside the inner function which would create a lot of code duplication as i would need to write everything in the function that is unchanged again.

     function genFunction1(env){
       if(env == "env1"){
         return function () {return 3;}
       }
       else{
         return function () {return 2;}
       }  
     }

or with the if inside like the following code block

    genFunction1(env){
      return function (){
        if(env=="env1"){
          return 3;
        }
        return 2;
      }
    }

however if we use a object with a get property which logs when accessed we can see that the third code block calls a if for each call of myFunc1.

    function genFunc1(obj){
      return function (){
        if(obj.env == "env2"){
            console.log("3");
        }
        console.log("2");
      }
    }
    const obj = {
      get env() {
        console.log("accessed property");
        return "env2";
      }
    }
    var myFunc1 = genFunc1(obj);
    myFunc1();
    myFunc1();

as previously said the earlier code block calls the get method once for each call of myFunc1(),but the environment won't change aside from the first time i check, is there any way to make the generated function not include a if and include the if only in the higher order function without duplicating code?

It probably doesn't matter. If the function really is executed often enough for this to matter, the optimising compile will realise that `env=="env1"` is a constant and not evaluate it every time. — Bergi, Jun 22 '22 at 14:26
There's not a lot code in your function. Can you show us your actual code, please, so that we can help with actually avoiding some code duplication? — Bergi, Jun 22 '22 at 14:26

score 0 · Answer 1 · answered Jun 22 '22 at 14:30

This is expected behavior as you are getting property from an object. Take a snapshot of the value before generating the function, like this.

function genFunc1(obj) {
  var env = obj.env
  return function() {
    if (env == "env2") {
      console.log("3");
    }
    console.log("2");
  }
}

how to conditionally include or exclude statements from function expression

1 Answers1