Construct the function name with concatenation

Question

How can I make something like that:

var string1 = "functionNameBeginning";
var string2 = "functionNameEnding";

element.innerHTML = string1 + string2 //string1 + string2 is name of function to execute

UPD: The thing that I wanted is to execute the function which is named string1string2(), and the user Spencer Wieczorek understood me right in his comment about eval() function. Also I really have found a better idea to solve this problem. Since it was the way that I wanted to use for processing select input's value on Wordpress site:

<select name="formula" class="left-input" id="formula">
    <option value="mifflin" selected>Mifflin-St Jeor</option>
    <option value="harris">Harris–Benedict</option>
    <option value="katch">Katch-McArdle</option>
</select>

I've written the function in my WP plugin:

if ($_POST['formula'] == 'mifflin') {
    return mifflinFormula();
} else if ($_POST['formula'] == 'harris') {
    return harrisFormula();
} else {
    return katchFormula($_POST['fat']);
}

@Leo240 So would you be wanting to do something like: `eval(string1 + string2 + "()");`? — Spencer Wieczorek, Mar 31 '16 at 08:10
If you choose to use eval, do refer following post first: http://stackoverflow.com/questions/86513/why-is-using-the-javascript-eval-function-a-bad-idea — Rajesh, Mar 31 '16 at 08:13
@SpencerWieczorek Thanks for your help, I've updated my question and described the solution that I've made. I hope that there is all clear now. — Leo240, Nov 30 '17 at 09:45

Rayon · Answer 1 · 2016-03-31T08:06:58.360

If function are declared in global(window) scope, you can access them as key of window using bracket notation as you are using variable as key

function functionNameBeginning() {
  return 'Hi...';
}

function functionNameEnding() {
  return 'Bye...';
}
var string1 = "functionNameBeginning";
var string2 = "functionNameEnding";
var element = document.body;
element.innerHTML = window[string1]() + window[string2]();

Edit:

If you have a function name which is being formed after concatenating values returned from first 2 functions, you could so it this way. But I would suggest you to use your own object having property-values as functions.

function functionNameBeginning() {
  return 'Hi';
}

function functionNameEnding() {
  return 'Bye';
}

function HiBye() {
  return 'Hi...Bye executed!';
}
var string1 = "functionNameBeginning";
var string2 = "functionNameEnding";
var element = document.body;
element.innerHTML = window[window[string1]() + window[string2]()]();

While the question is unclear, I don't think this is what they are looking for. It seems they want to execute a function based on it's name given by a concatenated string. — Spencer Wieczorek, Mar 31 '16 at 08:04
@SpencerWieczorek, I guess I am making mess of it..Is edit valid under the asked context ? — Rayon, Mar 31 '16 at 08:07

score 0 · Answer 2 · answered Mar 31 '16 at 07:58

0

Are you trying to execute an arbitrary function, or one you have control over how it's defined?

If it's arbitrary you might be heading down a dangerous path since you need to use eval to execute it, and that's always risky.

If it's under your control, try this:

var functions = {
   example_a: function() {
   },
   test_b: function() {
   }
};

functions["example" + "_" + "a"]();

answered Mar 31 '16 at 07:58

tadman

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I have a few functions with names those end with "Formula()" and first part of name is from "data-param" – Leo240 Mar 31 '16 at 08:02
If the variables are only under the programmers control then I don't think using `eval()` is risky. – Spencer Wieczorek Mar 31 '16 at 08:07
@Leo240 are you trying to bind this function to element? If yes, you should try `addEventListener("event", window[functionName])`. [Sample Fiddle](https://jsfiddle.net/RajeshDixit/4c7mjw25/) – Rajesh Mar 31 '16 at 08:11

Construct the function name with concatenation

2 Answers2