How to execute a JavaScript function when I have its name as a string

Question

I have the name of a function in JavaScript as a string. How do I convert that into a function pointer so I can call it later?

Depending on the circumstances, I may need to pass various arguments into the method too.

Some of the functions may take the form of namespace.namespace.function(args[...]).

Answer 1

Don't use eval unless you absolutely, positively have no other choice.

As has been mentioned, using something like this would be the best way to do it:

window["functionName"](arguments);

That, however, will not work with a namespace'd function:

window["My.Namespace.functionName"](arguments); // fail

This is how you would do that:

window["My"]["Namespace"]["functionName"](arguments); // succeeds

In order to make that easier and provide some flexibility, here is a convenience function:

function executeFunctionByName(functionName, context /*, args */) {
  var args = Array.prototype.slice.call(arguments, 2);
  var namespaces = functionName.split(".");
  var func = namespaces.pop();
  for(var i = 0; i < namespaces.length; i++) {
    context = context[namespaces[i]];
  }
  return context[func].apply(context, args);
}

You would call it like so:

executeFunctionByName("My.Namespace.functionName", window, arguments);

Note, you can pass in whatever context you want, so this would do the same as above:

executeFunctionByName("Namespace.functionName", My, arguments);

Answer 2

Just thought I'd post a slightly altered version of Jason Bunting's very helpful function.

First, I have simplified the first statement by supplying a second parameter to slice(). The original version was working fine in all browsers except IE.

Second, I have replaced this with context in the return statement; otherwise, this was always pointing to window when the target function was being executed.

function executeFunctionByName(functionName, context /*, args */) {
    var args = Array.prototype.slice.call(arguments, 2);
    var namespaces = functionName.split(".");
    var func = namespaces.pop();
    for (var i = 0; i < namespaces.length; i++) {
        context = context[namespaces[i]];
    }
    return context[func].apply(context, args);
}

Answer 3

The answer to this other question shows you how to do that: Javascript equivalent of Python's locals()?

Basically, you can say

window["foo"](arg1, arg2);

or as many others have suggested, you can just use eval:

eval(fname)(arg1, arg2);

although this is extremely unsafe unless you're absolutely sure about what you're eval-ing.

Answer 4

I think an elegant way of doing this is by defining your functions in a hash object. Then you can have a reference to those functions from the hash using the string. e.g.

var customObject = {
  customFunction: function(param){...}
};

Then you can call:

customObject['customFunction'](param);

Where customFunction will be a string matching a function defined in your object.

UPDATE

It seems that this answer was helpful for many fellow coders out there so here goes an updated version.

With ES6 you can additionally use Computed Property Names which will allow you to avoid magic strings.

const FunctionNames = Object.freeze({ 
  FirstFunction: "firstFunction", 
  SecondFunction: "secondFunction" 
});

...

var customObject = {
  [FunctionNames.FirstFunction]: function(param){...},
  [FunctionNames.SecondFunction]: function(param){...}
};

...

customObject[FunctionNames.FirstFunction](param);

Answer 5

Could you not just do this:

var codeToExecute = "My.Namespace.functionName()";
var tmpFunc = new Function(codeToExecute);
tmpFunc();

You can also execute any other JavaScript using this method.

Answer 6

With ES6 you could to access class methods by name:

class X {
  method1(){
    console.log("1");
  }
  method2(){
    this['method1']();
    console.log("2");
  }
}
let x  = new X();
x['method2']();

the output would be:

1
2

Answer 7

Two things:

• avoid eval, it's terribly dangerous and slow

• secondly it doesn't matter where your function exists, "global" -ness is irrelevant. x.y.foo() can be enabled through x.y['foo']() or x['y']['foo']() or even window['x']['y']['foo'](). You can chain indefinitely like this.

Answer 8

All the answers assume that the functions can be accessed through global scope (window). However, the OP did not make this assumption.

If the functions live in a local scope (aka closure) and are not referenced by some other local object, bad luck: You have to use eval() AFAIK, see dynamically call local function in javascript

Answer 9

Depending on where you are you can also use:

this["funcname"]();
self["funcname"]();
window["funcname"]();
top["funcname"]();
globalThis["funcname"]();

or, in nodejs

global["funcname"]()

Answer 10

Here is my contribution to Jason Bunting's / Alex Nazarov's excellent answers, where I include error checking requested by Crashalot.

Given this (contrived) preamble:

a = function( args ) {
    console.log( 'global func passed:' );
    for( var i = 0; i < arguments.length; i++ ) {
        console.log( '-> ' + arguments[ i ] );
    }
};
ns = {};
ns.a = function( args ) {
    console.log( 'namespace func passed:' );
    for( var i = 0; i < arguments.length; i++ ) {
        console.log( '-> ' + arguments[ i ] ); 
    }
};
name = 'nsa';
n_s_a = [ 'Snowden' ];
noSuchAgency = function(){};

then the following function:

function executeFunctionByName( functionName, context /*, args */ ) {
    var args, namespaces, func;

    if( typeof functionName === 'undefined' ) { throw 'function name not specified'; }

    if( typeof eval( functionName ) !== 'function' ) { throw functionName + ' is not a function'; }

    if( typeof context !== 'undefined' ) { 
        if( typeof context === 'object' && context instanceof Array === false ) { 
            if( typeof context[ functionName ] !== 'function' ) {
                throw context + '.' + functionName + ' is not a function';
            }
            args = Array.prototype.slice.call( arguments, 2 );

        } else {
            args = Array.prototype.slice.call( arguments, 1 );
            context = window;
        }

    } else {
        context = window;
    }

    namespaces = functionName.split( "." );
    func = namespaces.pop();

    for( var i = 0; i < namespaces.length; i++ ) {
        context = context[ namespaces[ i ] ];
    }

    return context[ func ].apply( context, args );
}

will allow you to call a javascript function by name stored in a string, either namespaced or global, with or without arguments (including Array objects), providing feedback on any errors encountered (hopefully catching them).

The sample output shows how it works:

// calling a global function without parms
executeFunctionByName( 'a' );
  /* OUTPUT:
  global func passed:
  */

// calling a global function passing a number (with implicit window context)
executeFunctionByName( 'a', 123 );
  /* OUTPUT:
  global func passed:
  -> 123
  */

// calling a namespaced function without parms
executeFunctionByName( 'ns.a' );
  /* OUTPUT:
  namespace func passed:
  */

// calling a namespaced function passing a string literal
executeFunctionByName( 'ns.a', 'No Such Agency!' );
  /* OUTPUT:
  namespace func passed:
  -> No Such Agency!
  */

// calling a namespaced function, with explicit context as separate arg, passing a string literal and array 
executeFunctionByName( 'a', ns, 'No Such Agency!', [ 007, 'is the man' ] );
  /* OUTPUT:
  namespace func passed:
  -> No Such Agency!
  -> 7,is the man
  */

// calling a global function passing a string variable (with implicit window context)
executeFunctionByName( 'a', name );
  /* OUTPUT:
  global func passed:
  -> nsa
  */

// calling a non-existing function via string literal
executeFunctionByName( 'n_s_a' );
  /* OUTPUT:
  Uncaught n_s_a is not a function
  */

// calling a non-existing function by string variable
executeFunctionByName( n_s_a );
  /* OUTPUT:
  Uncaught Snowden is not a function
  */

// calling an existing function with the wrong namespace reference
executeFunctionByName( 'a', {} );
  /* OUTPUT:
  Uncaught [object Object].a is not a function
  */

// calling no function
executeFunctionByName();
  /* OUTPUT:
  Uncaught function name not specified
  */

// calling by empty string
executeFunctionByName( '' );
  /* OUTPUT:
  Uncaught  is not a function
  */

// calling an existing global function with a namespace reference
executeFunctionByName( 'noSuchAgency', ns );
  /* OUTPUT:
  Uncaught [object Object].noSuchAgency is not a function
  */

Answer 11

You just need convert your string to a pointer by window[<method name>]. example:

var function_name = "string";
function_name = window[function_name];

and now you can use it like a pointer.

Answer 12

Here is my Es6 approach which enables you to call your function by it's name as string or it's function name and also enable you to pass different numbers of arguments to different types of functions:

function fnCall(fn, ...args)
{
  let func = (typeof fn =="string")?window[fn]:fn;
  if (typeof func == "function") func(...args);
  else throw new Error(`${fn} is Not a function!`);
}


function example1(arg1){console.log(arg1)}
function example2(arg1, arg2){console.log(arg1 + "  and   " + arg2)}
function example3(){console.log("No arguments!")}

fnCall("example1", "test_1");
fnCall("example2", "test_2", "test3");
fnCall(example3);
fnCall("example4"); // should raise an error in console

Answer 13

If you want to call a function of an object instead of a global function with window["functionName"]. You can do it like;

var myObject=new Object();
myObject["functionName"](arguments);

Example:

var now=new Date();
now["getFullYear"]()

Answer 14

BE CAREFUL!!!

One should try to avoid calling a function by string in JavaScript for two reasons:

Reason 1: Some code obfuscators will wreck your code as they will change the function names, making the string invalid.

Reason 2: It is much harder to maintain code that uses this methodology as it is much harder to locate usages of the methods called by a string.

Answer 15

I don't think you need complicated intermediate functions or eval or be dependent on global variables like window:

function fun1(arg) {
  console.log(arg);
}

function fun2(arg) {
  console.log(arg);
}

const operations = {
  fun1,
  fun2
};

operations["fun1"]("Hello World");
operations.fun2("Hello World");

// You can use intermediate variables, if you like
let temp = "fun1";
operations[temp]("Hello World");

It will also work with imported functions:

// mode.js
export function fun1(arg) {
  console.log(arg);
}

export function fun2(arg) {
  console.log(arg);
}

// index.js
import { fun1, fun2 } from "./mod";

const operations = {
  fun1,
  fun2
};

operations["fun1"]("Hello World");
operations["fun2"]("Hello World");

Since it is using property access, it will survive minimization or obfuscation, contrary to some answers you will find here.

Answer 16

Surprised to see no mention of setTimeout.

To run a function without arguments:

var functionWithoutArguments = function(){
    console.log("Executing functionWithoutArguments");
}
setTimeout("functionWithoutArguments()", 0);

To run function with arguments:

var functionWithArguments = function(arg1, arg2) {
    console.log("Executing functionWithArguments", arg1, arg2);
}
setTimeout("functionWithArguments(10, 20)");

To run deeply namespaced function:

var _very = {
    _deeply: {
        _defined: {
            _function: function(num1, num2) {
                console.log("Execution _very _deeply _defined _function : ", num1, num2);
            }
        }
    }
}
setTimeout("_very._deeply._defined._function(40,50)", 0);

Answer 17

So, like others said, definitely the best option is:

window['myfunction'](arguments)

And like Jason Bunting said, it won't work if the name of your function includes an object:

window['myobject.myfunction'](arguments); // won't work
window['myobject']['myfunction'](arguments); // will work

So here's my version of a function that will execute all functions by name (including an object or not):

my = {
    code : {
        is : {
            nice : function(a, b){ alert(a + "," + b); }
        }
    }
};

guy = function(){ alert('awesome'); }

function executeFunctionByName(str, args)
{
    var arr = str.split('.');
    var fn = window[ arr[0] ];
    
    for (var i = 1; i < arr.length; i++)
    { fn = fn[ arr[i] ]; }
    fn.apply(window, args);
}

executeFunctionByName('my.code.is.nice', ['arg1', 'arg2']);
executeFunctionByName('guy');

Answer 18

  let t0 = () => { alert('red0') }
  var t1 = () =>{ alert('red1') }
  var t2 = () =>{ alert('red2') }
  var t3 = () =>{ alert('red3') }
  var t4 = () =>{ alert('red4') }
  var t5 = () =>{ alert('red5') }
  var t6 = () =>{ alert('red6') }

  function getSelection(type) {
    var evalSelection = {
      'title0': t0,
      'title1': t1,
      'title2': t2,
      'title3': t3,
      'title4': t4,
      'title5': t5,
      'title6': t6,
      'default': function() {
        return 'Default';
      }
    };
    return (evalSelection[type] || evalSelection['default'])();
  }
  getSelection('title1');

A more OOP solution ...

Answer 19

One more detail on Jason and Alex's posts. I found it helpful to add a default value to context. Just put context = context == undefined? window:context; at the beginning of the function. You can change window to whatever your preferred context is, and then you won't need to pass in the same variable each time you call this in your default context.

Answer 20

To add to Jason Bunting's answer, if you're using nodejs or something (and this works in dom js, too), you could use this instead of window (and remember: eval is evil:

this['fun'+'ctionName']();

Answer 21

There's a very similar thing in my code. I have a server-generated string which contains a function name which I need to pass as a callback for a 3rd party library. So I have a code that takes the string and returns a "pointer" to the function, or null if it isn't found.

My solution was very similar to "Jason Bunting's very helpful function" *, although it doesn't auto-execute, and the context is always on the window. But this can be easily modified.

Hopefully this will be helpful to someone.

/**
 * Converts a string containing a function or object method name to a function pointer.
 * @param  string   func
 * @return function
 */
function getFuncFromString(func) {
    // if already a function, return
    if (typeof func === 'function') return func;

    // if string, try to find function or method of object (of "obj.func" format)
    if (typeof func === 'string') {
        if (!func.length) return null;
        var target = window;
        var func = func.split('.');
        while (func.length) {
            var ns = func.shift();
            if (typeof target[ns] === 'undefined') return null;
            target = target[ns];
        }
        if (typeof target === 'function') return target;
    }

    // return null if could not parse
    return null;
}

Answer 22

Here's a bit robust and reusable solution I ended up implementing for one of my projects.

A FunctionExecutor Constructor Function

Usage:

let executor = new FunctionExecutor();
executor.addFunction(two)
executor.addFunction(three)

executor.execute("one");
executor.execute("three");

Obviously in the project the adding of all the functions that required to be called by name was done by a loop.

The function Executor:

function FunctionExecutor() {
  this.functions = {};

  this.addFunction = function (fn) {
    let fnName = fn.name;
    this.functions[fnName] = fn;
  }

  this.execute = function execute(fnName, ...args) {
    if (fnName in this.functions && typeof this.functions[fnName] === "function") {
      return this.functions[fnName](...args);
    }
    else {
      console.log("could not find " + fnName + " function");
    }
  }

  this.logFunctions = function () {
    console.log(this.functions);
  }
}

Example Usage:

function two() {
  console.log("two"); 
}

function three() {
  console.log("three");
}

let executor = new FunctionExecutor();
executor.addFunction(two)
executor.addFunction(three)

executor.execute("one");
executor.execute("three");

Answer 23

  const myFnCollection = {
    myFnStringName: function(args) {}
  };

  let fn = 'myFnStringName';

  // 1. Recommended
  if (typeof window[fn] === 'function') {
    window[fn](args);
  }

  // 2. Recommended
  if (typeof myFnCollection[fn] === 'function') {
    myFnCollection[fn](args);
  }

  // 3. Eval is evil ;)
  if (typeof eval(fn) === 'function') {
    eval(fn)(args);
  }

Answer 24

There too some very helpful way.

http://devlicio.us/blogs/sergio_pereira/archive/2009/02/09/javascript-5-ways-to-call-a-function.aspx

var arrayMaker = {  
    someProperty: 'some value here',  
    make: function (arg1, arg2) {  
        return [ this, arg1, arg2 ];  
    },
    execute: function_name
};

Answer 25

I can't resist mentioning another trick, which helps if you have an unknown number of arguments that are also being passed as part of the string containing the function name. For example:

var annoyingstring = 'call_my_func(123, true, "blah")';

If your Javascript is running on a HTML page, all you need is an invisible link; you can pass a string into the onclick attribute, and the call the click method.

<a href="#" id="link_secret"><!-- invisible --></a>

$('#link_secret').attr('onclick', annoyingstring);
$('#link_secret').click();

Or create the <a> element at runtime.

Answer 26

Easiest way is to access it like has element

window.ClientSideValidations.forms.location_form

is same as

window.ClientSideValidations.forms['location_form']

Answer 27

People keep saying that eval is dangerous and evil because it can run any arbitrary code. However, if you use eval with a whitelisting approach, assuming you know all the possible function names that may need to be run in advance, then eval is no longer a security concern because the input is no longer arbitrary. Whitelisting is a good and frequent security pattern. Here's an example:

function runDynamicFn(fnName, ...args) {
  // can also be fed from a tightly controlled config
  const allowedFnNames = ['fn1', 'ns1.ns2.fn3', 'ns4.fn4'];

  return allowedFnNames.includes(fnName) ? eval(fnName)(...args) : undefined; 
}

// test function:
function fn1(a) { 
  console.log('fn1 called with', a)
}

runDynamicFn('alert("got you!")')
runDynamicFn('fn1', 'foo')

Answer 28

I like concise solutions, so come up with this more ES6 way:

const executeByName = (name, originContext, ...args) => {
  const namespaces = name.split('.');
  const func = namespaces.pop();
  const funcContext = namespaces.reduce((context, namespace) => context[namespace], originContext);
  return funcContext[func](...args);
};

Answer 29

This is working for me:

var command = "Add";
var tempFunction = new Function("Arg1","Arg2", "window." + command + "(Arg1,Arg2)");
tempFunction(x,y);

I hope this works.

Answer 30

Look basic:

var namefunction = 'jspure'; // String

function jspure(msg1 = '', msg2 = '') { 
  console.log(msg1+(msg2!=''?'/'+msg2:''));
} // multiple argument

// Results ur test
window[namefunction]('hello','hello again'); // something...
eval[namefunction] = 'hello'; // use string or something, but its eval just one argument and not exist multiple

Exist other type function is class and look example nils petersohn

Answer 31

Thanks for the very helpful answer. I'm using Jason Bunting's function in my projects.

I extended it to use it with an optional timeout, because the normal way to set a timeout wont work. See abhishekisnot's question

function executeFunctionByName(functionName, context, timeout /*, args */ ) {
 var args = Array.prototype.slice.call(arguments, 3);
 var namespaces = functionName.split(".");
 var func = namespaces.pop();
 for (var i = 0; i < namespaces.length; i++) {
  context = context[namespaces[i]];
 }
 var timeoutID = setTimeout(
  function(){ context[func].apply(context, args)},
  timeout
 );
    return timeoutID;
}

var _very = {
    _deeply: {
        _defined: {
            _function: function(num1, num2) {
                console.log("Execution _very _deeply _defined _function : ", num1, num2);
            }
        }
    }
}

console.log('now wait')
executeFunctionByName("_very._deeply._defined._function", window, 2000, 40, 50 );

Answer 32

There are several executeByName functions here which works fine, unless name contains square brackets - issue I ran into - as I have dynamically generated names. So above functions will fail on names like

app.widget['872LfCHc']['toggleFolders']

As a remedy, I've made function to take this into account too, maybe someone will find it usefull:

Generated from CoffeeScript:

var executeByName = function(name, context) {
  var args, func, i, j, k, len, len1, n, normalizedName, ns;
  if (context == null) {
    context = window;
  }
  args = Array.prototype.slice.call(arguments, 2);
  normalizedName = name.replace(/[\]'"]/g, '').replace(/\[/g, '.');
  ns = normalizedName.split(".");
  func = context;
  for (i = j = 0, len = ns.length; j < len; i = ++j) {
    n = ns[i];
    func = func[n];
  }
  ns.pop();
  for (i = k = 0, len1 = ns.length; k < len1; i = ++k) {
    n = ns[i];
    context = context[n];
  }
  if (typeof func !== 'function') {
    throw new TypeError('Cannot execute function ' + name);
  }
  return func.apply(context, args);
}

For better readability check also CoffeeScript version:

executeByName = (name, context = window) ->
    args = Array.prototype.slice.call(arguments, 2)
    normalizedName = name.replace(/[\]'"]/g, '').replace(/\[/g, '.')
    ns = normalizedName.split "."
    func = context
    for n, i in ns
        func = func[n]

    ns.pop()
    for n, i in ns
        context = context[n];
    if typeof func != 'function'
        throw new TypeError 'Cannot execute function ' + name
    func.apply(context, args)

Answer 33

You can call javascript function within the eval("functionname as string") either. Like below: (eval is pure javascript function)

function testfunc(){
    return "hello world";
}

$( document ).ready(function() {

     $("div").html(eval("testfunc"));
});

Working example: https://jsfiddle.net/suatatan/24ms0fna/4/

Answer 34

all you have to do is use a context or define a new context where your function(s) reside. you are not limited to window["f"]();

here is an example of how I use some dynamic invocation for some REST services.

/* 
Author: Hugo Reyes
@ www.teamsrunner.com

*/

    (function ( W, D) { // enclose it as a self-invoking function to avoid name collisions.


    // to call function1 as string
    // initialize your FunctionHUB as your namespace - context
    // you can use W["functionX"](), if you want to call a function at the window scope.
    var container = new FunctionHUB();


    // call a function1 by name with one parameter.
    
    container["function1"](' Hugo ');


    // call a function2 by name.
    container["function2"](' Hugo Leon');
    

    // OO style class
    function FunctionHUB() {

        this.function1 = function (name) {

            console.log('Hi ' + name + ' inside function 1')
        }

        this.function2 = function (name) {

            console.log('Hi' + name + ' inside function 2 ')
        }
    }

})(window, document); // in case you need window context inside your namespace.

If you want to generate the entire function from a string, that's a different answer. also please notice that you are not limited to a single namespace, if your namespace exists as my.name.space.for.functions.etc.etc.etc the last branch of your namespace contains the function as my.name.space.for.functions.etc.etc["function"]();

Hope it helps. H.

Answer 35

Since eval() is evil, and new Function() is not the most efficient way to achieve this, here is a quick JS function that returns the function from its name in string.

• Works for namespace'd functions
• Fallbacks to null-function in case of null/undefined string
• Fallbacks to null-function if function not found

    function convertStringtoFunction(functionName){

        var nullFunc = function(){}; // Fallback Null-Function
        var ret = window; // Top level namespace

        // If null/undefined string, then return a Null-Function
        if(functionName==null) return nullFunc;

        // Convert string to function name
        functionName.split('.').forEach(function(key){ ret = ret[key]; });

        // If function name is not available, then return a Null-Function else the actual function
        return (ret==null ? nullFunc : ret);

    }

Usage:

    convertStringtoFunction("level1.midLevel.myFunction")(arg1, arg2, ...);

Answer 36

You may place your functions names in an Array object and then call the array key respective to each function to execute it, DEMO:

function captchaTest(msg){
    let x = Math.floor(Math.random()*(21-1)) +1;
    let y = Math.floor(Math.random()*(11-1)) +1;
    let sum = function(){
        return x+y;
    }
    let sub = function(){
        if (y > x){
            let m = y;
            y = x;
            x = m;
            console.log(x,y,m,'--')
        }
        return x-y;
    }
    let mul = function(){
        return x*y;
    } 
    let OParr = [sum(), sub(), mul()]; 
    let OP = Math.floor(Math.random()*OParr.length);      
    let s = OParr[OP]; //!!! HERE !!! is the call as array element
    switch(OP){
        case 0:
            opra = '＋';
            break;
        case 1:
            opra = '━';
            break;
        default:
            opra = '✖';
    }
    let msg2 = 'Answer the following question to continue:'
    let p = prompt(msg+' '+msg2+'\n'+'What is the result of '+x+opra+y+' ?','')
    console.log(s,p,OP)
    if (s == p){
        alert ('Wow, Correct Answer!')
        return true;
    }
    else{
        alert('Sorry, the answer is not correct!')
        return false;
    }
}

Answer 37

Without using eval('function()') you could to create a new function using new Function(strName). The below code was tested using FF, Chrome, IE.

<html>
<body>
<button onclick="test()">Try it</button>
</body>
</html>
<script type="text/javascript">

  function test() {
    try {    
        var fnName = "myFunction()";
        var fn = new Function(fnName);
        fn();
      } catch (err) {
        console.log("error:"+err.message);
      }
  }

  function myFunction() {
    console.log('Executing myFunction()');
  }

</script>