How to turn a String into a JavaScript function call? [duplicate]

Answer 1

This took me a while to figure out, as the conventional window['someFunctionName']() did not work for me at first. The names of my functions were being pulled as an AJAX response from a database. Also, for whatever reason, my functions were declared outside of the scope of the window, so in order to fix this I had to rewrite the functions I was calling from

function someFunctionName() {}

to

window.someFunctionName = function() {}

and from there I could call window['someFunctionName']() with ease. I hope this helps someone!

Answer 2

In javascript that uses the CommonJS spec, like node.js for instance you can do what I show below. Which is pretty handy for accessing a variable by a string even if its not defined on the window object. If there is a class named MyClass, defined within a CommonJS module named MyClass.js

// MyClass.js
var MyClass = function() {
    // I do stuff in here. Probably return an object
    return {
       foo: "bar"
    }
}

module.exports = MyClass;

You can then do this nice bit o witchcraft from another file called MyOtherFile.js

// MyOtherFile.js

var myString = "MyClass";

var MyClass = require('./' + myString);
var obj = new MyClass();

console.log(obj.foo); // returns "bar"

One more reason why CommonJS is such a pleasure.

Answer 3

Here is a more generic way to do the same, while supporting scopes :

// Get function from string, with or without scopes (by Nicolas Gauthier)
window.getFunctionFromString = function(string)
{
    var scope = window;
    var scopeSplit = string.split('.');
    for (i = 0; i < scopeSplit.length - 1; i++)
    {
        scope = scope[scopeSplit[i]];

        if (scope == undefined) return;
    }

    return scope[scopeSplit[scopeSplit.length - 1]];
}

Hope it can help some people out.

Answer 4

While I like the first answer and I hate eval, I'd like to add that there's another way (similar to eval) so if you can go around it and not use it, you better do. But in some cases you may want to call some javascript code before or after some ajax call and if you have this code in a custom attribute instead of ajax you could use this:

    var executeBefore = $(el).attr("data-execute-before-ajax");
    if (executeBefore != "") {
        var fn = new Function(executeBefore);
        fn();
    }

Or eventually store this in a function cache if you may need to call it multiple times.

Again - don't use eval or this method if you have another way to do that.

Answer 5

I wanted to be able to take a function name as a string, call it, AND pass an argument to the function. I couldn't get the selected answer for this question to do that, but this answer explained it exactly, and here is a short demo.

function test_function(argument)    {
    alert('This function ' + argument); 
}

functionName = 'test_function';

window[functionName]('works!');

This also works with multiple arguments.

Answer 6

Based on Nicolas Gauthier answer:

var strng = 'someobj.someCallback';
var data = 'someData';

var func = window;
var funcSplit = strng.split('.');
for(i = 0;i < funcSplit.length;i++){
   //We maybe can check typeof and break the bucle if typeof != function
   func = func[funcSplit[i]];
}
func(data);