Javascript create new object from class name in string

Question

I've got this little bit of non working code:

PackageLoader.prototype.activate = function(name) {
    this.activePackages.push(new name());
}

What I'd like this to do is to push a new instance to the activePackages array, if the name it gets is a string. How to achieve this?

Where is this function? You have to have a way of finding the thing you want to push first. Would you rather make sure you pass the right function instead of finding the function in this step? — ditoslav
– ditoslav, Commented Nov 7, 2014 at 20:51

Greg Burghardt · Accepted Answer · 2014-11-07 21:16:28Z

2

If name does not refer to a "class" in the global scope, you can safely use eval:

function toConstructor(className) {
    if (!/^[$_a-z][$_a-z0-9.]*$/i.test(className)) {
        throw new Error("Invalid class name: " + className);
    }

    try {
        return eval(className);
    }
    catch (error) {
        return null;
    }
}

And to use it:

var Foo = {
    Bar: {
        Baz: function() {}
    }
};

var Klass1 = toConstructor("XMLHttpRequest");

var xhr = new Klass1();
xhr.onreadystatechange = function() {};

var Klass2 = toConstructor("Foo.Bar.Baz");
var baz = new Klass2(3);
console.log(baz.x); // logs 3

var Klass3 = toConstructor("I.Do.Not.Exist");

console.log(Klass3); // logs NULL

answered Nov 7, 2014 at 21:16

Greg Burghardt

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Comments

epascarello · Accepted Answer · 2014-11-07 20:50:50Z

0

Use bracket notation if it is in global scope

this.activePackages.push(new window[name]());

answered Nov 7, 2014 at 20:50

epascarello

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