JavaScript: invoke function or call a property via reflection - Stack Overflow

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Is there a way to call a function (or a property) on an object via reflection, in JavaScript?

Lets say that during run-time, my code has already determined that objectFoo indeed has a property called 'bar'. Now that my code knows that, the next thing I want to do is invoke that. Normally i would do this: var x = objectFoo.bar. But 'bar' was determined at run time, so I need to invoke it using reflection.

Is there a way to call a function (or a property) on an object via reflection, in JavaScript?

Lets say that during run-time, my code has already determined that objectFoo indeed has a property called 'bar'. Now that my code knows that, the next thing I want to do is invoke that. Normally i would do this: var x = objectFoo.bar. But 'bar' was determined at run time, so I need to invoke it using reflection.

• javascript
• reflection

Share Improve this question Follow edited Dec 22, 2009 at 19:15 7wp asked Dec 22, 2009 at 19:09 7wp7wp 12.7k2020 gold badges7878 silver badges107107 bronze badges

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4 Answers 4

Sorted by: Reset to default 7

In JavaScript, object methods are really just properties containing functions. Like all properties, you can refer to them using associative array syntax:

var x = { 'a': 1 };
x.a += 1;
x['a'] += 1;
console.log(x.a);

Output is: 3.

So if you have the name of a method you want to invoke on myObject:

var methodName = 'myMethod';

// Invoke the value of the 'myMethod' property of myObject as a function.
myObject[methodName]();

EVAL: http://www.w3schools.com/jsref/jsref_eval.asp

Eval will allow you to run any javascript code by passing in a string and having the javascript engine evaluate it as javascript code.

If you mean that you want to first search a list properties of an object, then look at this:

var o = {}
for(att in o){
    alert(o[att]);
}

If you do this, you can even set the property's value by accessing it as if it were an array (all objects are actually associative arrays).

obj["propertyName"] = "new value";
obj["MethodName"]();

Create object (invoke constructor) via reflection:

SomeClass = function(arg1, arg2) {
    console.log('Your reflection');
}

ReflectUtil.newInstance('SomeClass', 5, 7);

and implementation:

var ReflectUtil = {};

/**
 * @param strClass:
 *          class name
 * @param optionals:
 *          constructor arguments
 */
ReflectUtil.newInstance = function(strClass) {
    var args = Array.prototype.slice.call(arguments, 1);
    var clsClass = eval(strClass);
    function F() {
        return clsClass.apply(this, args);
    }
    F.prototype = clsClass.prototype;
    return new F();
};

Create a register object:

var funcRegister = {};

Create a function to call the other:

var callReflectionFunc = function(type, obj) {
    var func = false;
    if(funcRegister[type])
        func = funcRegister[type](obj);

    return func;
}

Populate your register with functions:

funcRegister['yourtype1'] = function(obj) {
    console.log('your type 2');

    return obj;
}

funcRegister['yourtype2'] = function(obj) {
    console.log('your type 2');

    return obj;
}

Then call it with your type and an object where you can put your args

callReflectionFunc(type, obj);

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