How to avoid JavaScript eval() for a method call by name?

Question

I have a JavaScript code where I need to call a method by its name. The method name is generated during run-time.

I use the following code to extract the method name and call the method with the JavaScript method eval():

// e.g. modelField='getData()';
if (modelField.match("^[_a-zA-Z0-9.]+\\(")) {
    try {
        // test if method is defined by the model object...
        methodName=modelField.substring(0,modelField.indexOf('('));
        if ($.isFunction(model[methodName])) {
            modelValue = eval('model.' + modelField);
        } 
    } catch (err) {
        console.error("Error calling gettermethod '"
                + modelField + "' -> " + err.message);
    }
}

Is it possible to avoid the eval() call here?

Solution:

Finally I found the following solution for my problem. The method accepts parameters and is used only is a specific context which need to be provided by the caller:

/*
 * helper method to call a model getter/setter method by name. The method
 * expects theh funtion name including the parameters
 * 
 * e.g. setValue('abc');
 * 
 * Optional additional params can be set which will be added to the function
 * call
 */
_executeFunctionByName = function(functionCall, context, params) {
    var paramPos,methodName,args,fnparams,fn;
    
    paramPos = functionCall.indexOf('(');
    methodName = functionCall.substring(0, paramPos);
    args = functionCall.substring(paramPos + 1).trim();
    args = args.substring(0, args.indexOf(')')).trim();
    // first split the params...
    fnparams = args.split(",");
    if (params) {
        fnparams.push(params);
    }
    // clean param value ....
    $.each(fnparams, function(index, _obj) {
        // string literal ?
        if (_obj.indexOf("'") === 0 || _obj.indexOf('"') === 0) {
            fnparams[index] = _obj.substring(1, _obj.length - 1);
        } else {
            // param is treated as string literal           
        }
    });

    // find object
    fn = context[methodName];
    // is valid function?
    if (typeof fn === "function") {
        return fn.apply(context, fnparams);
    }
}

@Pointy: yes it will. He's using the modelField variable in the eval which includes the parens. (That's not to say it isn't odd setting a variable with parens in the first place, just the method name would have been enough). — Daniel Flint
– Daniel Flint, Commented Oct 16, 2015 at 21:39
@DanielFlint ah, OK, so the parens are there in the variable. — Pointy
– Pointy, Commented Oct 16, 2015 at 21:40

Pointy · Accepted Answer · 2015-10-16 21:29:21Z

4

You definitely don't need eval():

    if ($.isFunction(model[methodName])) {
        modelValue = model[modelField]();
    }

The [ ] operator accesses properties via the value of the contained expression. The () operator (if you can call it that) causes the value retrieved to be called as a function (if it is a function).

answered Oct 16, 2015 at 21:29

Pointy

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8 Comments

NG. Over a year ago

does he want to call model[methodName] or model[modelField]? Former seems more accurate based on the if condition.

Stephan Bijzitter Over a year ago

no need for jQuery when you can use var method = model[methodName]; method.call && method();

dandavis Over a year ago

@StephanBijzitter: that might not work if methodName uses this, so either call it explicitly or keep the method attached to the object.

Pointy Over a year ago

@NG. I don't know; I would assume that if the code puts a value in a variable called "methodName" that that would be the name of the method :) I could be wrong of course. The point is that there's no need for eval().

Ralph Over a year ago

Thanks for your answer. But what if I need also to pass parameters by name: e.g. modelField="getData('firstname',42)"; how can I pass these params 'firstname' and 42?

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