Get return value after SetTimeout

Question

I've just asked about calling functions by name, now I want to process return statement after SetTimeout:

function ECall(funcName, arg)
{
    command += "(";
    for (var i=1; i<arguments.length; i++) 
    {
        command += "'" + arguments[i] + "'";
        if (i != arguments.length-1) command += ',';
    }
    command += ")";

    //var funcPtr = eval(funcName);
    //return funcPtr(arg); // This works, but I need SetTimeout

    setTimeout('window[\'' + funcName + '\']' + command, 1000);
}

setTimeout works great, but I have to save return value of called function. When I write: setTimeout('alert(window[\'' + funcName + '\']' + command + ')', 1000); It alerts return value of function. How can I store it?

Answer 1

You don't need to use any of this string manipulation. Just pass a function reference to window.setTimeout(). To store the returned value of the function, simply assign it to a variable in the function you pass to window.setTimeout()

var savedValue;

function ECall(funcName)
{
    var args = Array.prototype.slice.call(arguments, 1);
    var func = window[funcName];

    window.setTimeout(function() {
        savedValue = func.apply(this, args);
    }, 1000);
}

Answer 2

If you wanted to return a value from ECall, it won't work.

The setTimeout is asynchronous, which means that the ECall will return before the setTimeout code is invoked.

Or if you wanted the alert() to be part of the setTimeout, you could pass an anonymous function. Also, it would be better to not pass a string to the setTimeout.

I'd do this instead:

function ECall(funcName, arg)
{
       // Get an Array of the arguments, except for the first one.
    var args = Array.prototype.slice.call( arguments, 1 );

       // Pass an anonymous function that calls the global "funcName" function
       //    inside the alert(). 
       // It uses .apply() to pass the arguments we sliced.
    setTimeout( function() {
        alert( window[ funcName ].apply( window, args ) );
    }, 1000);
}