Develop Reference

Add Argument to JS Promise

How can I alter the code I have to accomplish to goal of referencing the original event (or properties/methods of it) in the subsequent code.
tViz.addEventListener(tableauSoftware.TableauEventName.MARKS_SELECTION, onMarksSelection);
function onMarksSelection(marksEvent) {
return marksEvent.getMarksAsync().then(showMarksHelp);
}
function showMarksHelp(marks){
I want to access a method from the marksEvent variable but here I can only access
the marks variable from getMarksAsync(). I need it here because stuff will also be
based on the marks variable contained here.
}
I feel like I could restructure my JS to accomplish this or pass something in somewhere, but after reading about Promises and the Tableau documentation I'm still lost. I don't want to use any global variables.
EDIT
So I changed my code to the below:
function onMarksSelection(marksEvent) {
var marks = marksEvent.getMarksAsync().then(function(marks){
showMarksHelp(marks,marksEvent)
});
}
function showMarksHelp(marks,marksEvent){}
Is this a/the correct method to accomplish what I did? I just made it up but it seems like it works.

Using an anonymous function, you can capture the value of marksEvent and then call showMarksHelp with two arguments.
function onMarksSelection(marksEvent) {
return marksEvent.getMarksAsync().then(function(marks) {
// marksEvent is accessible in here
showMarksHelp(marksEvent, marks);
});
}
function showMarksHelp(marksEvent, marks) {
// content of showMarksHelp here
}

call a js function based on the argument passed

I'm trying to call a js function within another one, but use the argument to specify the function. ie depending on the argument passed, it will call a different function
function toggle(n){
if (sessionStorage['toggle'+n]== 0){
check+n();
}
else
}
So, for example, if the argument 'Balloons' was passed as n, then it will call the function checkBalloons(). "check+n();" is not currently working here. Sorry for my lack of simple js syntax!

If the function is defined in the global scope (browser) you can do:
window["check"+n]();
or some tenants like Node.js you would access it from global object.
global["check"+n]();
if it is a part of some other object then you would do the same.
obj["check"+n]();
Functions and properties defined on an object can be accessed using [] convention as well. i.e obj["propFuncName"] will give you reference to it, so in case of methods you add () to invoke it.

If the function is global, you would do this:
window["check" + n]();
or, you could put your function in an object like so:
myNamespace = {};
myNamespace.checkSomething = function(){ /* ... */ }
// call it like this:
myNamespace["check" + n]();

The answers thus far are correct, but lack explanation.
In JavaScript, you cannot call a function by name when that name is a string. What you can do is retrieve a value from an object by name, and if that value happens to be a function, you can then call it. For example:
var myObject = {};
myObject.myFunction = function() { alert('test!'); };
// Get the property on `myObject` called `myFunction`
var theFunctionLookup = myObject['myFunction'];
// Since that property was a function, you can call it!
theFunctionLookup();
In the browser, functions that are defined in the global scope are attached to the window object. For example, this works:
function myFunction() { alert('test'); }
var theFunctionLookup = window['myFunction'];
theFunctionLookup();
You can shorten the last two lines into one:
function myFunction() { alert('test'); }
// Look up and call the function in one line.
window['myFunction']();
For the same reasons, you can use a dynamically-calculated string to look up functions.
function checkBalloon() {
alert('checking balloon');
}
function toggle(n){
if (sessionStorage['toggle'+n]== 0){
window['check' + n]();
check+n();
}
}
toggle('Balloon');

if you do this way:
if (sessionStorage['toggle'+n]== 0){
window["check" + n]();
}
will work

How do I make a nonexistent (non-member, non-global) method invocable without using eval?

Let's start from the code:
function say(name) {
var ghost=function () {
function ghost() {
alert('!');
};
return body;
};
eval("var body=''+"+name+';');
eval(name+('=('+ghost).replace('body', body)+')();');
eval(name+'();');
}
function Baal() {
if ('undefined'===typeof ghost) {
say('Baal');
return;
}
ghost();
}
say('Baal'); // or just Baal();
Looks like that saying the devil's name invoke his presence (well, maybe he needs somebody for spiritual possession) ..
As you can see the ghost doesn't exist along with Baal, but we can invoke it since there're evals in say(name).
say(name) reassigns Baal to its code body as a closure and makes it captured a ghost method, that's how things work. But I'm trying to avoid eval ..
So .. let me reword the question:
How do I make a nonexistent(and not a member or global) method invocable without using eval?

Let me rephrase your question, just to make sure I’ve got it. Given a function, you want to put a new variable in its scope, without that scope being the global scope or a scope shared between the caller and the subject, without using eval (or the equivalent new Function and other hacks depending on the environment).
You can’t.
In the case you just mentioned, you could define one function, base(), that uses arguments.callee.caller.
Don’t do that.

The short answer: You don't.
That scope is not available. If you were to attach the scope then it would be available inside of the scope used. You could then access the method handles. I assume this is not what you were looking for, but here is what that would look like. demo
function say(name){
var methods = {};
methods.Baal = function(){
alert("!");
};
return methods[name];//this could invoke as well: methods[name]()
}
var handle = say('Baal');
handle();
What your evals break down to is something along these lines (although with dynamic content from string building - this is the end result)
function say(name) {
var Baal = (function () {
function ghost() {
alert('!');
};
return function(){
if ('undefined'===typeof ghost) {
say('Baal');
return;
}
ghost();
}
})();
Baal();
}
say('Baal'); // or just Baal();
Note that the meat of what happens here is from the function Baal, namely that it calls a hardcoded ghost() which in turn calls a hardcoded alert. Why go through all of this trouble to access a hardcoded function?
A better way would be to inject this function as a callback which expects some parameters to be injected.
jsFiddle Demo
function say(callback){
var params = "!";
if( typeof callback == "function" ){
callback(params);
}
}
say(function(params){
alert(params);
});

It's very difficult for me to read through your code and figure out what you are trying to accomplish with it, but it appears that you are trying to introduce a variable into the current scope so that you can call it. You cannot do this in javascript with the method that you demonstrated. Scoping only ever "flows down". By that I mean that a variable or function defined within a function will only be available to that function and any other functions defined therein. Your function named ghost will only ever be available within the function where it is defined, regardless of when that function is evaluated.
What you can do, however, is write a function that returns a function. You can then call that function and assign the result to a variable in the scope where you want to expose functionality. Doing that would look something like this.
function defineSpecialAlert() {
return function(name) {
alert(name + "!");
};
}
var newlyDefinedMethod = defineSpecialAlert();
newlyDefinedMethod("Baal");

So if I understand, it seems like you want to create an alias of eval: Something like
#Note this code is not intended as a solution, but demonstrates
#an attempt that is guaranteed to fail.
#
function myAlias(ctx) {
eval.call(ctx, 'var ghost = 42');
}
myAlias(this);
alert(ghost);
Javascript allows many funky sleight-of-hand tricks especially with closures, but this is maybe the one impossible thing that javascript cannot do. I've tried at length to do this exact same thing, and I can tell you that you'll run into nothing but complaints from the browser, saying that eval cannot be re-contexted or aliased in any way.

Javascript: Possible to pass function commands to another function via a variable?

Ok hopefully this come across correctly. I am building a universal javascript function that will build a menu and then also build the functions that each menu item would call. To do this, I need to pass a list of the commands to be called for each option.
So for example:
var thecall = 'alert("hi, this works");';
function myfunction(thecall)
{
//In here I want to excute whatever commands is listed in variable thecall
.....
}
I'm sure doing it this way is completely stupid, but I don't know how else to do this.
Basically, I need my function to perform other functions on a variable basis.
Thanks!!

I made it a bit fancier to show you how you can use it.
var thecall = function(name){alert("hi " + name + ", this works");};
function myFunction(function_ref)
{
function_ref('Mark');
}
myFunction(thecall);

You can execute arbitrary strings of JavaScript using eval(), but that is not the best solution for you here (it's almost never the best solution).
Functions in JavaScript are themselves objects which means you can store multiple references to the same function in multiple variables, or pass function references as parameters, etc. So:
var thecall = function() {
alert("hi, this works");
};
function myfunction(someFunc) {
someFunc(); // call the function that was passed
}
myfunction(thecall); // pass reference to thecall
Note that when passing the reference to the thecall function there are no parentheses, i.e., you say thecall not thecall(): if you said myfunction(thecall()) that would immediately call thecall and pass whatever it returned to myfunction. Without the parentheses it passes a reference to thecall that can then be executed from within myfunction.
In your case where you are talking about a list of menu items where each item should call a particular function you can do something like this:
var menuItems = [];
function addMenuItem(menuText, menuFunction) {
menuItems.push({ "menuText" : menuText, "menuFunction" : menuFunction });
}
function test1() {
// do something
}
addMenuItem("Test 1", test1);
addMenuItem("Test 2", function() { alert("Menu 2"); });
// and to actually call the function associated with a menu item:
menuItems[1].menuFunction();
Notice the second menu item I'm adding has an anonymous function defined right at the point where it is passed as a parameter to addMenuItem().
(Obviously this is an oversimplified example, but I hope you can see how it would work for your real requirement.)

I think your looking for the eval function.
var code= 'alert("hi, this works");';
eval(code);

jQuery Function Implementation and Function Call?

What is the difference of calling function like:
testCall: function() and function testCall() in jQuery ?
Update:
Questions: Does usage of one over the another have some performance issues related to it OR it really does not matter which one you are using ?
Update 2
Also other thing that I noticed that whenn I am defining function using testCall: function() and I call it using this.testCall() it works fine and am able to call it in any other function.
But when I am using function testCall() and I try to call it using testCall() in another function than I am getting errors and am not able to call it. Is this possible or there could be some other reason for the errors ?

In this example:
testCall: function()
testCall is now a function available on the object you're in, like this: object.testCall() It can access other functions, properties, etc inside this object if it needs to.
In this version:
function testCall()
testCall is just a globally available method, not scoped to the object or plugin, whatever you're dealing with, you can call it from anywhere, like this: testCall()

This is really a question about Javascript syntax (and semantics), not jQuery.
Both of those constructions define functions. This:
var x = {
// ...
name: function() { /* ... */ },
// ...
};
defines a function (an anonymous function) and assigns it as the value of the property called "name" in the object being assigned to the variable "x".
This:
function name() {
/* ... */
}
defines a function with the name "name". The effect is similar to:
var name = function() { /* ... */ };
but definitely different. However, for most purposes it's safe to think about them as being almost the same. The effect is that "name" is bound to the function in the lexically-enclosing scope. If you do that definition outside of any other function, then "name" becomes a property of the "window" object, and the function is therefore globally available. If that declaration is inside another function, then "name" is only available inside that function.
Usually you see the first form when you're doing something like setting up callbacks for some jQuery facility, like a UI plugin or $.ajax. You're giving jQuery a function that it should call upon something happening — an AJAX call finishing, or a use action like a mouse click, or completion of some sort of animation.
edit oh, and finally here's another note. If you define a function the second way, well then you can refer to that function by name and use it in an object definition (like the first example):
function globalFunction() {
function localFunction() { /* ... */ };
jQuery.something({
x: 100, y: 100,
callback: localFunction,
// ...
});
}
Many more such things are possible - functions are values in Javascript and can be tossed around as easily as numbers and strings.

The first (testCall: function()) is object literal notation for defining a function and assigning it to a property on an object (not shown). The function itself is anonymous; the property it is bound to has a name, but the function does not.
The second (function testCall()) is a named function.
Named functions have several advantages over anonymous ones, and so though you see the first format quite a lot, I would recommend using it sparingly if at all. Named functions can be reported usefully by your tools (debuggers and the like), whereas anonymous functions just show up as ? or (anonymous). More here.
For that reason, rather than this:
function doSomeNiftyAjaxyThing(foo) {
$.ajax({
url: "blah",
success: function() {
// Do something involving the successful result and `foo`
foo.bar();
}
});
}
I would typically do this instead:
function doSomeNiftyAjaxyThing(foo) {
$.ajax({
url: "blah",
success: niftySuccess
});
function niftySuccess() {
// Do something involving the successful result and `foo`
foo.bar();
}
}
Not only does this keep my code a bit cleaner (er, to my mind), but it means that if something goes wrong inside niftySuccess, I've given the function a name my tools can report to me. Note that other than the fact that the function has a name, they're identical – both functions are closures over the foo argument and anything else inside doSomeNiftyAjaxyThing.
You might be tempted to give the function a name inline, like so:
function doSomeNiftyAjaxyThing(foo) {
$.ajax({
url: "blah",
success: function niftySuccess() { // <== change here, PROBLEMATIC
// Do something involving the successful result and `foo`
foo.bar();
}
});
}
There you're declaring a function with a name as an expression, and assigning the result of the expression to a property. Arguably you should be able to do that, but there are a series of implementation...anomalies in the various Javascript engines out there that prevent your being able to do that. (More in the article linked above, and in this article.)