When creating a JavaScript function with multiple arguments, I am always confronted with this choice: pass a list of arguments vs. pass an options object.
For example I am writing a function to map a nodeList to an array:
function map(nodeList, callback, thisObject, fromIndex, toIndex){
...
}
I could instead use this:
function map(options){
...
}
where options is an object:
options={
nodeList:...,
callback:...,
thisObject:...,
fromIndex:...,
toIndex:...
}
Which one is the recommended way? Are there guidelines for when to use one vs. the other?
[Update] There seems to be a consensus in favor of the options object, so I'd like to add a comment: one reason why I was tempted to use the list of arguments in my case was to have a behavior consistent with the JavaScript built in array.map method.
Like many of the others, I often prefer passing an options object to a function instead of passing a long list of parameters, but it really depends on the exact context.
I use code readability as the litmus test.
For instance, if I have this function call:
checkStringLength(inputStr, 10);
I think that code is quite readable the way it is and passing individual parameters is just fine.
On the other hand, there are functions with calls like this:
initiateTransferProtocol("http", false, 150, 90, null, true, 18);
Completely unreadable unless you do some research. On the other hand, this code reads well:
initiateTransferProtocol({
"protocol": "http",
"sync": false,
"delayBetweenRetries": 150,
"randomVarianceBetweenRetries": 90,
"retryCallback": null,
"log": true,
"maxRetries": 18
});
It is more of an art than a science, but if I had to name rules of thumb:
Use an options parameter if:
You have more than four parameters
Any of the parameters are optional
You've ever had to look up the function to figure out what parameters it takes
If someone ever tries to strangle you while screaming "ARRRRRG!"
Multiple arguments are mostly for obligatory parameters. There's nothing wrong with them.
If you have optional parameters, it gets complicated. If one of them relies on the others, so that they have a certain order (e.g. the fourth one needs the third one), you still should use multiple arguments. Nearly all native EcmaScript and DOM-methods work like this. A good example is the open method of XMLHTTPrequests, where the last 3 arguments are optional - the rule is like "no password without a user" (see also MDN docs).
Option objects come in handy in two cases:
You've got so many parameters that it gets confusing: The "naming" will help you, you don't have to worry about the order of them (especially if they may change)
You've got optional parameters. The objects are very flexible, and without any ordering you just pass the things you need and nothing else (or undefineds).
In your case, I'd recommend map(nodeList, callback, options). nodelist and callback are required, the other three arguments come in only occasionally and have reasonable defaults.
Another example is JSON.stringify. You might want to use the space parameter without passing a replacer function - then you have to call …, null, 4). An arguments object might have been better, although its not really reasonable for only 2 parameters.
Using the 'options as an object' approach is going to be best. You don't have to worry about the order of the properties and there's more flexibility in what data gets passed (optional parameters for example)
Creating an object also means the options could be easily used on multiple functions:
options={
nodeList:...,
callback:...,
thisObject:...,
fromIndex:...,
toIndex:...
}
function1(options){
alert(options.nodeList);
}
function2(options){
alert(options.fromIndex);
}
It can be good to use both. If your function has one or two required parameters and a bunch of optional ones, make the first two parameters required and the third an optional options hash.
In your example, I'd do map(nodeList, callback, options). Nodelist and callback are required, it's fairly easy to tell what's happening just by reading a call to it, and it's like existing map functions. Any other options can be passed as an optional third parameter.
I may be a little late to the party with this response, but I was searching for other developers' opinions on this very topic and came across this thread.
I very much disagree with most of the responders, and side with the 'multiple arguments' approach. My main argument being that it discourages other anti-patterns like "mutating and returning the param object", or "passing the same param object on to other functions". I've worked in codebases which have extensively abused this anti-pattern, and debugging code which does this quickly becomes impossible. I think this is a very Javascript-specific rule of thumb, since Javascript is not strongly typed and allows for such arbitrarily structured objects.
My personal opinion is that developers should be explicit when calling functions, avoid passing around redundant data and avoid modify-by-reference. It's not that this patterns precludes writing concise, correct code. I just feel it makes it much easier for your project to fall into bad development practices.
Consider the following terrible code:
function main() {
const x = foo({
param1: "something",
param2: "something else",
param3: "more variables"
});
return x;
}
function foo(params) {
params.param1 = "Something new";
bar(params);
return params;
}
function bar(params) {
params.param2 = "Something else entirely";
const y = baz(params);
return params.param2;
}
function baz(params) {
params.params3 = "Changed my mind";
return params;
}
Not only does this kind of require more explicit documentation to specify intent, but it also leaves room for vague errors.
What if a developer modifies param1 in bar()? How long do you think it would take looking through a codebase of sufficident size to catch this?
Admittedly, this is example is slightly disingenuous because it assumes developers have already committed several anti-patterns by this point. But it shows how passing objects containing parameters allows greater room for error and ambiguity, requiring a greater degree of conscientiousness and observance of const correctness.
Just my two-cents on the issue!
Your comment on the question:
in my example the last three are optional.
So why not do this? (Note: This is fairly raw Javascript. Normally I'd use a default hash and update it with the options passed in by using Object.extend or JQuery.extend or similar..)
function map(nodeList, callback, options) {
options = options || {};
var thisObject = options.thisObject || {};
var fromIndex = options.fromIndex || 0;
var toIndex = options.toIndex || 0;
}
So, now since it's now much more obvious what's optional and what's not, all of these are valid uses of the function:
map(nodeList, callback);
map(nodeList, callback, {});
map(nodeList, callback, null);
map(nodeList, callback, {
thisObject: {some: 'object'},
});
map(nodeList, callback, {
toIndex: 100,
});
map(nodeList, callback, {
thisObject: {some: 'object'},
fromIndex: 0,
toIndex: 100,
});
It depends.
Based on my observation on those popular libraries design, here are the scenarios we should use option object:
The parameter list is long (>4).
Some or all parameters are optional and they don’t rely on a certain
order.
The parameter list might grow in future API update.
The API will be called from other code and the API name is not clear
enough to tell the parameters’ meaning. So it might need strong
parameter name for readability.
And scenarios to use parameter list:
Parameter list is short (<= 4).
Most of or all of the parameters are required.
Optional parameters are in a certain order. (i.e.: $.get )
Easy to tell the parameters meaning by API name.
Object is more preferable, because if you pass an object its easy to extend number of properties in that objects and you don't have to watch for order in which your arguments has been passed.
For a function that usually uses some predefined arguments you would better use option object. The opposite example will be something like a function that is getting infinite number of arguments like: setCSS({height:100},{width:200},{background:"#000"}).
I would look at large javascript projects.
Things like google map you will frequently see that instantiated objects require an object but functions require parameters. I would think this has to do with OPTION argumemnts.
If you need default arguments or optional arguments an object would probably be better because it is more flexible. But if you don't normal functional arguments are more explicit.
Javascript has an arguments object too.
https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Functions_and_function_scope/arguments
I am using James Montemagno's Xamarin Media Plugin (https://github.com/jamesmontemagno/MediaPlugin) and his usage example shows an image being updated in this way from the captured photo:
targetImage.Source = ImageSource.FromStream(() =>
{
var stream = file.GetStream();
file.Dispose();
return stream;
});
This seems to work just as well:
targetImage.Source = ImageSource.FromFile(file.Path);
However I feel that James' example must be showing a better way but I can't figure why -- maybe some subtle thing on one platform or another. Can anyone tell me why the Xamarin ImageSource should be set one way versus another?
The reason for choosing either FromFile() or FromStream() depends on the use case at hand. Also, the methods used depend on the data type as documented here.
WhereasFromFile() requires a string to a path, FromStream() requires a Func<System.IO.Stream>.
In the specific case you mention, and the sample hereof, it is sensible to return a Stream since a photo is being taken which is not yet stored.
First, TakePhotoAsync() is called which returns a MediaFile. This class then returns a Stream when calling GetStream(). Afterwards, the Source of the Image is set to the result.
In essence, the approach you decide on depends on the use case and data type at hand.
I usually need the element's scope which is something like $(element).scope() or angular.element(..).scope()
But now I have the opposite problem - I have a scope, and I need to find which element generated it.
How can I find out from the developers' console which element it is?
Why do I need this?
I am working on someone else's code, fixing a bug.
I am still trying to figure out some stuff, but some of the code is quite hard to follow. Very generic and a lot of copy-paste, so searches don't always help.
There's a lot of ng-includes and directives that use the parent scope.
There's a view calling a service somehow - it is unclear how yet..
I do have a reference to a scope, which is different from the one in the view that triggers the function.
So if I find the element from which that scope came from, it could sort out the relation between them etc.. At least give me some lead.
Obviously some refactoring and best practices are required in the future, but I have to focus on this bug first.
I know of nothing 'out-of-the-box', but every $scope variable has a unique $id property; and in addition, every element that has a $scope gets marked with the 'ng-scope' class. So something along the lines of the following VERY UGLY METHOD! may help (I'm assuming you have jQuery; otherwise substitute angular's jqueryLite methods):
function findById(id) {
var els = $('.ng-scope');
for (var i=0; i<els.length; i++) {
if ($(els[i]).scope().$id===id) {
return els[i];
}
}
return null;
}
And if this is actually helpful, then I feel your debugging pain.
In Marionette, afaik these two snippets achieve the same purpose:
serializeData: function() {
data = super;
data.foo = "bar";
return data;
}
and
templateHelpers: function() {
return {
foo: "bar"
}
}
What would be the difference and when to use one or the other?
In your example I can't think of any practical difference.
Semantically, though, I think that serializeData() is the better fit when you're transforming the existing model data into something else. It's more complicated to use, because you have to think about the default serialization of the model, which could include a custom model.toJSON() call. For example, your model might override toJSON to avoid sending some unneeded data to the server, but if you need that data in the view you will want to add it back with serializaData().
templateHelpers, on the other hand, is more straightforward, since all it does is add new attributes. It makes sense when there's some computed data you want to have available in the template that isn't part of your model.
In the example you cite above, I would use templateHelpers, because it's a better fit semantically and because it's simpler.
I need to use Inflector::slug() over all results fetched from my database, which are, of course, retrieved in an array. Is it possible somehow, or I'll need to loop each result and slugify it?
Thanks!
PHP's array_map() function might do what you need (although it assumes a simple indexed array).
array_map( 'Inflector::slug', $your_result )
If you're looking at something more complex, CakePHP's Set utility class may be helpful in a multi-step implementation.
I haven't tried this in a CakePHP context (i.e. mapping through a CakePHP class method), but I can't think of any reason it wouldn't work off the top of my head. Maybe it'll at least get you started.
Depending on the array you can use array_walk or array_walk_recursive.
Something like this should work.
This is for 5.3+;
array_walk_recursive($posts, function(&$value) {
$value = Inflector::slug($value);
});
If you wanted to limit it to a certain field you could also do something like this:
array_walk_recursive($posts, function(&$value, $key) {
if ($key == 'title') {
$value = Inflector::slug($value);
}
});
I haven't used Cake in a while but like Rob Wilkerson said, you might find that the Set class could make lighter work of this.