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What are the differences and similarities between QML and Javascript?
I am doing research on it, as I will probably give of a small presentation about QML soon. I have already looked at it on wikipedia, but I was hoping to get some answers from people with experience.
Note: I know some QML, I don't know any Javascript.
QML is a declarative language describing a tree of objects (in the QtQuick case a tree of visual items). The documentation has a fairly comprehensive documentation of the language. QML is used in the Qt framework only.
Javascript is an imperative language. Javascript is a very popular language used in many different places, for example embeddded in HTML sites or as part of node.js servers.
QML can actually include Javascript snippets, for example for bindings and signal handlers.
QML and Javascript serve very different purposes, so I don't see how to provide a list of similarities and differences.
Getting some downvotes there, my guess is that it is because you didn't research enough before coming here. And possibly because it doesn't sound like you are quite ready for a presentation on these languages.
But I'll see if I can at least point you in the right direction; QML is what is called a "markup language", not unlike XML, whereas Javascript is an "imperative language", like many others such as Python, C and Rust. More similar to Python, as it is also an "interpreted" language, whereas the others mentioned are "compiled" languages.
Hope it helps!
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I am not able to understand why and in what kind of scenario I would like to run scripting language inside JVM at server side. I mean we already have great libraries available in JAVA... why wouldn't I use use them to do stuff instead of running scripts in JVM?
Please help me understand this concept, Can someone please tell me one or two use cases where running scripting in JVM at server side will have advantages over using JAVA libraries.
The more general question here is "Why would I want to execute code in <some scripting language> in Java?", where Javascript is simply one example of such a language.
Quoting this article:
Some Java applications' requirements make integration with a scripting language necessary. For example, your users may need to write scripts that drive the application, extend it, or contain loops and other flow-control constructs. In such cases, it's sensible to support a scripting language interpreter that can read user scripts, then run them against your Java application's classes.
Basically: if you want to allow your users to customize your application in a way that requires the richness of a programming language.
Why Javascript specifically? That depends upon your application. There may be reasons to pick that (e.g. your target users already know Javascript), or not (e.g. Lua is more popular for scripting in the games industry).
One use i can think of is:
Javascript engine can be used to evaluate arithmetic expressions
which are in a String format.
example :: String expression = "2+4";
The below is the link to a example which uses java script engine to do this.
https://stackoverflow.com/a/3423360/4626402
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In relation to this stack overflow question, I'm wondering what the typical use-cases are for compile-to-JavaScript tools. I've done some research and I've found a list of programming languages that compile to JavaScript, many of which are strongly-typed.
Emscripted and ASM.JS are typically used for for processor intensive tasks. Is this the primary use case of such tools, or is this dependent on the tool?
For the most part it is dependent on the tool. Libraries such as asm.js offer low-level complex functionality and enhancements that most people would not be able to implement themselves. This is the basis for most libraries, it brings the saying "Standing on the shoulders of giants" to mind.
CoffeeScript and TypeScript are dialects of JavaScript that offer people the option of writing in a language that has features they are accustomed to in other languages (like static typing). They can then compile their CoffeeScript code to JavaScript for use in a web browser.
I hope this gave some insight into your question.
Can compile-to-JavaScript tools be used for “regular” client-side development?
Coffeescript / TypeScript -> Yes. In fact that is on of their main
target audience.
Asm.js -> Depends on how you define regular. If creating a quake clone in the browser is regular for you then yes. If creating a standard SPA (angular/react/ember etc) is regular then no, asm.js is not targetted at you
I think most or all of those "languages that compile to JS" don't have anything to do with ASM.JS. ASM.JS is a very limited subset of JS that only runs assembly-style commands on a block of memory.
The main reason for doing so is performance, yes, since you can't directly access DOM and other handy browser objects directly.
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As far as I know, JavaScript can be used to do everything that is possible in Scheme.
Every functional programming paradigm I've learnt in Scheme is doable in JavaScript.
I know that one may end up using JavaScript to write ungood code (ones with global variables, too many states and side effects) where as Scheme restricts one to write functional code.
But apart from that, is it really necessary to use Scheme anywhere over JavaScript?
For those of you who say JavaScript can be interpreted only on a browser kindly draw the same question to Python and Scheme.
Let me pose a similar question:
Is there a reason to use French over English? Anything that you can express in French you can express in English, so is it really necessary to use French over English? Kindly draw the same question to Russian, German, Spanish, or any other spoken language you choose.
No programming language is completely unique, anything you can do in one language can be done in a different language, some implementations might require a bit more creative thought but it can still be done.
Some reasons to use Scheme instead of JavaScript or Python:
You appreciate the simplistic and minimalist structure of the
language
Ease of implementation when compared to expressive power (lambda
expressions)
You are more familiar with Scheme
The client has existing code in Scheme
Specific implementations or algorithms might have a min/max calculation available to give exact benchmarks, but you would have to look at specific algorithms. In general there is no way to define one language as always better in all situations (or even 'never worse'), and trying to pigeon hole oneself into a single language is dangerous. In my opinion, open mindedness is one of the biggest strengths a programmer can have. Being able and willing to use different languages or techniques can be a powerful tool.
I personally suggest further reading by looking up Polyglot Programming. It isn't directly related to your question, but it is a mentality that speaks to the benefits of knowing and using a variety of languages.
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I am going to work on my new project where client has demanded to use 'Lua' if possible, I have never used it before and by searching on it I found it is fast compare to javascript and getting popular nowadays.
As I am very confused I had never use it before so I want to know something
Is it really better(in terms of performance and use) then javascript?
Will I get enough resources(because I don't want to move over after starting development due to lack of resources or it becomes hard to me develop)?
Will it needed anything other than C compiler to run?
Please guys it is really important to know about such thing before starting. Any help will be appreciated.
I'm assuming you're writing a standalone application in C or C++, and you're looking for a language to enable people to extend that application by embedding another language. That's pretty much Lua's territory.
Lua's strong point is that it's very easy to embed in your (C) application. It compiles quickly, it's tiny, licensing is liberal and using C functions from Lua is relatively easy. Standard Lua has enough performance for most things you'd use a language like this for; if you need more raw speed you could look into LuaJIT, the JIT-compiler for Lua.
As for your questions:
LuaJIT will probably be pretty much as fast as you can get for a dynamic language. Lua is used in games (Sim City, Far Cry, World of Warcraft), where performance is very important.
If by 'resources' you mean documentation: sure. Lua is a very simple language, much simpler than JavaScript; the manual should help you get started with the language itself, the wiki is tasty for tips about the embedding process. This article has an example you can copy/paste.
Lua pretty much runs everywhere a C program will run. It doesn't even need an operating system, and it doesn't depend on anything at runtime if you bundle it correctly.
Embedding a full JavaScript environment in your application, and interfacing your application to the JS environment, can be a lot of work (even though Google's V8 engine has some functionality to help you; see here).
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I have a JS script (widget) which is added to other websites. Technically its similar to Google analytics. My question is: what are your advices for ensuring robustness, keeping the code from interfering with other code on the site, avoiding errors for users etc. In general, what should I know to write a professional grade widget.
Notes:
I can't use any JS library such as jquery etc..
I am a big fan of Peter Michaux's guide on how he writes javascript widgets
Also useful are Christian Heilmann's script configuration and the module pattern
Those are generic javascript articles and aren't specific to a single library
Other useful tricks are things like wrapping your code in an anonymous function to stop it interfering with other global libraries.
(function() {
//Your code goes in here
})();
Regarding errors and best practice, John Resig has an interesting article on javascript strict that isn't in yet, but does have some handy information on the sort of things you should be avoiding.
If you're still coming to terms with scoping within your objects, then you might find this article on private and public variables useful as well a a bit more technical definition by Douglas Crockford
Finally, remember to run your completed code through a code quality tool