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JavaScript Backend

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brett hartshorn edited this page Aug 9, 2015 · 17 revisions

gotchas

  • a list and tuple are the same type, both are translated into regular javascript arrays.
  • methods can not be directly passed as callback functions, because in javascript you need to worry about the calling-context-of-this. To properly pass a method as a callback use bind like this: F( ob.mymethod.bind(ob) ) where F is a function that takes a callback.
  • dictionary (object) keys are always strings, however the builtin method mydict.keys() will return an array of numbers if all the keys are string integers, this allows you to do things like max( mydict.keys() ) to get the key of the highest number.
  • class attributes must be accessed using their class names like this MyClass.somevar, you can not use this form self.somevar.
  • when using external libraries, you must use new SomeClass() to create instances.
  • python is a very type safe language, while javascript is not. In regular python 1+"2" will raise TypeError: unsupported operand type(s) for +: 'int' and 'str'. While in javascript 1+"2" causes no error at all, and instead returns "12". The transpiler currently does not check for these types of mistakes, so it is up to you to not make them. As a workaround you can use static typing, and trap type errors when calling functions.

workaround for bad javascript type safety

javascript allows you to create c which becomes "12" and is an error, a runtime error will be raised when c is passed to somefunc because it requires an integer.

def somefunc( x:int ):
  ...
a = 1
b = "2"
c = a + b
somefunc( c )

specialized syntax

features

  • multiple inheritance
  • operator overloading (explicit)
  • function and class decorators
  • getter/setter function decorators
  • list comprehensions
  • regular and lambda functions
  • function calls with *args and **kwargs

Language Keywords

  • global, nonlocal
  • while, for, continue, break
  • if, elif, else,
  • switch, case
  • try, except, raise
  • def, lambda
  • new, class
  • from, import, as
  • pass, assert
  • and, or, is, in, not
  • return, yield

HTML DOM Iterables

for item in iterable

  • NodeList
  • FileList
  • ClientRectList
  • DOMSettableTokenList
  • DOMStringList
  • DataTransferItemList
  • HTMLCollection
  • HTMLAllCollection
  • SVGElementInstanceList
  • SVGNumberList
  • SVGTransformList

Operator Overloading

TODO

  • add
  • mul

builtins

  • dir
  • type
  • hasattr
  • getattr
  • setattr
  • issubclass
  • isinstance
  • dict
  • list
  • tuple
  • int
  • float
  • str
  • round
  • range
  • sum
  • len
  • map
  • filter
  • min
  • max
  • abs
  • ord
  • chr
  • open (nodejs only)

List

  • list.append
  • list.extend
  • list.remove
  • list.insert
  • list.index
  • list.count
  • list.pop
  • list.len
  • list.contains
  • list.getitem
  • list.setitem
  • list.iter
  • list.getslice

Set

  • set.bisect
  • set.difference
  • set.intersection
  • set.issubset

String

  • str.split
  • str.splitlines
  • str.strip
  • str.startswith
  • str.endswith
  • str.join
  • str.upper
  • str.lower
  • str.index
  • str.find
  • str.isdigit
  • str.format
  • str.getitem
  • str.len
  • str.getslice

Dict

  • dict.copy
  • dict.clear
  • dict.has_key
  • dict.update
  • dict.items
  • dict.keys
  • dict.get
  • dict.set
  • dict.pop
  • dict.values
  • dict.contains
  • dict.iter
  • dict.len
  • dict.getitem
  • dict.setitem
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