LiveScript

For the primary web scripting language initially known as LiveScript, see JavaScript.

LiveScript is a functional language that compiles to JavaScript. It was created by Jeremy Ashkenas—the creator of CoffeeScript—along with Satoshi Muramaki, George Zahariev, and many others. Notably, LiveScript was briefly the name of JavaScript in 1990s.

Syntax

LiveScript is an indirect descendant of and is partly compatible with Coffeescript. The following is a fully Coffeescript-compatible hello-world example of LiveScript syntax.

hello = ->
  console.log 'hello, world!'

While calling a function can be done with empty parens, hello(), LiveScript treats the exclamation mark as a single-character shorthand for function calls with zero arguments: hello!

LiveScript introduces a number of other incompatible idioms:

Name mangling

At compile time, the LiveScript parser implicitly converts dashed variable- and function names to camelcase.

hello-world = ->
  console.log 'Hello, World!'

With this definition, both the following calls are valid. However, calling using the same dashed syntax is recommended.

hello-world!
helloWorld!

This does not preclude developers from using camelcase explicitly or using snakecase. Dashed naming is however, common in idiomatic LiveScript

Pipes

Like a number of other functional programming languages such as F# and Elixir, LiveScript supports the pipe operator, |> which passes the result of the expression on the left of the operator as the first argument to the expression on the right of it.

"hello!" |> capitalize |> console.log
# > Hello!

Operators as functions

When parenthesized, operators such as not or + can be included in pipelines or called as if they were functions.

111 |> (+) 222
# > 333

(+) 1 2
# > 3

Typing

By default, LiveScript shares the weak, dynamic typing of Coffee- and JavaScript. However, the LiveScript compiler provides optional strong typing through the --const flag.

num = 1
fun = (non-string) ->
  non-string = non-string.to-string!
fun num

While perfectly permissible by default, when the --const flag is used, the above will cause a compiler error of: [SyntaxError: redeclaration of constant "num" on line 4]. This happens because the --const option simply treats all values as if they were declared as constants, at compile time, without using the not widely supported const keyword in the output JavaScript.

External links

• LiveScript website