JavaScript Compiler

Compilation and Macros

Erlang JavaScript/OTP Parse Transform has two modes defined by jsmacro and js Erlang module attributes. The first mode precompiles Erlang module functions into JavaScript strings. The second one exports Erlang functions into a separate JavaScript file ready to run in the browser or Node.js.

Sample usage of jsmacro and js:

-module(sample). -compile({parse_transform, shen}). -jsmacro([tabshow/0,doc_ready/1,event/3]). -js(doc_ready/1).

Erlang Macro Functions

Macro functions are useful for using N2O as a server-side framework. Functions get rewritten during Erlang compilation into a JavaScript format string ready for embedding. Here is an example from N2O pages:

tabshow() -> X = jq("a[data-toggle=tab]"), X:on("show", fun(E) -> T = jq(E:at("target")), tabshow(T:attr("href")) end). doc_ready(E) -> D = jq(document), D:ready(fun() -> T = jq("a[href=\"#" ++ E ++ "\"]"), T:tab("show") end). event(A,B,C) -> ws:send('Bert':encodebuf( [{source,'Bert':binary(A)}, {x,C}, {pickle,'Bert':binary(B)}, {linked,C}])). main() -> Script1 = tabshow(), Script2 = event(1, 2, 3), Script3 = doc_ready(wf:js_list("tab")), io:format("tabshow/0:~n~s~nevent/3:~n~s~ndoc_ready/1:~n~s~n", [Script1,Script2,Script3]).

Perform compilation and run tests:

$ erlc sample.erl $ erl > sample:main().

You’ll get the following output:

tabshow/0: var x = $('a[data-toggle=tab]'); x.on('show',function(e) { var t = $(e['target']); return tabshow(t.attr('href')); }); event/3: ws.send(Bert.encodebuf({source:Bert.binary(1), x:3, pickle:Bert.binary(2), linked:3})); doc_ready/1: var d = $(document); d.ready(function() { var t = $('a[href="#' + 'tab' + '"]'); return t.tab('show'); });

As you see, no source-map needed.

JavaScript File Compilation

Export Erlang function to JavaScript file with -js([sample/0,fun_args/2]). You could include functions for both macro and js definitions.

Mapping Erlang/OTP to JavaScript/OTP

Following OTP libraries are partially supported in Erlang JavaScript Parse Transform: lists, proplists, queue, string.

Example 1

S = lists:map(fun(X) -> X * X end,[1,2,3,4]),

transforms to:

s = [1,2,3,4].map(function(x) { return x * x; });

Example 2

M = lists:foldl(fun(X, Acc) -> Acc + X end,0,[1,2,3,4]),

transforms to:

m = [1,2,3,4].reduce(function(x,acc) { return acc + x; },0);

 




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