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Yaap is a generic annotation processor for javascript. It can be used to implement cross-cutting concerns and inject additional aspect oriented code.

It integrates with wire.js (part of cujo.js), which enables Spring-style wiring (i.e. dependency injection) of your javascript applications. With the yaap/wire plugin, @Autowired applications are possible


The Yaap-library can process annotated javascript-objects. One simply defines the object adds annotations and let Yaap process it.

The library already includes some so-called annotation processors, e.g. @NotNull or @Default, which injects a default value in case of a missing or null-argument.

var logger = {
    log: function(message, /*@Defaul("INFO")*/ level){
        console.log(level + ": " + message);

The level-parameter is annotated with @Default. Calling yaap.process scans and enables attached annotations.

logger.log("hello world"); //will print "INFO: hello world"
logger.log("hello world", "ERROR"); //will print "ERROR: hello world"

Annotations in Javascript

Javascript does not have annotations, but at specific positions, comments are saved and can be retrieved during runtime. This library allow to retrieve and parse annotations placed at these positions.

Right now, Yaap supports parameter-annotations and function-annotations:

var obj = {
    fn: function(message, /*@Defaul("INFO")*/ level) /*@NotNull*/{
        console.log(level + ": " + message);

@Default here is an parameter-annotation while @NotNull is a function-annotation. (@NotNull can also be used as parameter-annotation though).


Yaap is no library of pre-defined annotations for javascript (though some are already contained examplary). It should be an extensible foundation to process your own annotations easily. All need to be done is to register your processor. The rest is taken care of by Yaap.

var myProcessor = {
    annotation: "@NotNull",
    processFunction: function(object, fnDescription, configuration){... },
    processParameter: function(object, fnDescription, paramDescription, configuration){...}

After registering your processor, processFunction will be called, if a function is annotated with the according annotation. processParameter is called, if an annotated parameter is found. (The current @NotNull implementation uses meld.js to inject additional code)

Remark: You can either define both or one of these functions, depending on where you want to allow your annotation to be placed.

wire.js Integration

To use @Autowired (and annotations in general) in wire.js, simply add it as a plugin:

var wire = require("wire");
    level: "INFO",
    logger: {create: './Logger'},

    plugins: [
        {module: "yaap/wire"}
}, {require: require}).then(function(ctx){
}, console.error);

Everything else is done by yaap, so you can start use your annotations:

module.exports = {
  log: function(message, /*@Autowire*/ level){
        console.log(level + ": " + message);

level references the value in the wire-context (with value "INFO") now. Remark: Yaap/wire uses the parameter name to autowire. You can also supply a reference name with /*@Autowire("level")*/ Remark: You can also annotate the whole function with @Autowire so every parameter will be autowired by name.

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