8.2. JavaScript¶

Note

While every design function has access to all JavaScript objects, the table below describes appropriate usage cases. For example, you may use emit() in Map Functions, but getRow() is not permitted during Map Functions.

JS Function	Reasonable to use in design doc functions
`emit()`	Map Functions
`getRow()`	List Functions
`JSON`	any
`isArray()`	any
`log()`	any
`provides()`	Show Functions, List Functions
`registerType()`	Show Functions, List Functions
`require()`	any, except Reduce and Rereduce Functions
`send()`	List Functions
`start()`	List Functions
`sum()`	any
`toJSON()`	any

8.2.1. Design functions context¶

Each design function executes in a special context of predefined objects, modules and functions:

emit(key, value)¶

Emits a key-value pair for further processing by CouchDB after the map function is done.

Arguments:	key – The view key value – The key‘s associated value

function(doc){
    emit(doc._id, doc._rev);
}

getRow()¶

Extracts the next row from a related view result.

Returns:	View result row
Return type:	object

function(head, req){
    send('[');
    row = getRow();
    if (row){
        send(toJSON(row));
        while(row = getRow()){
            send(',');
            send(toJSON(row));
        }
    }
    return ']';
}

JSON¶: JSON2 object.

isArray(obj)¶

A helper function to check if the provided value is an Array.

Arguments:	obj – Any JavaScript value
Returns:	`true` if obj is Array-typed, `false` otherwise
Return type:	boolean

log(message)¶

Log a message to the CouchDB log (at the INFO level).

Arguments:	message – Message to be logged

function(doc){
    log('Procesing doc ' + doc['_id']);
    emit(doc['_id'], null);
}

After the map function has run, the following line can be found in CouchDB logs (e.g. at /var/log/couchdb/couch.log):

[Sat, 03 Nov 2012 17:38:02 GMT] [info] [<0.7543.0>] OS Process #Port<0.3289> Log :: Processing doc 8d300b86622d67953d102165dbe99467

provides(key, func)¶

Registers callable handler for specified MIME key.

Arguments:	key – MIME key previously defined by `registerType()` func – MIME type handler

registerType(key, *mimes)¶

Registers list of MIME types by associated key.

Arguments:	key – MIME types mimes – MIME types enumeration

Predefined mappings (key-array):

all: */*
text: text/plain; charset=utf-8, txt
html: text/html; charset=utf-8
xhtml: application/xhtml+xml, xhtml
xml: application/xml, text/xml, application/x-xml
js: text/javascript, application/javascript, application/x-javascript
css: text/css
ics: text/calendar
csv: text/csv
rss: application/rss+xml
atom: application/atom+xml
yaml: application/x-yaml, text/yaml
multipart_form: multipart/form-data
url_encoded_form: application/x-www-form-urlencoded
json: application/json, text/x-json

require(path)¶

Loads CommonJS module by a specified path. The path should not start with a slash.

Arguments:	path – A CommonJS module path started from design document root
Returns:	Exported statements

send(chunk)¶

Sends a single string chunk in response.

Arguments:	chunk – Text chunk

function(head, req){
    send('Hello,');
    send(' ');
    send('Couch');
    return ;
}

start(init_resp)¶

Initiates chunked response. As an option, a custom response object may be sent at this point. For list-functions only!

Note

list functions may set the HTTP response code and headers by calling this function. This function must be called before send(), getRow() or a return statement; otherwise, the query server will implicitly call this function with the empty object ({}).

function(head, req){
    start({
        "code": 302,
        "headers": {
            "Location": "http://couchdb.apache.org"
        }
    });
    return "Relax!";
}

sum(arr)¶

Sum arr‘s items.

Arguments:	arr – Array of numbers
Return type:	number

toJSON(obj)¶

Encodes obj to JSON string. This is an alias for the JSON.stringify method.

Arguments:	obj – JSON-encodable object
Returns:	JSON string

8.2.2. CommonJS Modules¶

Support for CommonJS Modules (introduced in CouchDB 0.11.0) allows you to create modular design functions without the need for duplication of functionality.

Here’s a CommonJS module that checks user permissions:

function user_context(userctx, secobj) {
    var is_admin = function() {
        return userctx.indexOf('_admin') != -1;
    }
    return {'is_admin': is_admin}
}

exports['user'] = user_context

Each module has access to additional global variables:

module (object): Contains information about the stored module
- id (string): The module id; a JSON path in ddoc context
- current (code): Compiled module code object
- parent (object): Parent frame
- exports (object): Export statements
exports (object): Shortcut to the module.exports object

The CommonJS module can be added to a design document, like so:

{
    "views": {
        "lib": {
            "security": "function user_context(userctx, secobj) { ... }"
        }
    },
    "validate_doc_update": "function(newdoc, olddoc, userctx, secobj) {
        user = require('views/lib/security').user(userctx, secobj);
        return user.is_admin();
    }"
    "_id": "_design/test"
}

Modules paths are relative to the design document’s views object, but modules can only be loaded from the object referenced via lib. The lib structure can still be used for view functions as well, by simply storing view functions at e.g. views.lib.map, views.lib.reduce, etc.