Callbacks in node.js

Question

I've read and heard that I shouldn't return values in functions because it is a blocking operation and that it will potentially refuse any requests until the operation has finished.

So here's a small function I've coded and I'd like to know if I am handling it correctly. I'm saying this because I just started using node and I want to code in the correct way, also because it feels weird to have a testing condition inside the function and another one to test the callback.

function isWithinSplit(path, target, separator, callBack)
{
var response = "";
var readStream = fs.createReadStream(path);

readStream.on('data', function (data) {
    response += data;
});

//Data complete, process it
readStream.on('end', function (close) 
{
    var array = response.split(separator);

    for (var idx=0 ; idx < array.length; idx++)  
    {
        if(array[idx] != "" && array[idx] == target)
            callBack("true");
        else
            callBack("false");
    }
});

}

Call:

fileHelper.isWithinSplit(__dirname + ROOM_LIST_PATH, "hello", "|", function(data){
  if(data == "true")
    console.log("hurray!");
});

I just want to know if this is how people do and if it's efficient.

Raynos · Accepted Answer · 2011-12-29 20:47:03Z

You forgot

error handling
using ===
caching array length
naming anonymous functions

function isWithinSplit(path, target, separator, callBack) {
    var response = "";
    var readStream = fs.createReadStream(path);

    readStream.on('data', function _aggregateData(data) {
        response += data;
    });

    //Data complete, process it
    readStream.on('end', function _findTarget(close) {
        var array = response.split(separator);

        for (var idx = 0, len = array.length; idx < len; idx++) {
            if (array[idx] === target) {
                return callBack(null, true);
            }
        }
        callback(null, false);
    });

    readStream.on('error', callBack);
}

fileHelper.isWithinSplit(__dirname + ROOM_LIST_PATH, "hello", "|", printIfSuccess);

function printIfSuccess(err, data) {
    if (data === true) {
        console.log("hurray!");
    }
}

You can also improve it using Array.prototype.any

readStream.on('end', function(close) {
    callback(null, response.split(seperator).any(function _doesItMatchTarget(val) {
        return val === target;
    }));
});

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