These are the relevant bits to filter the output from a phantomjs instance when it's dumping out warnings from the old Qt library on OS X 10.9 Mavericks, since the phantom lib doesn't look to be getting updated for another 3 months or so.

warnings-filtered-out-of-phantomjs-stream.js

var  stream = require('stream'),
       util = require('util');
       
 
function FilterThirdPartyWarnings(options){
	// allow use without new
	if (!(this instanceof FilterThirdPartyWarnings)) {
		return new FilterThirdPartyWarnings(options);
	}
	stream.Transform.call(this, options);
};
 
util.inherits(FilterThirdPartyWarnings, stream.Transform);
 
FilterThirdPartyWarnings.prototype._transform = function(chunk, encoding, done){
	var self = this;
 
	if(self.decodeStrings === false){
		var data = chunk; // this chunk is a string
	} else {
		var data = chunk.toString(); // this chunk is a buffer
	}
 
	if (self._lastLineData) { data = self._lastLineData + data; }
 
	var lines = data.split('\n');
 
	self._lastLineData = lines.splice(lines.length-1,1)[0]; // save the last line of data
 
	lines.map(function(value){
		if(value.match(/\*\*\* WARNING|CoreText/g)){ // skips the data if it's found to have a warning
			return;
		}
		// otherwise push it back to the stack
		self.push(value+'\n', encoding);
	});
 
	done();
};
 
// when done with the filtering, push the last line of data out too
FilterThirdPartyWarnings.prototype._flush = function (done) {
	if (this._lastLineData) {
		if(this._lastLineData.match(/\*\*\* WARNING|CoreText/g)){ // skips the data if it's found to have a warning
			this.push('');
		} else {
			this.push(this._lastLineData);
		}
	}
	this._lastLineData = null;
	done();
};
 
function spawnPhantomJS(cmdPath, args) {
  var phantomjs = spawn(cmdPath, args),
      outFilter = new FilterThirdPartyWarnings( { objectMode:true } );
      errFilter = new FilterThirdPartyWarnings( { objectMode:true } );
  phantomjs.stdout.pipe(outFilter).pipe(process.stdout);
  phantomjs.stderr.pipe(errFilter).pipe(process.stdout);
  phantomjs.on('exit', function(code){
    if (code === 127) { print("Perhaps phantomjs is not installed?\n"); }
    process.exit(code);
  });
}