How to use the IIRFilter?

[bowen-source]

var filter = new IIRFilter(DSP.LOWPASS, cut_fre,fs); filter.process(data);

this is my code,The help document says IIRFilter should be written like this:
var filter = IIRFilter(LOWPASS, 200, 44100); filter.process(signal);

but the code which the help document gave seems wrong ,it warns me that 'LOWPASS' is not defined ,but DSP.LOWPASS is ok,and i noice that IIRFilter actually needs 4 parameters(type,cutoff,resonance,sampleRate).

so how to use IIRFilter??