Expose featureCount property. Fixes #40.

README.md

@@ -101,6 +101,10 @@ Calling [shapefile.open](#open) yields a *source*; you can then call [*source*.r
 
 The shapefile’s bounding box [*xmin*, *ymin*, *xmax*, *ymax*], where *x* and *y* represent longitude and latitude in spherical coordinates. This field is only defined on sources returned by [shapefile.open](#open) and [shapefile.openShp](#openShp), not [shapefile.openDbf](#openDbf).
 
+<a name="source_size" href="#source_size">#</a> <i>source</i>.<b>size</b>
+
+The number of features present, determined by looking at the header of the .dbf file. This field is only defined on sources returned by [shapefile.open](#open) and [shapefile.openDbf](#openDbf), not [shapefile.openShp](#openShp).
+
 <a name="source_read" href="#source_read">#</a> <i>source</i>.<b>read</b>() [<>](https://github.com/mbostock/shapefile/blob/master/shapefile/read.js "Source")
 
 Returns a Promise for the next record from the underlying stream. The yielded result is an object with the following properties:

dbf/index.js

@@ -17,6 +17,7 @@ function Dbf(source, decoder, head, body) {
   this._source = source;
   this._decode = decoder.decode.bind(decoder);
   this._recordLength = head.getUint16(10, true);
+  this.size = head.getUint16(4, true);
   this._fields = [];
   for (var n = 0; body.getUint8(n) !== 0x0d; n += 32) {
     for (var j = 0; j < 11; ++j) if (body.getUint8(n + j) === 0) break;

shapefile/index.js

@@ -16,6 +16,7 @@ function Shapefile(shp, dbf) {
   this._shp = shp;
   this._dbf = dbf;
   this.bbox = shp.bbox;
+  this.size = dbf && dbf.size;
 }
 
 var prototype = Shapefile.prototype;