quick'n'dirty conversor from OSM xml to GeoJSON using d3

parse_osm.js

// you should use https://github.com/tyrasd/osmtogeojson if you are gonna build something real

function osm2geojson(xml) {
  var parser = new DOMParser();
  var doc = parser.parseFromString(xml, 'text/xml');

  var points =  {}

  d3.select(doc).selectAll('node').each(function() { 
    var n = d3.select(this)
    points[n.attr('id')] = [+n.attr('lon'), +n.attr('lat')]
  })

  var features = [];

  d3.select(doc).selectAll('way').each(function() { 
    var type = "LineString"
    var way = d3.select(this)
    var refs = []
    var properties = {}
    way.selectAll('nd').each(function() { refs.push(d3.select(this).attr('ref')) })
    way.selectAll('tag').each(function() { 
      var t = d3.select(this);
      properties[t.attr('k')] = t.attr('v');
    })
    var coordinates = refs.map(function(r) { return points[r]; })
    if (refs[0] === refs[refs.length - 1]) {
      type = "Polygon"
      coordinates = [ coordinates ]
      // poygon
    }
    if( coordinates && coordinates.length) {
      features.push({
        type: "Feature",
        geometry: {
          type: type,
          coordinates: coordinates
        },
        properties: properties
      })
    }
  })

  return features;
}