three.js/examples/js/loaders/OBJLoader.js

/**
 * @author mrdoob / http://mrdoob.com/
 */

THREE.OBJLoader = function () {};
THREE.OBJLoader.prototype.load = function ( url, callback ) {

	var xhr = new XMLHttpRequest();
	xhr.onreadystatechange = function () {

		if ( xhr.readyState == 4 ) {

			if ( xhr.status == 200 || xhr.status == 0 ) {

				THREE.OBJLoader.prototype.parse( xhr.responseText, callback );

			} else {

				console.error( 'THREE.OBJLoader: Couldn\'t load ' + url + ' (' + xhr.status + ')' );

			}

		}

	};

	xhr.open( "GET", url, true );
	xhr.send( null );

};

THREE.OBJLoader.prototype.parse = function ( data, callback ) {

	var geometry = new THREE.Geometry();

	function vertex( a, b, c ) {

		return new THREE.Vector3( parseFloat( a ), parseFloat( b ), parseFloat( c ) );

	}

	function face3( a, b, c ) {

		return new THREE.Face3( parseInt( a ) - 1, parseInt( b ) - 1, parseInt( c ) - 1 );

	}

	function face4( a, b, c, d ) {

		return new THREE.Face4( parseInt( a ) - 1, parseInt( b ) - 1, parseInt( c ) - 1, parseInt( d ) - 1 );

	}

	var pattern, result;

	// v float float float
	// ["v 1.0 2.0 3.0", "1.0", "2.0", "3.0"]

	pattern = /v ([\-|\d|.]+) ([\-|\d|.]+) ([\-|\d|.]+)/g;

	while ( ( result = pattern.exec( data ) ) != null ) {

		geometry.vertices.push( vertex( result[ 1 ], result[ 2 ], result[ 3 ] ) );

	}

	// f vertex vertex vertex ...
	// ["f 1 2 3", "1", "2", "3", undefined]

	pattern = /f( [\d]+)( [\d]+)( [\d]+)( [\d]+)?/g;

	while ( ( result = pattern.exec( data ) ) != null ) {

		geometry.faces.push(
			result[ 4 ] === undefined ?
			face3( result[ 1 ], result[ 2 ], result[ 3 ] ) :
			face4( result[ 1 ], result[ 2 ], result[ 3 ], result[ 4 ] )
		);

	}

	// f vertex/uv vertex/uv vertex/uv ...
	// ["f 1/1 2/2 3/3", " 1/1", "1", "1", " 2/2", "2", "2", " 3/3", "3", "3", undefined, undefined, undefined]

	pattern = /f ([\d]+)\/([\d]+) ([\d]+)\/([\d]+) ([\d]+)\/([\d]+)/g;

	while ( ( result = pattern.exec( data ) ) != null ) {

		geometry.faces.push(
			result[ 10 ] === undefined ?
			face3( result[ 2 ], result[ 5 ], result[ 8 ] ) :
			face4( result[ 2 ], result[ 5 ], result[ 8 ], result[ 11 ] )
		);

	}

	// f vertex/uv/normal vertex/uv/normal vertex/uv/normal ...
	// ["f 1/1/1 2/2/2 3/3/3", " 1/1/1", "1", "1", "1", " 2/2/2", "2", "2", "2", " 3/3/3", "3", "3", "3", undefined, undefined, undefined, undefined]

	pattern = /f( ([\d]+)\/([\d]+)\/([\d]+))( ([\d]+)\/([\d]+)\/([\d]+))( ([\d]+)\/([\d]+)\/([\d]+))( ([\d]+)\/([\d]+)\/([\d]+))?/g;

	while ( ( result = pattern.exec( data ) ) != null ) {

		geometry.faces.push(
			result[ 13 ] === undefined ?
			face3( result[ 2 ], result[ 6 ], result[ 10 ] ) :
			face4( result[ 2 ], result[ 6 ], result[ 10 ], result[ 14 ] )
		);

	}

	// f vertex//normal vertex//normal vertex//normal ...
	// ["f 1//1 2//2 3//3", " 1//1", "1", "1", " 2//2", "2", "2", " 3//3", "3", "3", undefined, undefined, undefined]

	pattern = /f ([\d]+)\/\/([\d]+) ([\d]+)\/\/([\d]+) ([\d]+)\/\/([\d]+)/g;

	while ( ( result = pattern.exec( data ) ) != null ) {

		geometry.faces.push(
			result[ 10 ] === undefined ?
			face3( result[ 2 ], result[ 5 ], result[ 8 ] ) :
			face4( result[ 2 ], result[ 5 ], result[ 8 ], result[ 11 ] )
		);

	}

	geometry.computeCentroids();

	callback( geometry );

}