parse( object, onDone, options ) {

			if ( onDone && typeof onDone === 'object' ) {

				console.warn( 'THREE.PLYExporter: The options parameter is now the third argument to the "parse" function. See the documentation for the new API.' );
				options = onDone;
				onDone = undefined;

			} // Iterate over the valid meshes in the object


			function traverseMeshes( cb ) {

				object.traverse( function ( child ) {

					if ( child.isMesh === true ) {

						const mesh = child;
						const geometry = mesh.geometry;

						if ( geometry.isBufferGeometry !== true ) {

							throw new Error( 'THREE.PLYExporter: Geometry is not of type THREE.BufferGeometry.' );

						}

						if ( geometry.hasAttribute( 'position' ) === true ) {

							cb( mesh, geometry );

						}

					}

				} );

			} // Default options


			const defaultOptions = {
				binary: false,
				excludeAttributes: [],
				// normal, uv, color, index
				littleEndian: false
			};
			options = Object.assign( defaultOptions, options );
			const excludeAttributes = options.excludeAttributes;
			let includeNormals = false;
			let includeColors = false;
			let includeUVs = false; // count the vertices, check which properties are used,
			// and cache the BufferGeometry

			let vertexCount = 0;
			let faceCount = 0;
			object.traverse( function ( child ) {

				if ( child.isMesh === true ) {

					const mesh = child;
					const geometry = mesh.geometry;

					if ( geometry.isBufferGeometry !== true ) {

						throw new Error( 'THREE.PLYExporter: Geometry is not of type THREE.BufferGeometry.' );

					}

					const vertices = geometry.getAttribute( 'position' );
					const normals = geometry.getAttribute( 'normal' );
					const uvs = geometry.getAttribute( 'uv' );
					const colors = geometry.getAttribute( 'color' );
					const indices = geometry.getIndex();

					if ( vertices === undefined ) {

						return;

					}

					vertexCount += vertices.count;
					faceCount += indices ? indices.count / 3 : vertices.count / 3;
					if ( normals !== undefined ) includeNormals = true;
					if ( uvs !== undefined ) includeUVs = true;
					if ( colors !== undefined ) includeColors = true;

				}

			} );
			const includeIndices = excludeAttributes.indexOf( 'index' ) === - 1;
			includeNormals = includeNormals && excludeAttributes.indexOf( 'normal' ) === - 1;
			includeColors = includeColors && excludeAttributes.indexOf( 'color' ) === - 1;
			includeUVs = includeUVs && excludeAttributes.indexOf( 'uv' ) === - 1;

			if ( includeIndices && faceCount !== Math.floor( faceCount ) ) {

				// point cloud meshes will not have an index array and may not have a
				// number of vertices that is divisble by 3 (and therefore representable
				// as triangles)
				console.error( 'PLYExporter: Failed to generate a valid PLY file with triangle indices because the ' + 'number of indices is not divisible by 3.' );
				return null;

			}

			const indexByteCount = 4;
			let header = 'ply\n' + `format ${options.binary ? options.littleEndian ? 'binary_little_endian' : 'binary_big_endian' : 'ascii'} 1.0\n` + `element vertex ${vertexCount}\n` + // position
    'property float x\n' + 'property float y\n' + 'property float z\n';

			if ( includeNormals === true ) {

				// normal
				header += 'property float nx\n' + 'property float ny\n' + 'property float nz\n';

			}

			if ( includeUVs === true ) {

				// uvs
				header += 'property float s\n' + 'property float t\n';

			}

			if ( includeColors === true ) {

				// colors
				header += 'property uchar red\n' + 'property uchar green\n' + 'property uchar blue\n';

			}

			if ( includeIndices === true ) {

				// faces
				header += `element face ${faceCount}\n` + 'property list uchar int vertex_index\n';

			}

			header += 'end_header\n'; // Generate attribute data

			const vertex = new THREE.Vector3();
			const normalMatrixWorld = new THREE.Matrix3();
			let result = null;

			if ( options.binary === true ) {

				// Binary File Generation
				const headerBin = new TextEncoder().encode( header ); // 3 position values at 4 bytes
				// 3 normal values at 4 bytes
				// 3 color channels with 1 byte
				// 2 uv values at 4 bytes

				const vertexListLength = vertexCount * ( 4 * 3 + ( includeNormals ? 4 * 3 : 0 ) + ( includeColors ? 3 : 0 ) + ( includeUVs ? 4 * 2 : 0 ) ); // 1 byte shape desciptor
				// 3 vertex indices at ${indexByteCount} bytes

				const faceListLength = includeIndices ? faceCount * ( indexByteCount * 3 + 1 ) : 0;
				const output = new DataView( new ArrayBuffer( headerBin.length + vertexListLength + faceListLength ) );
				new Uint8Array( output.buffer ).set( headerBin, 0 );
				let vOffset = headerBin.length;
				let fOffset = headerBin.length + vertexListLength;
				let writtenVertices = 0;
				traverseMeshes( function ( mesh, geometry ) {

					const vertices = geometry.getAttribute( 'position' );
					const normals = geometry.getAttribute( 'normal' );
					const uvs = geometry.getAttribute( 'uv' );
					const colors = geometry.getAttribute( 'color' );
					const indices = geometry.getIndex();
					normalMatrixWorld.getNormalMatrix( mesh.matrixWorld );

					for ( let i = 0, l = vertices.count; i < l; i ++ ) {

						vertex.x = vertices.getX( i );
						vertex.y = vertices.getY( i );
						vertex.z = vertices.getZ( i );
						vertex.applyMatrix4( mesh.matrixWorld ); // Position information

						output.setFloat32( vOffset, vertex.x, options.littleEndian );
						vOffset += 4;
						output.setFloat32( vOffset, vertex.y, options.littleEndian );
						vOffset += 4;
						output.setFloat32( vOffset, vertex.z, options.littleEndian );
						vOffset += 4; // Normal information

						if ( includeNormals === true ) {

							if ( normals != null ) {

								vertex.x = normals.getX( i );
								vertex.y = normals.getY( i );
								vertex.z = normals.getZ( i );
								vertex.applyMatrix3( normalMatrixWorld ).normalize();
								output.setFloat32( vOffset, vertex.x, options.littleEndian );
								vOffset += 4;
								output.setFloat32( vOffset, vertex.y, options.littleEndian );
								vOffset += 4;
								output.setFloat32( vOffset, vertex.z, options.littleEndian );
								vOffset += 4;

							} else {

								output.setFloat32( vOffset, 0, options.littleEndian );
								vOffset += 4;
								output.setFloat32( vOffset, 0, options.littleEndian );
								vOffset += 4;
								output.setFloat32( vOffset, 0, options.littleEndian );
								vOffset += 4;

							}

						} // UV information


						if ( includeUVs === true ) {

							if ( uvs != null ) {

								output.setFloat32( vOffset, uvs.getX( i ), options.littleEndian );
								vOffset += 4;
								output.setFloat32( vOffset, uvs.getY( i ), options.littleEndian );
								vOffset += 4;

							} else if ( includeUVs !== false ) {

								output.setFloat32( vOffset, 0, options.littleEndian );
								vOffset += 4;
								output.setFloat32( vOffset, 0, options.littleEndian );
								vOffset += 4;

							}

						} // Color information


						if ( includeColors === true ) {

							if ( colors != null ) {

								output.setUint8( vOffset, Math.floor( colors.getX( i ) * 255 ) );
								vOffset += 1;
								output.setUint8( vOffset, Math.floor( colors.getY( i ) * 255 ) );
								vOffset += 1;
								output.setUint8( vOffset, Math.floor( colors.getZ( i ) * 255 ) );
								vOffset += 1;

							} else {

								output.setUint8( vOffset, 255 );
								vOffset += 1;
								output.setUint8( vOffset, 255 );
								vOffset += 1;
								output.setUint8( vOffset, 255 );
								vOffset += 1;

							}

						}

					}

					if ( includeIndices === true ) {

						// Create the face list
						if ( indices !== null ) {

							for ( let i = 0, l = indices.count; i < l; i += 3 ) {

								output.setUint8( fOffset, 3 );
								fOffset += 1;
								output.setUint32( fOffset, indices.getX( i + 0 ) + writtenVertices, options.littleEndian );
								fOffset += indexByteCount;
								output.setUint32( fOffset, indices.getX( i + 1 ) + writtenVertices, options.littleEndian );
								fOffset += indexByteCount;
								output.setUint32( fOffset, indices.getX( i + 2 ) + writtenVertices, options.littleEndian );
								fOffset += indexByteCount;

							}

						} else {

							for ( let i = 0, l = vertices.count; i < l; i += 3 ) {

								output.setUint8( fOffset, 3 );
								fOffset += 1;
								output.setUint32( fOffset, writtenVertices + i, options.littleEndian );
								fOffset += indexByteCount;
								output.setUint32( fOffset, writtenVertices + i + 1, options.littleEndian );
								fOffset += indexByteCount;
								output.setUint32( fOffset, writtenVertices + i + 2, options.littleEndian );
								fOffset += indexByteCount;

							}

						}

					} // Save the amount of verts we've already written so we can offset
					// the face index on the next mesh


					writtenVertices += vertices.count;

				} );
				result = output.buffer;

			} else {

				// Ascii File Generation
				// count the number of vertices
				let writtenVertices = 0;
				let vertexList = '';
				let faceList = '';
				traverseMeshes( function ( mesh, geometry ) {

					const vertices = geometry.getAttribute( 'position' );
					const normals = geometry.getAttribute( 'normal' );
					const uvs = geometry.getAttribute( 'uv' );
					const colors = geometry.getAttribute( 'color' );
					const indices = geometry.getIndex();
					normalMatrixWorld.getNormalMatrix( mesh.matrixWorld ); // form each line

					for ( let i = 0, l = vertices.count; i < l; i ++ ) {

						vertex.x = vertices.getX( i );
						vertex.y = vertices.getY( i );
						vertex.z = vertices.getZ( i );
						vertex.applyMatrix4( mesh.matrixWorld ); // Position information

						let line = vertex.x + ' ' + vertex.y + ' ' + vertex.z; // Normal information

						if ( includeNormals === true ) {

							if ( normals != null ) {

								vertex.x = normals.getX( i );
								vertex.y = normals.getY( i );
								vertex.z = normals.getZ( i );
								vertex.applyMatrix3( normalMatrixWorld ).normalize();
								line += ' ' + vertex.x + ' ' + vertex.y + ' ' + vertex.z;

							} else {

								line += ' 0 0 0';

							}

						} // UV information


						if ( includeUVs === true ) {

							if ( uvs != null ) {

								line += ' ' + uvs.getX( i ) + ' ' + uvs.getY( i );

							} else if ( includeUVs !== false ) {

								line += ' 0 0';

							}

						} // Color information


						if ( includeColors === true ) {

							if ( colors != null ) {

								line += ' ' + Math.floor( colors.getX( i ) * 255 ) + ' ' + Math.floor( colors.getY( i ) * 255 ) + ' ' + Math.floor( colors.getZ( i ) * 255 );

							} else {

								line += ' 255 255 255';

							}

						}

						vertexList += line + '\n';

					} // Create the face list


					if ( includeIndices === true ) {

						if ( indices !== null ) {

							for ( let i = 0, l = indices.count; i < l; i += 3 ) {

								faceList += `3 ${indices.getX( i + 0 ) + writtenVertices}`;
								faceList += ` ${indices.getX( i + 1 ) + writtenVertices}`;
								faceList += ` ${indices.getX( i + 2 ) + writtenVertices}\n`;

							}

						} else {

							for ( let i = 0, l = vertices.count; i < l; i += 3 ) {

								faceList += `3 ${writtenVertices + i} ${writtenVertices + i + 1} ${writtenVertices + i + 2}\n`;

							}

						}

						faceCount += indices ? indices.count / 3 : vertices.count / 3;

					}

					writtenVertices += vertices.count;

				} );
				result = `${header}${vertexList}${includeIndices ? `${faceList}\n` : '\n'}`;

			}

			if ( typeof onDone === 'function' ) requestAnimationFrame( () => onDone( result ) );
			return result;

		}
https://github.com/gkjohnson/ply-exporter-js

Usage:
 const exporter = new PLYExporter();

 // second argument is a list of options
 exporter.parse(mesh, data => console.log(data), { binary: true, excludeAttributes: [ 'color' ], littleEndian: true });

Format Definition:
http://paulbourke.net/dataformats/ply/