index.js

if (typeof AFRAME === 'undefined') {
  throw new Error('Component attempted to register before AFRAME was available.');
}

/**
 * Fence component for A-Frame.
 *
 * Thanks to Don McCurdy <https://github.com/donmccurdy>
 * for his initial code
 * and ngokevin's Component Boilerplate <https://github.com/ngokevin/aframe-component-boilerplate>
 *
 */
AFRAME.registerComponent('fence', {
  schema: {
      width: {
          type: 'number',
          default: 10
      },
      depth: {
          type: 'number',
          default: 10
      },
      x0: {
          type: 'number',
          default: 0
      },
      z0: {
          type: 'number',
          default: 0
      }
  },


  tick: function() {
      var data = this.data;
      var thiswidth = data.width;
      var thisdepth = data.depth;
      var x0 = data.x0;
      var z0 = data.z0;

      minX = thiswidth / 2 + x0;
      maxX = ( -1 * thiswidth / 2 ) + x0;

      minZ = thisdepth / 2 + z0;
      maxZ = ( -1 * thisdepth / 2 ) + z0;

      var position = this.el.getAttribute('position');

      position.x = Math.min( minX, position.x);
      position.x = Math.max( maxX, position.x);

      position.z = Math.min( minZ, position.z);
      position.z = Math.max( maxZ, position.z);

      this.el.setAttribute('position', position);
  },

});