code: function checkCompiling(schema, root, baseId) {
    /* jshint validthis: true */
    var index = compIndex.call(this, schema, root, baseId);
    if (index >= 0) return { index: index, compiling: true };
    index = this._compilations.length;
    this._compilations[index] = {
      schema: schema,
      root: root,
      baseId: baseId
    };
    return { index: index, compiling: false };
  }
docs: Checks if the schema is currently compiled
  @this   Ajv
  @param  {Object} schema schema to compile
  @param  {Object} root root object
  @param  {String} baseId base schema ID
  @return {Object} object with properties "index" (compilation index) and "compiling" (boolean)