toJSON() {
            return {
                model: 'Layer',
                inputSize: this.inputSize,
                outputSize: this.outputSize,
                regularization: this.regularization,
                epsilon: this.epsilon,
                activation: this.activation,
                W: this.W,
                b: this.b
            };
        }
@private
Export the current layer to JSON.
@return {object} model