Source

File: wp-includes/class-wp-customize-control.php

public function to_json() {
		$this->json['settings'] = array();
		foreach ( $this->settings as $key => $setting ) {
			$this->json['settings'][ $key ] = $setting->id;
		}

		$this->json['type']           = $this->type;
		$this->json['priority']       = $this->priority;
		$this->json['active']         = $this->active();
		$this->json['section']        = $this->section;
		$this->json['content']        = $this->get_content();
		$this->json['label']          = $this->label;
		$this->json['description']    = $this->description;
		$this->json['instanceNumber'] = $this->instance_number;

		if ( 'dropdown-pages' === $this->type ) {
			$this->json['allow_addition'] = $this->allow_addition;
		}
	}