Source

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

public function js_value() {

		/**
		 * Filters a Customize setting value for use in JavaScript.
		 *
		 * The dynamic portion of the hook name, `$this->id`, refers to the setting ID.
		 *
		 * @since 3.4.0
		 *
		 * @param mixed                $value The setting value.
		 * @param WP_Customize_Setting $this  WP_Customize_Setting instance.
		 */
		$value = apply_filters( "customize_sanitize_js_{$this->id}", $this->value(), $this );

		if ( is_string( $value ) ) {
			return html_entity_decode( $value, ENT_QUOTES, 'UTF-8' );
		}

		return $value;
	}