Example customizer select control

control-select.php

<?php

class Hybrid_Customize_Control_Select extends WP_Customize_Control {

	public $type = 'select-custom';

	public function to_json() {
		parent::to_json();

		$this->json['choices'] = $this->choices;
		$this->json['link']    = $this->get_link();
		$this->json['value']   = $this->value();
	}

	public function content_template() { ?>

		<# if ( ! data.choices ) {
			return;
		} #>

		<label>

			<# if ( data.label ) { #>
				<span class="customize-control-title">{{ data.label }}</span>
			<# } #>

			<# if ( data.description ) { #>
				<span class="description customize-control-description">{{{ data.description }}}</span>
			<# } #>

			<select {{{ data.link }}}>

				<# _.each( data.choices, function( label, choice ) { #>

					<option value="{{ choice }}" <# if ( choice === data.value ) { #> selected="selected" <# } #>>{{ label }}</option>

				<# } ) #>

			</select>
		</label>
	<?php }
}