Example code, packaged as a plugin for my Torque article on getting posts via GET requests using the WordPress REST API. http://torquemag.io/?p=72403

mini-rest-api-get-client.php

<?php
/*
Plugin Name: JP Mini REST API GET Client
Plugin URI: http://torquemag.io/?p=72403
Description: A min client for making GET requests via the WordPress REST API.
Version: 0.1.1
Author: Josh Pollock
Author URI: http://JoshPress.net
License: GPL v2 or later
*/

/**
 * Makes a GET request to the WP REST API & returns JSON Object
 *
 * @param string $url URL to GET
 *
 * @return array|WP_Error Array of post objects on success or WP_Error object on failure.
 */
function jp_mini_rest_get_json( $url ) {
	//GET the remote site
	$response = wp_remote_get( $url );

	//Check for error
	if ( is_wp_error( $response ) ) {
		return sprintf( 'The URL %1s could not be retrieved.', $url );
	}

	//get just the body
	$data = wp_remote_retrieve_body( $response );

	//return if not an error
	if ( ! is_wp_error( $data )  ) {

		//decode and return
		return json_decode( $data );

	}

}

/**
 * Builds a URL string for making GET requests for the WP REST API
 *
 * @see http://wp-api.org/#posts_retrieve-posts
 *
 * @param string|array $post_types Post type(s) to query for. Can be on post type as a string or an array of post types. Default is 'post'
 * @param bool|array   $filters Optional. Filters to use in query. Should be an array in form of filter => value. See REST API docs for possible values. The default is false, which skips adding filters.
 * @param string $base Optional. Base for making request. Default is 'wp-json/posts?
 *
 * @return string|void
 */
function jp_mini_rest_posts_url_string( $post_types = 'post', $filters = false, $rooturl = 'home_url', $base = '/wp-json/posts?' ) {
	if ( is_callable( $rooturl ) ) {
		$url = call_user_func( $rooturl );
		$url = $url.$base;
	}
	else {
		$url = $rooturl.$base;
	}

	if ( is_string(  $post_types ) ) {
		$post_types = array( $post_types);
	}
	foreach ( $post_types as $type ) {
		$url = add_query_arg( "type[]", $type, $url  );
	}

	if ( $filters ) {

		foreach( $filters as $filter => $value ) {
			$args[ "filter[{$filter}]" ] =  $value;
		}
		$url = add_query_arg( $args, $url );
	}

	return $url;

}