I created a minimal example here: http://britzl.github.io/publicexamples/play_animation/index.html (left, right, up, down to move). Code here: https://github.com/britzl/publicexamples/tree/master/examples/play_animation
In my example with a player character the main idea is to define one walk animation and one idle animation. The walk animation will be played when a key is pressed while the idle animation will be played when the player is no longer moving (ie no key is pressed)