This is a simple MelonJS ObjectEntity that uses an RPG Maker spritesheet file to draw itself standing and walking in four different directions.

CharacterFromRPGMakerSpritesheet.js

game.CharacterFromRPGMakerSpritesheet = me.ObjectEntity.extend({
  init: function(x, y, settings) {
    this.parent(x, y, settings);

    this.renderable.addAnimation("stand-down", [0]);
    this.renderable.addAnimation("down", [0, 1, 2, 3], 3);

    this.renderable.addAnimation("stand-up", [12]);
    this.renderable.addAnimation("up", [12, 13, 14, 15], 3);

    this.renderable.addAnimation("stand-left", [4]);
    this.renderable.addAnimation("left", [4, 5, 6, 7], 3);

    this.renderable.addAnimation("stand-right", [8]);
    this.renderable.addAnimation("right", [8, 9, 10, 11], 3);

    this.setFriction(0.8, 0.8);
    this.setVelocity(3, 3);
    this.gravity = 0;

    me.game.viewport.follow(this.pos, me.game.viewport.AXIS.BOTH);

    this.direction = "down";
  },
  update: function () {
    if(me.input.isKeyPressed("left")) {
      this.animationspeed = 3;

      this.vel.x = -this.accel.x * me.timer.tick;
      this.renderable.setCurrentAnimation("left");
      this.direction = "left";
    } else if(me.input.isKeyPressed("right")) {
      this.animationspeed = 3;

      this.vel.x = this.accel.x * me.timer.tick;
      this.renderable.setCurrentAnimation("right");
      this.direction = "right";
    } else if(me.input.isKeyPressed("up")) {
      this.animationspeed = 3;

      this.vel.y = -this.accel.y * me.timer.tick;
      this.renderable.setCurrentAnimation("up");
      this.direction = "up";
    } else if(me.input.isKeyPressed("down")) {
      this.animationspeed = 3;

      this.vel.y = this.accel.y * me.timer.tick;
      this.renderable.setCurrentAnimation("down");
      this.direction = "down";
    }

    if(this.vel.y == 0 && this.vel.x == 0) {
      this.renderable.setCurrentAnimation("stand-" + this.direction);
    }

    var updated = this.updateMovement();

    if(updated) {
      this.parent(this);
    }
    return updated;
  }
});