var targetPos:Number = _root.flag._x;
var amplitude:Number = 0;
// 振幅距離に対する減退する距離の割合
// 数値が大きくなるほど遅く動く (0 < deceleration < 1)
var deceleration:Number = 0.8;
// 数値が大きくなるほど鋭く動く (0 < friction)
var friction:Number = 0.5;

this.onRelease = function():Void {
    this.onEnterFrame = function():Void {
        amplitude += targetPos - this._x;
        this._x += amplitude * friction;
        amplitude *= deceleration;
        if (Math.abs(targetPos - this._x) < 0.1 && Math.abs(amplitude) < 0.1) {
            this._x = targetPos;
            delete this.onEnterFrame;
        }
    };
};