A side effect is a state change outside of setting the value.

Another common use the afterSet method is to fire some kind of change event.

<pre class="runnable readonly text 340">
/**
* Account balance
* @member {Number} balance_=0
*/
balance_: 0,

...

afterSetBalance(balance){

    if (balance < 0) this.status = this.OVERDRAWN; // Side-effect

    this.fire('balanceChange', {
        component: this,
        balance
    });

}
</pre>

