Javascript Date.prototype.toJSON() or Date.prototype.toISOString()

I just found out that Date.prototype.toJSON() returns string format same as Date.prototype.toISOString(), why do we have them both? I did not know which community to add this on, so please suggest if any community is targeted for it. Where do I questions like these? It was good that, I had Mozilla DN, otherwise, I don’t know where to post these.