Help fix this legendary wizard's buggy spell-casting code! Identify the three bugs and type the correct fixes below.
function castSpell(spellName) {
var mana = 100;
if (spellName = "fireball") {
mana = mana - 30
console.log("Casting fireball!")
} else if (spellName == "iceblast") {
mana -= 40;
console.log("Casting iceblast!");
} else {
console.log("Unknown spell...");
}
return mana;
}