Javelins and throwing-spears seem to have been the most common and important weapons in early Irish warfare. Literary and historical accounts of battles or the equipment of individual warriors emphasize the use of thrown projectiles in the initial stages of a battle. This literary description of the future king Áed Alláin in the Fragmentary Annals of Ireland gives us a description of the typical equipment of a wealthy warrior-aristocrat:
...all inside were snoring as if they were dead, except for the king's son himself, and this is how he was sleeping: in his royal bed, as if he were waiting for battle, with a great shield on his left side, and two huge javelins on his right side, a long gold-hilted inlaid sword on his thigh...
So multiple, heavy javelins appear to have been considered an essential part of an Irish warrior's kit. Other descriptions of battles during the 9th-10th centuries frequently mention the sound of javelins being thrown as a ubiquitous sound of battle, like the clashing of swords or the sound of shields crashing together:
Then the battle was fought hard. The shrieking of the javelins, and the crashing blows of swords, and the hammering of shields being struck, and the cries of soldiers being overcome, were loudly audible.
Interestingly, the Fragmentary Annals seem to imply that the Irish were particularly adept at wielding spears and throwing javelins, to the extent that a foreigner being able to use these weapons in the same capacity as an Irishman was an extraordinary feat:
The [Norwegian] king had three sons: Amlaib, Imar, and Óisle. Óisle was the least of them in age, but he was the greatest in valor, for he outshone the Irish in casting javelins and in strength with spears. He outshone the Norwegians in strength with swords and in shooting arrows.
Literary depictions of battle give the impression that javelins were used in two distinct ways: the first is their use in an apparently formulaic 'phase of battle' style of combat; the annals imply that armies traded showers of arrows, then javelins and finally throwing spears before actually charging each other and engaging in hand-to-hand combat. However, it appears that some throwing weapons were saved for the actual melee, as we have descriptions of individuals killing notable enemies in the thick of battle with a javelin throw. For example, in the year 870, the Fragmentary Annals describes an account of the king of the Laigin taking out his enemy's body guard with a well-aimed javelin shot in the midst of the tumult and slaughter of battle. Another entry from 867 describes the assassination of a Norwegian noble named Háimar by an anonymous Munsterman who was "strong and hard and clever in the use of weapons" with a javelin, however the context of this entry isn't really clear and I'm not sure if the Norwegian was stabbed up close or killed by a thrown javelin.
So, these descriptions indicate that javelins and throwing-spears were an essential part of an early medieval Irish warrior's kit, that the Irish were seen as particularly adept at throwing spears and wielding them in battle, and that throwing weapons were used in routine-before melee volleys and as precision weapons meant to take out notable enemies in the chaos of the melee.
Not the 8th Century, but the poem "The Battle of Maldon" is 10th Century and says:
Hi leton þa of folman feolhearde speru, gegrundene garas fleogan;
or in Douglas B. Killings' translation:
They then sent forth from their hands shafts hard as file, murderously sharpened spears flew.
The spear is the most important weapon of the period, and came in a variety of forms. Light throwing spears (daroð, or "darts") were widely used before battle lines closed, partly to directly cause injury to lightly armoured opponents but also to interfere with an armoured opponent's shield. A spear embedded in a shield would render it difficult or impossible to use effectively.
The heavier javelin associated with earlier periods, the "angon" was apparently becoming less used by the 8th century. Thompson (see below) relates this to the use of less armour, and notes the expense of the heavier spear.
This is an excellent and well referenced article on the subject by Andrew Thompson.