Does lifelink from a spell or ability work the same way as lifelink from a static ability?

Lifelink as a keyword ability (a static ability printed on or granted to a permanent) works via a continuous effect: whenever that source deals damage, its controller gains that much life simultaneously, as a consequence of the damage event itself (CR 702.15b). This is not a triggered ability — it happens as part of damage being dealt, before any player receives priority.

Lifelink granted by a spell or activated/triggered ability — for example, an effect that says 'target creature gains lifelink until end of turn' — also functions as a static ability granting the keyword, so it actually works identically to printed lifelink once the effect resolves and the creature has the keyword. The life gain still happens as damage is dealt, not after the fact.

The key distinction that used to matter (before the 2010 rules update) no longer applies. In the current rules, all forms of lifelink — printed, granted by auras, granted by instants/sorceries — are the same static keyword and function identically under CR 702.15. There is no 'triggered' version of lifelink in the current rules.

Concrete example: You cast Giant Growth on your 2/2, giving it +3/+3 and lifelink until end of turn. When it deals 5 combat damage, you gain 5 life simultaneously with that damage being dealt — not after the damage step ends. This behaves exactly the same as if the creature had lifelink printed on it.

So the answer is: in the current rules, lifelink from any source (static keyword, aura, or instant grant) works the same way — life is gained as damage is dealt (CR 702.15b, 119.3f).