So this is just repeated throughout the song. I think its a nice bass line, even though 
it is simple. Love Lorde and this song. If there is anything wrong sorry this is my 
first tab

G|-----------------|
D|-----------------|  This is just played throughout the song so have fun!
A|-0---7---9---4---|
E|-----------------|

Can also be played like this but I personally prefer the other one when I play
G|-----------------|
D|-----2----4------|
A|-0-------------4-|
E|-----------------|

you can also just hold out these as strums, but I like to just beat them through the 
song when it gets stronger, but yeah up to you! Hope you enjoy!