Javert swears, upon the stars, that he will never rest until he hunts down Jean Valjean. Through the song Stars, we get an economic lesson on elasticity and inelastic demand. Elasticity of demand refers to how sensitive someone's preferences are to changes in price. If someone is sensitive to price changes, their demand is elastic (responsive), and they might change their purchasing behavior when prices change.
Through the song, we learn that Javert has an inelastic demand for hunting Jean Valjean.
As we see in the video, which contains the full song and and deeper analysis, Javert swears that he will devote his entire life, regardless of the cost, to hunt down Valjean. That means his preferences are perfectly inelastic.