Javascript Tracking is used to signal events to a Tracking Service in the web environments where Javascript is enabled (which will happen in most cases — most users browsing the web on desktop or mobile will usually have Javascript enabled). In web environments where Javascript is disabled, tracking can usually still be accomplished by image trackers. In the in-app world, tracking is usually achieved through API tracking integrations.
Javascript tracking can be used to track any important web events: impression events (when ads are shown to a user), click events (when ads are clicked on, or when the user lands in one of the advertiser’s properties through an outbound link from an ad or a link from another site, a clickthru from an influencer mention or affiliate link, etc..) and conversion events (when the user makes a purchase, or completes a lead gen form, etc…). It can also measure other related metrics typically associated with web analytics, such as session-level duration, # of pageviews, etc…