Declarative styles such as functional programming (FP) are rapidly gaining ground on their imperative cousins, including procedural and object-oriented programming. The shift is subtle because it is happening within the context of multiparadigm programming languages such as JavaScript. FP is better suited to modern processes like test-driven development (TDD), and architectures like massively parallel, cloud-based computing. This article describes the technical details that characterize the shift from imperative to FP and implications for software quality management, particularly reuse and testability.