glsl-inject-defines is a JavaScript utility for safely injecting `#define` statements into GLSL shader source code, ensuring they are placed after any `#version` or `#extension` directives. It is designed for developers working with WebGL or GLSL shaders who need to dynamically modify shader behavior at runtime, such as toggling features or injecting constants. The tool is particularly useful for projects using Node.js or browserify, and integrates seamlessly with glslify.