Why is there C in my javascript?!

c_in.js

/* from http://madebyevan.com/webgl-water/water.js
   used in the awesome WebGL water demo
   http://madebyevan.com/webgl-water/*/
   
  this.dropShader = new GL.Shader(vertexShader, '\
    const float PI = 3.141592653589793;\
    uniform sampler2D texture;\
    uniform vec2 center;\
    uniform float radius;\
    uniform float strength;\
    varying vec2 coord;\
    void main() {\
      /* get vertex info */\
      vec4 info = texture2D(texture, coord);\
      \
      /* add the drop to the height */\
      float drop = max(0.0, 1.0 - length(center * 0.5 + 0.5 - coord) / radius);\
      drop = 0.5 - cos(drop * PI) * 0.5;\
      info.r += drop * strength;\
      \
      gl_FragColor = info;\
    }\
  ');