proj4js/lib/common/adjust_lon.js

var TWO_PI = Math.PI * 2;
// SPI is slightly greater than Math.PI, so values that exceed the -180..180
// degree range by a tiny amount don't get wrapped. This prevents points that
// have drifted from their original location along the 180th meridian (due to
// floating point error) from changing their sign.
var SPI = 3.14159265359;
var sign = require('./sign');

module.exports = function(x) {
  return (Math.abs(x) <= SPI) ? x : (x - (sign(x) * TWO_PI));
};