Using proj4js's "plugin" interface

const proj4 = require("proj4") const prcoords = require("prcoords") const noop = Function.prototype const DEG = Math.PI / 180 function xy_to_ll(p) { return { lon: p.x / DEG, lat: p.y / DEG } } function ll_to_xy(p) { return { x: p.lon * DEG, y: p.lat * DEG } } function xy_rename_ll(p) { return { lon: p.x, lat: p.y } } function ll_rename_xy(p) { return { x: p.lon, y: p.lat } } function wrap(f, ...args) { return (p) => ll_to_xy(f(xy_to_ll(p), ...args)) } // We lie our way to Baidu "Mercator". proj4.defs([ [ "_CLARK_MC", "+proj=merc +a=6378206.4 +b=6356583.8 +lat_ts=0.0 +lon_0=0.0 +x_0=0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs", ], ["_CLARK_LL", "+proj=longlat +a=6378206.4 +b=6356583.8"], ]) proj4.Proj.projections.add({ init: noop, forward: wrap(prcoords.wgs_gcj), inverse: wrap(prcoords.gcj_wgs_bored), names: ["gcj", "gcj02", "CN_Obfs_GCJ_2002_Ellipsoidal"], }) proj4.Proj.projections.add({ init: noop, forward: wrap(prcoords.wgs_bd), inverse: wrap(prcoords.bd_wgs_bored), names: ["baidu", "bd09", "CN_Obfs_Baidu_2009_Ellipsoidal"], }) proj4.Proj.projections.add({ init: noop, forward: (p) => proj4("_CLARK_LL", "_CLARK_MC", ll_rename_xy(prcoords.wgs_bd(xy_to_ll(p)))), inverse: (p) => ll_to_xy( prcoords.bd_wgs_bored(xy_rename_ll(proj4("_CLARK_MC", "_CLARK_LL", p))), ), names: ["baidumc", "bd09mc", "CN_Obfs_Baidu_2009_Mercator"], }) proj4.defs([ // Why isn't units=degrees working... work around with wrap() now. ["GCJ02", "+title=GCJ 02 (long/lat) +proj=gcj02 +units=degrees"], ["BD09", "+title=Baidu 2009 (long/lat) +proj=bd09 +units=degrees"], ["BD09MC", "+title=Baidu 2009 (Mercator) +proj=bd09mc +units=m"], ]) console.log([ // should be the same as https://artoria2e5.github.io/PRCoords/demo xy_to_ll(proj4("WGS84", "BD09", { x: 105, y: 35 })), xy_to_ll(proj4("WGS84", "GCJ02", { x: 105, y: 35 })), ]) console.log([ // should be very close to the original proj4( "BD09", "WGS84", ll_to_xy({ lat: 35.005403668456964, lon: 105.00966682831948 }), ), proj4( "GCJ02", "WGS84", ll_to_xy({ lat: 34.99909863223526, lon: 105.00328624145706 }), ), ]) console.log([ proj4("WGS84", "BD09MC", { x: 105, y: 35 }), proj4("BD09MC", "WGS84", { x: 11689750, y: 4139877 }), ])