Error reporting after plug-in introduction

TypeError: fs.readFileSync is not a function
at Module.eval (webpack-internal:///./node_modules/@mapbox/mapbox-gl-directions/src/controls/inputs.js:16)
at eval (webpack-internal:///./node_modules/@mapbox/mapbox-gl-directions/src/controls/inputs.js:162)
at Module../node_modules/@mapbox/mapbox-gl-directions/src/controls/inputs.js (0.js:47)
at __webpack_require__ (app.js:767)
at fn (app.js:130)
at eval (webpack-internal:///./node_modules/@mapbox/mapbox-gl-directions/src/directions.js:11)
at Module../node_modules/@mapbox/mapbox-gl-directions/src/directions.js (0.js:71)
at __webpack_require__ (app.js:767)
at fn (app.js:130)
at Module.eval (webpack-internal:///./node_modules/@mapbox/mapbox-gl-directions/src/index.js:2)

Start by reproducing the reported TypeError from the webpack stack trace, then inspect node_modules/@mapbox/mapbox-gl-directions/src/controls/inputs.js and its callers in src/directions.js and src/index.js. Done means the plug-in loads without the fs.readFileSync error in the reported webpack context; the issue does not name a test or a more specific expected change.

Written by the indexing model from the issue text.