Option One: make

One way of scripting mapshaper is to call the mapshaper command line program from make or other build tool.
If you include mapshaper as a dependency in the package.json file of a Node.js project, the executable programs mapshaper and mapshaper-xl can be found in node_modules/.bin/ and node_modules/mapshaper/bin/.
Here's an example Makefile target:

                europe.json: shp/europe.shp
                    mapshaper snap $ encoding=utf8  \
                    -rename-layers countries \
                    -filter "CONTINENT == 'Europe'" \
                    -simplify 15% keep-shapes \
                    -o format=topojson $@
                
            

Option Two: Node API

Mapshaper has three API functions for running editing commands: runCommands(), applyCommands() and runCommandsXL(). All three functions take a commands option, which is a string containing the same command line options that are passed to the mapshaper command line program.

runCommands()

runCommands(commands[, input][, callback])
commands A command line string containing mapshaper commands (typically starting with -i and ending with -o).
input An optional JS object containing contents of files referenced by -i command(s), indexed by file name. Input files are read from the filesystem if they are not present in the input argument.
callback An optional Node-style callback: function(Error). If called without a callback, runCommands() returns a Promise.

                // Example: converting a directory of Shapefiles to GeoJSON

                    var mapshaper = require('mapshaper');

                    mapshaper.runCommands('-i shapefiles/*.shp -o geojson/ format=geojson');
                
            

applyCommands()

runCommands(commands[, input][, callback])
This function has the same signature as runCommands(). Instead of writing files generated by the -o command, mapshaper sends the output file contents to a callback (or Promise if a callback is not provided). File data is placed in a JavaScript object and indexed by filename.

                // Example: converting a CSV string to GeoJSON

                    const input = {'input.csv': 'lat,lng,value\n40.3,-72.3,1000'};

                    const cmd = '-i input.csv -points x=lng y=lat -o output.geojson';


                    
                    // using callback

                    mapshaper.applyCommands(cmd, input, function(err, output) {

                        // do something with {"output.geojson": [Buffer]}

                    });


                    
                    // using Promise

                    const output = await mapshaper.applyCommands(cmd, input);
                
            

runCommandsXL()

runCommands(commands[, input][, callback])
This function runs commands in a sub-process that has a larger maximum heap size than Node's default.
Calling this function is equivalent to running the mapshaper-xl command line program. You can override
the default 8gb amount by passing an options object, like this: {xl: "16gb"}.
This function only takes input from the filesystem; unlike runCommands(), there is no input option.

Note on Shapefile input

To input a Shapefile using applyCommands() or runCommands(), in addition to passing the contents of the .shp file (as a Buffer or ArrayBuffer), you'll probably want to pass the .dbf file (as a Buffer or ArrayBuffer) and the .prj file (as a string). The .dbf file contains attribute data and the .prj file contains coordinate system data.