The Makefile I'm using to compile .less file changes *when* the changes occur. Full write up: https://remysharp.com/makefile

Makefile

# when you run `make` alone, run the `css` rule (at the
# bottom of this makefile)
all: css

# .PHONY is a special command, that allows you not to
# require physical files as the target (allowing us to
# use the `all` rule as the default target).
.PHONY: all

# replace all .less files with .css extension and cache
# the results in a variable called `css_files`
css_files := $(patsubst %.less, %.css, $(wildcard ./public/css/*.less))

# when a .css file is *not* up to date compared to the
# .less file, then make will run the the following commands:
# - echo the string "foo.less -> foo.css"
# - run the command `lessc -x --source-map foo.less foo.css`
./public/css/%.css: public/css/%.less
  @echo "$< -> $@"
  @./node_modules/.bin/lessc -x --source-map $< $@

css: $(css_files)

package.json

{
  "name": "example app",
  "scripts": {
    "//": "I'm using `make` first, then running fswatch to pick up any changes up front",
    "watch": "nodemon -q -w public/css -e less -x make"
  }
}