* Install latest [emsdk](https://kripken.github.io/emscripten-site/docs/getting_started/downloads.html). Do not use system-provided `emscripten` package, because it contains too old version.
* Install all `TDLib` build dependencies as described in [Building](https://github.com/tdlib/td#building).
* Run `source ./emsdk_env.sh` from `emsdk` directory to set up correct build environment.
* On `macOS` install `coreutils` [Homebrew](https://brew.sh) package and replace `realpath` usages in scripts with `grealpath`:
```
brew install coreutils
sed -i.bak 's/[(]realpath/(grealpath/g' build-tdlib.sh