官方標準安裝方法：

$ brew tap dart-lang/dart
$ brew install dart

但是執行第二步會出錯：

==> Installing dart from dart-lang/dart
==> Downloading https://storage.googleapis.com/dart-archive/channels/stable/release/2.0.0/sdk/dartsdk-macos-x64-release.zip

curl: (35) LibreSSL SSL_connect: SSL_ERROR_SYSCALL in connection to storage.googleapis.com:443
Error: An exception occurred within a child process:
DownloadError: Failed to download resource "dart"
Download failed:

原因可能是牆，也可能是伺服器問題。單獨下載https://storage.googleapis.com/dart-archive/channels/stable/release/2.0.0/sdk/dartsdk-macos-x64-release.zip
幾乎走不動。
從這兒下載：
https://download.csdn.net/download/dreamfine/10734968
然後解壓就行了，隨便你放在哪兒，在Dart IDE，如webstorm中, 指定SDk位置就行了。