A sample LaunchAgent for zedd, with node installed through MacPorts. Change the path of node and of zedd to fit your installation.

org.zedapp.zedd.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
    <dict>
        <key>Label</key>
            <string>org.zedapp.zedd</string>
        <key>ProgramArguments</key>
            <array>
                <string>/opt/local/bin/node</string>
                <string>/opt/local/bin/zedd</string>
            </array>
        <key>RunAtLoad</key>
            <true/> 
    </dict>
</plist>