#Credentials to connect to office 365 site collection url
$url ="https://XXXXX/sites/MainSite/"
$userName ="XXXXXXXX.com"
$password ="XXXXXXX"

Write-Host "Loading libraries"
Add-Type -Path (Resolve-Path "$env:CommonProgram FilesCommon FilesMicrosoft SharedWeb Server Extensions16ISAPIMicrosoft.SharePoint.Client.dll")
Add-Type -Path (Resolve-Path "$env:CommonProgram FilesCommon FilesMicrosoft SharedWeb Server Extensions16ISAPIMicrosoft.SharePoint.Client.Runtime.dll")


Write-Host "Authenticating to SharePoint Online Tenant site $url"
$Context = New-Object Microsoft.SharePoint.Client.ClientContext($url)
#Credentials for the CSOM calls
$pass =  convertto-securestring $password -asplaintext -force
$credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($username, $pass)
$Context.Credentials = $credentials
$Context.RequestTimeOut = 5000 * 60 * 10;

$site = $context.Site
$web = $site.RootWeb
$Context.Load($web)
$Context.Load($site)
$Context.ExecuteQuery()

#Credentials for the Connect-SPOnline command
$cred = New-Object -TypeName System.Management.Automation.PSCredential -argumentlist $username, $(convertto-securestring $password -asplaintext -force)
Connect-SPOnline $web.Url -Credential $cred
Add-SPOJavaScriptLink -Name HomeLink -Url "XXXXXXXX/sites/MainSite/Style%20Library/myjavascript.js" –Scope Site


$Context.ExecuteQuery()