To install the script you need a project so make sure you have created one. If you haven’t, you can create one here. Once you have your project, click on the Settings icon -> Setup instructions and add the domain name where you wish to install the script. Copy the Public API key form that window and paste it in the script below by replacing <project-public-api-key> with it. 
<script src="https://cdn.visitorquery.com/visitorquery.js"></script>
<script type="text/javascript">
	window.addEventListener('load', () => {
		window.VisitorQuery.run({
			ApiKey   : "<project-public-api-key>",
			SessionId: "session-id-of-the-user"
		});
	});
</script>
Keep in mind that, for security reasons, a Public API key will only work when the request originates from the domain that you have added in the project settings.

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The session id

We recommend using a unique session id for each user session. This can be a random string or a unique identifier that you generate. The session should not be long lived, this is not something like a cookie that you store for a long time. It should change if the user closes the tab/window. Failing to do so could lead to a lot of fals positives when checking the session data due to pollution from other sessions of the same user.

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Install complete

Once you have installed the script, you can create a pageview on your website and the results should start showing in the project’s page in the dashboard. To programatically check a user’s session data, use our REST APIs.