# CustomFit JS Script

**What are the different modes to configure the CustomFit's client SDK (java-script)?**�

CustomFit provides 2 modes

1. **Classic (Sync) mode**: When the webpage loads, it will be hidden, and after fetching and applying the personalized content changes, the webpage will be made visible.
2. **Intelligent (Async, preferred one)**: When the web page loads, it first intelligently hides only those elements that are personalized and page load won't be blocked. And after fetching the personalized changes are applied those elements will be made visible.

**Why the CustomFit \<script> needs to be added without async or deferred attribute?** �

Typically for any personalization or A/B test platforms, the script has to be sync, because the content changes need to be applied before the page is visible, else it will result in flickering (the visitors see the old content getting replaced by the new content)

But CustomFit's intelligent mode won't block the page loading after the script has been downloaded as all the fetching & applying of the personalized content changes happens in async mode.

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