Unused JavaScript
Browsers download, parse and execute all JavaScript sent to the page, even code that is never used. This check measures the potential saving…
Analyse my site for freeHow TheSiteFuse checks "Unused JavaScript"
Browsers download, parse and execute all JavaScript sent to the page, even code that is never used. This check measures the potential savings if unused JavaScript were removed. It's often caused by libraries imported in full when only a fraction of their functions are used (e.g. importing all of lodash just for _.debounce).
Real-world impact of "Unused JavaScript"
Every KB of unused JavaScript consumes bandwidth, download time and CPU parse time. On mobile, parsing 100 KB of JS can take 200–300 ms. It's one of the most frequent causes of slow pages according to PageSpeed analysis.
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