cesium npm installation failed because of fetch step failure.

I am trying installing cesium-1.4.9 on my computer which runs win7. But I have a troule here: npm ERR! Invalid response while trying to fetch https://registry.npmjs.org/js-tokens: Integrity verification failed for........
I don't know why.

Can you post the full error? It sounds like it might be an npm issue. Check out some of the solutions here: