We Should Stop Using JavaScript, According to Douglas Crockford
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Of course it could be another Silverlight in the making.
Silverlight required a plug-in. That's a barrier to adoption that they never overcame. When plugins were outlawed it was impossible to continue Silverlight. Microsoft had seen the writing on the wall and had effectively abandoned Silverligt as a strategic product long before that. Blazor Webassembly is not in the same situation. Webassembly is not going to be pulled. Webassembly is objectively better than Javascript for the task of running code in the browser, so my prediction is that Javascript will be deprecated before Webassembly.
JS has huge inertia and I think it will take some time to displace it, even with better options available.
The problems with JavaScript are with enormous complexity and churn within the prevailing frameworks of the ecosystem.