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I read that the javascript language provides a simple non-blocking IO mechanism which contributes to the success of projects like node.js. My question is how does non-blocking IO work in javascript and why is it trickier to implement in other languages?

I read that the javascript language has characteristics that assist in the implementation of non-blocking IO which contributes to the success of projects like node.js. My question is what are these characteristics and why is non-blocking IO trickier to implement in other languages?