Scoping

not able to understand why 'a' is undefined

let a = 'hello'; // globally scoped
var b = 'world'; // globally scoped
console.log(window.a); // undefined
console.log(window.b); // 'world'

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well explanation

wherever i touch the video it's going to pause the video. it's so difficult to see videos in phone. may be it's like a YouTube control i will like it.