Javascript function-level scope [closed]

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This is just a curiosity. But It is something that i would like to know.

I know that Javascript 1.7 support block scoping with let keyword.

But Why Javascript has been initially desinged with function-level scope instead of block scope?

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A reasonable guess (but only a guess) could be that the very earliest iterations of the language did not have a var keyword but depended on a variable implicitly being created when it was assigned to. This is quite common for simple scripting languages -- many of them have to retrofit some explicit declaration mechanism as they mature and begin being used for large projects. Under this assumption, in order for code such as

if( bla bla bla ) {
  a = 24 ;
} else {
  a = blop.blop();
}
alert(a);

it wouldn't do if the implicit declarations of a were to be trapped by the braces instead of being visible at the alert. Thus, function-level scope.

Now imagine that by the time var was added, the assumption of function-level scope had already become entrenched in the specification and implementation of the language ...