block a block, also known as a compound statement, is defined by curly braces {}. it groups multiple javascript statements together into a single unit. { //compound statement var x = 60; ...
块作用域指在大括号内声明的变量和函数仅在该块内可访问。var 属于函数或全局作用域,而 let 和 const 属于块作用域。相同名称的变量会发生遮蔽,let 和 const 不能被 var 遮蔽。