怪异的编程问题(希望大家补充)

怪异的编程问题

(1)JavaScript中的作用域

var jsFuture = "es6";
(function () {
  if (!jsFuture) { var jsFuture = "es5"; }
  console.log(jsFuture);
}());

 实际输入结果是:es5,而不是es6

原因:变量声明将被提升到最上面.

(2)

var es = [];
for (var i = 0; i < 10; i++) {
  es[i] = function () {
    console.log("Upcoming edition of ECMAScript is ES" + i);
  };
}
es[6](); // Upcoming edition of ECMAScript is ES10

 Notice that, even though var i = 0; is declared in the for loop, the scope ofvar i defaults to global. Hence, when the function es[6]() is executed, the value of i is 10.

(3)