javascript - 以下语法有什么区别？

Question

1. $(function () {
       function foo() { return true; }
       log(bar());                        // getting error
       var bar = function() { return true; };   
  });

2. $(function () {
       function foo() { return true; }
       var bar = function() { return true; };
       log(bar());                        // Working   
  });

我的困惑是以下两个声明之间有什么区别，哪个有用？

var bar = function() { return true; };

function bar(){ return true; };

Answer 1

The:

function bar(){ return true; };

is function declaration which is hoisted to top by the interpreter, you can call from any place, while:

var bar = function() { return true; };

is function expression you can call only after it is defined. It won't be available before or up in the code just like you were doing:

log(bar());                        // getting error
var bar = function() { return true; }; 

Getting error because on first line bar isn't available yet. To solve that, use function declaration instead if you want.

---

To learn more about the difference between function declaration and function expression, I highly recommend you to read this great article by Kangax:

• Named function expressions demystified

Answer 2

Sarfraz 已经得到了很好的解释。我只是想添加更多，第一个功能，

var bar = function(){ return true; };

更灵活，您可以在声明后添加更多属性或方法：

bar.anotherMethod = function() { alert("This is another method"); }
bar.anotherProperty = 'some value';

虽然function bar(){ return true; }不能那样做。`