javascript - 更改 js 函数的定义在某些浏览器中不起作用

Question

我搜索了这个问题的答案，但没有找到任何东西，尽管必须有一个简单的解释。下面的函数js在不同的浏览器中显示不同的结果...有人能告诉我为什么吗？非常感谢

var i='a';

if (i=='a')  function theFunction(){alert('hi');}
else         function theFunction(){alert('bye');};

theFunction();

//ff results in hi
//ie results in bye
//chrome results in bye

Answer 1

问题在于您在 if block 内使用了函数声明。

来自ECMA-262 :

NOTE Several widely used implementations of ECMAScript are known to support the use of FunctionDeclaration as a Statement. However there are significant and irreconcilable variations among the implementations in the semantics applied to such FunctionDeclarations. Because of these irreconcilable differences, the use of a FunctionDeclaration as a Statement results in code that is not reliably portable among implementations. It is recommended that ECMAScript implementations either disallow this usage of FunctionDeclaration or issue a warning when such a usage is encountered. Future editions of ECMAScript may define alternative portable means for declaring functions in a Statement context.

如果您尝试在严格模式下使用代码，您会得到

SyntaxError: in strict mode code, functions may be declared only at top level or immediately within another function

相反，您可以使用

var i='a',
    theFunction;

if (i=='a')  theFunction = function(){alert('hi');}
else         theFunction = function(){alert('bye');};
theFunction();

或者，如果您的代码足够简单(如上面的示例)，请使用三元运算符:

var theFunction = i=='a'
    ? function(){alert('hi');}
    : function(){alert('bye');};