函数声明和函数表达式

function foo(){

    function bar() {

        return 3;

    }

    return bar();

    function bar() {

        return 8;

    }

}

alert(foo());

 

题 2:

 

function foo(){

    var bar = function() {

        return 3;

    };

    return bar();

    var bar = function() {

        return 8;

    };

}

alert(foo());

 

题 3:

 

alert(foo());

function foo(){

    var bar = function() {

        return 3;

    };

    return bar();

    var bar = function() {

        return 8;

    };

}

 

题 4:

 

function foo(){

    return bar();

    var bar = function() {

        return 3;

    };

    var bar = function() {

        return 8;

    };

}

alert(foo());

 

答案是8、3、3和 [Type Error: bar is not a function]

 

分析：

//**Simulated processing sequence for Question 1**

function foo(){

    //define bar once

    function bar() {

        return 3;

    }

    //redefine it

    function bar() {

        return 8;

    }

    //return its invocation

    return bar(); //8

}

alert(foo());

 

return 语句后面的代码是运行不到的啊……

 

//**Simulated processing sequence for Question 2**

function foo(){

    //a declaration for each function expression

    var bar = undefined;

    var bar = undefined;

    //first Function Expression is executed

    bar = function() {

        return 3;

    };

    // Function created by first Function Expression is invoked

    return bar();

    // second Function Expression unreachable

}

alert(foo()); //3

 

 

//**Simulated processing sequence for Question 4**

function foo(){

    //a declaration for each function expression

    var bar = undefined;

    var bar = undefined;

    return bar(); //TypeError: "bar not defined"

    //neither Function Expression is reached

}

alert(foo());