初学者javascript; 带有未定义对象列的for循环

Question

Here is my code

function Person (name, age) {
this.name = name;
this.age = age;
}

var family = new Array();
family[0] = new Person("alice", 40);
family[1] = new Person("bob", 42);
family[2] = new Person("michelle", 8);
family[3] = new Person("timmy", 6);

for (i =0; i<= family.length; i++) {
    console.log (family[i].name);
}

This produces an error: TypeError: Cannot read property 'name' of undefined

Can anyone point me in the right direction from here?

Answer 1

You're iterating one too far.

for (var i = 0; i < family.length; i++)

JavaScript arrays start at zero, and the last non-empty cell is at length - 1 . Thus you have to stop iterating when your index is equal to the length, not when it's greater than the length.

Answer 2

您应该将测试条件更改为i < family.length ，您将越界。

Answer 3

那i < family.length呢？

Answer 4

Change <= to <. You are exceeding the array limit.

Answer 5

It works just fine.

for (i =0; i<= family.length; i++)

demo: http://jsfiddle.net/285Th/1/