当对象非常多并且试图在范围内访问它时，为什么会出现“无法读取未定义的属性0”的信息？

Question

I have a function like

(function next(index) {

  var someObject = { 0:{some:"one"}, 1:{thing:"none"}, 2:{seconds: 5} };

  setTimeout(function() {
    //code ...
  }, (someObject[0][seconds]*1000) );

)(0);

And I am getting the following error in the second last line

myscript.js:7 Uncaught TypeError: Cannot read property '0' of undefined

It seems to be a scope problem, because I tried to access the 0th key like someObject[0] as well as someObject.0 but no luck.

But according to my understanding, someObject is defined in the same scope as the call to setTimeout() . So why am I getting this error. How co I fix this?

Answer 1

When you access [seconds] using bracket notation, it attempts to evaluate the variable seconds and uses that result to determine the property to access. Specify it in string format ['seconds'] or use period notation as noted here:

 var someObject = { 0:{some:"one"}, 1:{thing:"none"}, 2:{seconds: 5} }; try { console.log(someObject[2][seconds]*1000); } catch (e) { console.log(e.message); } console.log(someObject[2].seconds*1000); 

Additionally: someObject[0] is {some: "one"} which doesn't have any seconds parameter on it. I suspect you were trying to demonstrate someObject[2] instead.