了解 Javascript Object 和未定义

Question

I am trying to fix a Wordpress plugin that is no longer supported. I have narrowed down the error. The following line is the problem:

i[C][0];

It is returning undefined in the function below:

`function S(i) {
        var C,
            P = i.length,
            E = [];
            
      for (C = 0; C < P; C++) {
      console.log(i[C]);
      console.log( JSON.stringify(i[C], null, 2) ); 
      E[C] = i[C][0].offsetTop;
      }
        return E;
    }`

I logged i[C] and have the following result:

"length": 0, "prevObject": { "0": {}, "length": 1, "prevObject": { "0": {}, "1": {}, "2": {}, "3": {}, "4": {}, "5": { "jQuery351075030630793491351": { "display": "" } }, "length": 6, "prevObject": { "0": {}, "length": 1, "prevObject": { "0": {}, "length": 1, "prevObject": { "0": {}, "length": 1 } } } } } }

Here is a link to the page: https://wolseleyfamilyplace.com/events/

Another note, P is equal to 5.

I am not that familiar with Javascript and reading the objects. Why is the i[C][0] returning undefined? Can it be fixed?

Answer 1

Maybe it was expecting i to be a jQuery object... And now what is passed to the function is a DOM element.

Try to just remove [0] from E[C] = i[C][0].offsetTop; It all works fine, that was it!

---

To just be fullproof... In case both DOM and jQuery object can be passed to the function, you could do:

E[C] = i[C][0]? i[C][0].offsetTop: i[C].offsetTop
jQuery--^ DOM--^