If-statement fail in javascript

Question

For several hours now am I trying to make a simple game, but one if-statement is failing:

function checkDiagonaal() {
    if (document.getElementById("11").src.indexOf("o.png") &&
        document.getElementById("22").src.indexOf("x.png") &&
        document.getElementById("33").src.indexOf("o.png"))
    {
        winnaar = true;
    }
}

The condition is not true, yet the variable winnaar is set on true . I don't see what I am doing wrong. Very probably just a little mistake.

I also tried this code:

if(document.getElementById("11").src === "images/o.png") 

but this returns false (even when the condition is true). I would like to know why?

Answer 1

在这种情况下使用...indexOf(...) >= 0 。

Answer 2

当找不到值时，indexOf返回-1，-1是真的

Answer 3

From the MDN (great resource!):

"The indexOf() method returns the index within the calling String object of the first occurrence of the specified value [...] returns -1 if the value is not found."

When statements get big they become a bit unreadable, it might be fine now, but if you need to add more checks, I would suggest a different approach:

function checkDiagonaal() {
  var ids = [11,22,33];
  var strs = ['o.png','x.png','o.png'];
  var winnar = ids.every(function(id,i) {
    return document.getElementById(id).src.indexOf(strs[i]) > -1;
  });
}