javascript string in list returns false

Question

My site just started returning false for the following javascript check. I am trying to understand why.

_test = ["0e52a313167fecc07c9507fcf7257f79"]
"0e52a313167fecc07c9507fcf7257f79" in _test
>>> false
_test[0] === "0e52a313167fecc07c9507fcf7257f79"
>>> true 

Can someone help me understand why ?

Answer 1

the in operator tests if a property is in an object. For example

var test = {
    a: 1,
    b: 2 
};

"a" in test == true;
"c" in test == false;

You want to test if an array contains a specific object. You should use the Array#indexOf method.

test.indexOf("0e52...") != -1 // -1 means "not found", anything else simply indicates the index of the object in the array.

Array#indexOf at MDN: https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Array/indexOf

Answer 2

From the MDN :

The in operator returns true if the specified property is in the specified object.

It checks the key, not the value.

There, the property key would be 0, not "0e52a313167fecc07c9507fcf7257f79".

You can test that 0 in _test is true.

If you want to check if a value is in an array, use indexOf :

_test.indexOf("0e52a313167fecc07c9507fcf7257f79")!==-1

(a shim given by the MDN is necessary for IE8)