Javascript array value is undefined … how do I test for that [duplicate]

Answer 1

try: typeof(predQuery[preId])=='undefined'
or more generally: typeof(yourArray[yourIndex])=='undefined'
You're comparing "undefined" to undefined, which returns false =)

Answer 2

There are more (many) ways to Rome:

//=>considering predQuery[preId] is undefined:
predQuery[preId] === undefined; //=> true
undefined === predQuery[preId] //=> true
predQuery[preId] || 'it\'s unbelievable!' //=> it's unbelievable
var isdef = predQuery[preId] ? predQuery[preId] : null //=> isdef = null

cheers!

Answer 3

This code works very well

function isUndefined(array, index) {
    return ((String(array[index]) == "undefined") ? "Yes" : "No");
}

Answer 4

predQuery[preId]=='undefined'

You're testing against the string 'undefined'; you've confused this test with the typeof test which would return a string. You probably mean to be testing against the special value undefined:

predQuery[preId]===undefined

Note the strict-equality operator to avoid the generally-unwanted match null==undefined.

However there are two ways you can get an undefined value: either preId isn't a member of predQuery, or it is a member but has a value set to the special undefined value. Often, you only want to check whether it's present or not; in that case the in operator is more appropriate:

!(preId in predQuery)

Answer 5

You are checking it the array index contains a string "undefined", you should either use the typeof operator:

typeof predQuery[preId] == 'undefined'

Or use the undefined global property:

predQuery[preId] === undefined

The first way is safer, because the undefined global property is writable, and it can be changed to any other value.

Answer 6

Check for

if (predQuery[preId] === undefined)

Use the strict equal to operator. See comparison operators