javascript - if(xxx || xxx), what am I doing wrong? - Stack Overflow

Can someone explain to me what am I doing wrong?

function navMenuIntervalCheck() {
    if (currentSiteUrl != "subsites/players.php" || currentSiteUrl != "subsites/itemshop.php") {
        $.ajax({
            url: currentSiteUrl,
            cache: false,
            success: function (dataForContainer) {
                $('#container').html(dataForContainer);
            }
        });
    }

    screenControlCheck();
};

setInterval(function () {
    navMenuIntervalCheck()
}, 5000);

When I run my website it refreshes even when currentSiteUrl==subsites/players.php

Can someone explain to me what am I doing wrong?

function navMenuIntervalCheck() {
    if (currentSiteUrl != "subsites/players.php" || currentSiteUrl != "subsites/itemshop.php") {
        $.ajax({
            url: currentSiteUrl,
            cache: false,
            success: function (dataForContainer) {
                $('#container').html(dataForContainer);
            }
        });
    }

    screenControlCheck();
};

setInterval(function () {
    navMenuIntervalCheck()
}, 5000);

When I run my website it refreshes even when currentSiteUrl==subsites/players.php

• javascript
• if-statement

Share Improve this question Follow edited Apr 9, 2013 at 20:36 Nope 22.3k88 gold badges4949 silver badges7373 bronze badges asked Apr 9, 2013 at 20:34 Kamil OczkowskiKamil Oczkowski 13522 silver badges1111 bronze badges 2

• Where do you assign currentSiteUrl? – Bart Commented Apr 9, 2013 at 20:36
• 1 && vs || ?, the second condition matches – David Commented Apr 9, 2013 at 20:36

Add a ment  | 

6 Answers 6

Sorted by: Reset to default 10

As x!='a' || x!='b' is always true, I guess you wanted && instead of ||.

Read || as OR and && as AND.

More details in the MDN on logical operators.

currentSiteUrl can only have one value, so it will always be that at least one of the values you're testing will not equal currentSiteUrl, making the if condition always true.

I think you meant to use && or you meant to do == with ||.

Your code says this :

Refresh when currentSiteUrl is different than subsites/players.php or different than subsites/itemshop.php.

So subsites/players.php is indeed different than subsites/itemshop.php

Use && instead of ||

Look at your if statement:

if (a != foo || a != bar)

Lets look at the possibilities:

• a = foo. This will evaluate as true, because a != bar
• a = bar. This will evaluate as true, because a != foo
• a = anything else. This will evaluate as true, because a != foo

Your if statement always evaluates to true.

As others have already said, you want to replace your || with &&.

Let me throw a logical rule at you, called DeMorgan's Law. It's really useful when learning how to set up a good if statement.

!(a || b) === !a && !b

also

!(a && b) === !a || !b

What that says is: "Not (one event or another)" is the same thing as "Not one event and not another", and "Not (one event and another)" is the same thing as "Not one event or not the other".

I know this has been answered but thought it might help to add some additional information using your own code.

As said, switching logical operator from || to && will work:

if (currentSiteUrl != "subsites/players.php" && currentSiteUrl != "subsites/itemshop.php")

But why is that?

---

Using ||

---

The || logical operator returns true if either the first or second expression is true and only if both are false will it return false.

Hence:

• if currentSiteUrl != "subsites/players.php" is true you end up in the if block

• if currentSiteUrl != "subsites/players.php" is false and currentSiteUrl != "subsites/itemshop.php" is true you end up in the if block

There will never be another scenario as your variable currentSiteUrl can only hold a single value and as such one of the expressions will always be true causing you to always end up in the if block.

---

Using &&

---

Using the && logical operator on the other hand though returns false if either the first or second expression is false and only if both are true will it return true.

Hence:

• if currentSiteUrl != "subsites/players.php" is true and currentSiteUrl != "subsites/itemshop.php" is true you end up in the if block

• if currentSiteUrl != "subsites/players.php" is true and currentSiteUrl != "subsites/itemshop.php" is false you don't end up in the if block

• if currentSiteUrl != "subsites/players.php" is false you don't end up in the if block

There will never be another scenario, because only if both expression are true will you end up in the if block and as soon as either expression is false will you not.

How are you getting the currentSiteUrl. A url is followed by protocol:://domain

Try using the follwoing property to get URL and then match it

window.location.href

This url will also include the http or https and domain name