JavaScript compare two strings with the same value fails

Question

I'm trying to compare two strings which seems containing the same value but it doesn't work.

here is my code:

ABC.prototype.is_in_DB = function () {
    var ans = "";
    if (window.XMLHttpRequest) {
        var xmlhttp = new XMLHttpRequest();
    } else {
        var xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
    }
    xmlhttp.onreadystatechange = function () {

        if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
            ans = (xmlhttp.responseText);
        }
        return ans;
    }
    xmlhttp.open("POST", "ABC_DB.php", false);
    xmlhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    xmlhttp.send("id=" + this.get_id() + "&name=" + this.get_type() + "&description=" + this.get_description() + "&kind=" + this.get_kind());

    var check = "true";

    console.log("this is ans type    " + typeof (ans));
    console.log("this is ans length    " + ans.length);
    console.log("this is ans     " + ans);
    console.log("this is check type    " + typeof (check));
    console.log("this is check length    " + check.length);
    console.log("this is check     " + check);

    if (ans === check) {
        console.log("the if is true ");
        return true;
    } else {
        console.log("the if is false ");
        return false;
    }
}

the php file works and it's end looks like this (there are no more echo commands in the file)

 if ($row_cnt>0){
     echo('true');
 } else {
     echo('false');
 }

when I'm printing the values of the strings i receive the following

this is ans type string

this is ans length 5

this is ans true

this is check type string

this is check length 4

this is check true

the if is false

Do you have any idea how I can compare it?

looks like ans contains some white space from response so use ans.trim() == check — Abhik Chakraborty
– Abhik Chakraborty, Commented Apr 4, 2014 at 20:34
Why are you doing synchronous ajax? Eeeck. Lock up the browser during the ajax call. — jfriend00
– jfriend00, Commented Apr 4, 2014 at 20:36

tf.alves · Accepted Answer · 2014-04-04 20:34:45Z

1

Try to do ans.trim() and using == instead of === It seems that ans could also have a trailing character like a \n

answered Apr 4, 2014 at 20:34

tf.alves

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NeoNexus DeMortis · Accepted Answer · 2014-04-04 20:34:15Z

0

Wild guess here, but because the length of "ans" is 5, but the value is "true", I'm willing to bet there is a space in there. Try adding trim(ans) before your echo's, and see if that fixes it.

answered Apr 4, 2014 at 20:34

NeoNexus DeMortis

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Buzinas · Accepted Answer · 2014-04-04 20:35:42Z

0

It seems your responseText is coming with some white spaces.

Try to use: if (ans.trim() == check)

answered Apr 4, 2014 at 20:35

Buzinas

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knightsb · Accepted Answer · 2014-04-04 20:36:45Z

0

try eliminate the possibility that ans and check are not the same object use == instead ===

answered Apr 4, 2014 at 20:36

knightsb

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liran · Accepted Answer · 2014-04-05 10:04:58Z

0

thanks to everybody. what i found that works for me was to add this two following line

x=(xmlhttp.responseText);
ans=x.replace(/^\s*/,'').replace(/\s*$/,'').toLowerCase();

the problem i faced was due to additional white spaces. this line eliminate them.

answered Apr 5, 2014 at 10:04

liran

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