Javascript String Compare == sometimes fails

How could the following code sometimes evaluate to false?

(transport.responseText == '1' || 
 transport.responseText == 'CARD_VALID')

My JavaScript code:

if (transport.responseText == '1' || 
    transport.responseText == 'CARD_VALID') {
    // do something.
}
else if (transport.responseText == 'CARD_INVALID' || 
             transport.responseText == 'INVALID_CHECKSUM') {
    // do something else....
}
else {
    new Ajax.Request('/report_error.php?responseText='+transport.responseText);
    // report error to user
}

What could cause JavaScript string compare == to return false when the strings are identical?

Solution 1:

Double equals is the appropriate way to compare strings in Javascript, it is returning false then there may be whitespace to the left and or right of one string.

Put a .trim() on the end of the strings and my comparison should started working:

var panel = response.substr(0, response.indexOf("<")).trim();
if(panel == "combo"){
    //do something
}

Solution 2:

I had a similar problem where two obviously identical strings would not be equal, and I was pulling my hair out trying to solve it, so I did this:

for (var c=0; c<string_1.length; c++) {
    if (string_1.charCodeAt(c) != string_2.charCodeAt(c)) {
        alert('c:'+c+' '+string_1.charCodeAt(c)+'!='+string_2.charCodeAt(c));
        valid = false;
    }
}

And I found that the last character on one string was 10, and the last character on the other was 13, I thought both strings were null terminated, but they were not.

Solution 3:

A1 = "speed"
A2 = "speed" 

if(A1 == A2)  => Error !!!

USE THIS TEST IN CONSOLE:

escape("speed")

result: "speed"

escape(A1)

result: "speed%0D" => This is the problem %0D !!!

escape(A2)

result: "speed" => OK !!!

Use correct code:

if(A1.slice(0, -1) == A2) This is OK!