Check if string is empty with jquery

Question

I am running a client side validation javascript which will submit a form via an ajax post after validating the data. Here is the javascript:

$(".button").click(function() {

            $(".error").hide();

            var name = $(":input.name").val();
            if ((name == "") || (name.length < 4)){

                $("label#nameErr").show();
                $(":input.name").focus();
                return false;
            }

            var email = $(":input.email").val();
            if (email == "") {

                $("label#emailErr").show();
                $(":input.email").focus();
                return false;
            }


            var phone = $(":input.phone").val();
            if (phone == "") {

                $("label#phoneErr").show();
                $(":input.phone").focus();
                return false;
            }

            var comment = $("#comments").val();
            if ((!comment) || (comment > 100)) {

                $("label#commentErr").show();
                $("#comments").focus();
                alert("hello");
                return false;
            }

            var info = 'name:' + name + '&email:' + email + '&phone:' + phone + '&comment:' + comment;
            var ajaxurl = '<?php echo admin_url("admin-ajax.php"); ?>';
            alert(info);

            jQuery.ajax({

                type:"post",
                dataType:"json",
                url: myAjax.ajaxurl,
                data: {action: 'submit_data', info: info},
                success: function(response) {
                    if (response.type == "success") {

                        alert("success");
                    }
                    else {

                        alert("fail");
                    }
                }
            });

            $(":input").val('');
            return false;


        });

The four input fields are three text inputs for name, email and phone and then one textarea for the comments/queries section. The problem is that if I leave the textarea blank or enter over 100 characters the script does not go into the if ((!comment) || (comment > 100)) statement. I am wondering if there is a different value that gets assigned to a textarea when it is blank that is stopping the code from seeing it as empty ?

Hello! Don't forget to accept an answer - you even get 2 rep for it! — SomeKittens
– SomeKittens, Commented Apr 3, 2014 at 22:34

SomeKittens · Accepted Answer · 2014-04-03 21:57:33Z

24

You need to check the length property of comment (also, you have a few extra parens. They won't break anything, but aren't needed).

if (!comment || comment.length > 100) {

What's currently happening is that you're trying to determine if a given string is less than a number, which is quite silly, so JS declares it false. Checking comment.length compares it to a number, which is what you wanted it to do.

!comment works because an empty string is falsy, though what you think is empty might not be (for instance, a string with a space is non-empty: ' '). Use .trim() to eliminate that pesky whitespace:

if (!comment.trim() && comment.length > 100)

(as a side note, none of the above requires jQuery, it's all JavaScript)

edited Apr 3, 2014 at 21:57

answered Apr 3, 2014 at 21:52

SomeKittens

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8 Comments

T.J. Crowder Over a year ago

Why doesn't it work if the OP leaves the field blank, though? "The problem is that if I leave the textarea blank or enter over 100 characters..."

Ori Refael Over a year ago

i related to this in my answer, not handling Trim condition

Ori Refael Over a year ago

!comment just handles case of undefined or null (null in some cases)

SomeKittens Over a year ago

@OriRefael it also handles cases of empty strings, as I've explained.

T.J. Crowder Over a year ago

@SomeKittensUx2666: String#trim is still missing for browsers in significant use in the wild.

|

T.J. Crowder · Accepted Answer · 2014-04-03 22:16:22Z

2

You have two symptoms:

Leaving the field blank doesn't trigger the condition, and
Entering more than 100 characters doesn't trigger the condition.

The others have pointed out why #2 doesn't happen: You're doing comment > 100 where you need comment.length > 100.

The first is most likely because the field isn't completely blank, but rather has some whitespace in it. We can remove that whitespace with jQuery's $.trim (which works cross-browser, whereas .trim on strings doesn't work in IE8). So:

var comment = $.trim($("#comments").val()); // trim removes leading and trailing whitespace
if ((!comment) || (comment.length > 100)) { // Include .length

That's assuming you don't want to count leading and trailing whitespace.

edited Apr 3, 2014 at 22:16

answered Apr 3, 2014 at 21:58

T.J. Crowder

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Comments

Shomz · Accepted Answer · 2014-04-03 21:51:51Z

-1

if ( comment == '' || comment.length > 100 ) {

answered Apr 3, 2014 at 21:51

Shomz

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10 Comments

Scott Over a year ago

But... it works. OP didn't use the .length property to check the length of the comment. (user I am replying to deleted their post)

Shomz Over a year ago

@user2864740 So for you, comment > 100 and comment.length > 100 are the same? Wow...

user2864740 Over a year ago

@Shomz Ahh, yes. Missed that bit in the other change. Just rationally explain/expand the answer.

T.J. Crowder Over a year ago

@Shomz: This is why it's important not just to dump updated code, but to say what you changed, and why. Also: The OP said it didn't work when they left the field blank; this doesn't address that at all.

Shomz Over a year ago

@T.J.Crowder I know and I agree, but this was so straightforward I really thought no explanation was needed. And it does address the empty field.

|

Ori Refael · Accepted Answer · 2014-04-03 21:56:55Z

-2

one reason that everyone here are making a mistake, if i provide an empty string which contains 100 empty spaces they return true.

the current and right way to check for empty string is

if (!comment && comment.trim().length > 100)

trim actually mean that empty spaces from the begining and end of the string are deleted.

answered Apr 3, 2014 at 21:56

Ori Refael

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3 Comments

T.J. Crowder Over a year ago

String#trim is still missing on browsers in significant use in the wild.

Ori Refael Over a year ago

Disagree, works on Opera, I.E, Firefox, Chrome and Avant, also on mobile browsers.

T.J. Crowder Over a year ago

@ Ori: sigh IE8 is still in significant use in the wild (depending who you ask, between 6.2% and 21.4% here in April 2014). And it doesn't have String#trim.

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