Question

How can I prevent the user from inserting more than one line break in a row into a text field?
I prefer a solution using jQuery.

UPDATE 1:

I have inserted anadeo’s code into my code which looks like the following. Unfortunately it doesn’t work – it still allows more than one line break in a row in the textarea #posttext. Anyone know how to fix this? Thanks 🙂

//Post something
$('#postDiv').on('keydown', '#posttext', function(e) {
if (e.which==13 && !e.shiftKey && $('#posttext').val()!=' Post something...') {

    var last = false;

    var code = (e.keyCode ? e.keyCode : e.which);
    if(code == 13) {
        if (last) { e.preventDefault(); }
        last=true;
    }else{
        last=false;
    }

    //If not currently loading and enough text typed in, submit
    if($('#imageFeedback').html()!=' | Loading...' && $('#posttext').val().length>15){

        //Say that it is loading
        $('#imageFeedback').css('color','black').css('font-weight','normal').html(' | Loading...');

        //Call function to post
        post($(this));
        return false;
    }
}
});

Answer 1

$(textarea).on('keydown', function(e) {
    var code = (e.keyCode ? e.keyCode : e.which);
    if(code == 13 && this.value.match(/\n/g)) e.preventDefault();
});​

FIDDLE

...more than one line break in a row

Are you thinking of avoiding more than one line break in a row (one after another), like so:

var last = false;

$(textarea).on('keydown', function(e) {
    var code = (e.keyCode ? e.keyCode : e.which);
    if(code == 13) {
        if (last) { e.preventDefault(); }
        last=true;
    }else{
        last=false;
    }
});​

FIDDLE

EDIT:

Firstly, on() is only supported in jQuery 1.7+, so make sure you are using a newer version of the library.

You are also using the delegated version of on(), and that should’nt be a problem, but it assumes that your textarea is inserted into the DOM at a later time, and not present from the start, ie. it’s dynamically inserted with JS etc.

The rest seems ok, but the last variable will have to be placed outside the keydown function to work properly, and the var code should be at the top, doing the check for the enter key only once, as the second check is not really necessary.
The code variable is really optional, as jQuery is supposed to normalize e.which, but doing a check to see if keycode or which is supported seems like a good idea to ensure cross browser compatibility.

The check for the #posttext value will only work once, as soon as a linebreak is entered the value is no longer Post something..., and the “limit linebreaks” function will be enabled?

All in all I think this should work, try it and see ?

var last = false;

$('#postDiv').on('keydown', '#posttext', function(e) {
    var code = (e.keyCode ? e.keyCode : e.which);
    if (code==13 && !e.shiftKey && $('#posttext').val()!=' Post something...') {
        if (last) { e.preventDefault(); }
        last=true;
    }else{
        last=false;
    }
});​

FIDDLE

Also, It would probably be a good idea to use a less common variable name instead of last, something like MyLastTyped, PostTextLast etc. that is less likely to be confused with a function or variable with the name last in some other place or plugin etc.