Getting a error when click save and I am unable to create new number

Question

When I click on save on my bootstrap modal button it tries to find next available number.

How ever if returns null throws error.

TypeError: matches is null

Question When click on save in bootstrap modal if no numbers found in textarea then will create a number. Currently if no findAvailableNumber function returns null unable to create a number

Codepen Example

$('#myLink').on('shown.bs.modal', function() {
    var text = getSelectedText();
    $('#title').val(text.trim());
    $('#url').val('http://');
});    

function getSelectedText() {
    var textarea = document.getElementById("message");
    var len = textarea.value.length;
    var start = textarea.selectionStart;
    var end = textarea.selectionEnd;
    var sel = textarea.value.substring(start, end);
    return sel;
}

function findAvailableNumber(textarea){
      //Find lines with links
    var matches = textarea.value.match(/(^|\n)\s*\[\d+\]:/g);

    //Find corresponding numbers
    var usedNumbers = matches.map(function(match){
        return parseInt(match.match(/\d+/)[0]); }
    );

    //Find first unused number
    var number = 1;

    while(true){
        if(usedNumbers.indexOf(number) === -1){
            //Found unused number
            return number;
        }

        number++;
    }

    return number;
}

$('#save-link').on('click', function(e) {
    var textarea = document.getElementById("message");
    var len = textarea.value.length;
    var start = textarea.selectionStart;
    var end = textarea.selectionEnd;
    var sel = textarea.value.substring(start, end);

    var counter = findAvailableNumber(textarea);

    var replace = '[' + $('input#title').val() + ']' + '[' + counter + ']';

    var id = '\n   [' + counter + ']: ' + $('input#url').val();

    if ($('#title').val().length > 0) {
        textarea.value = textarea.value.substring(0,start) + replace +
        textarea.value.substring(end,len) + id;
    } else {

        return false;
    }
});

How links look in textarea when created.

[exmple-1][1] and [example-2][2]

[1]: http://www.example.com
[2]: http://www.example.com

Answer 1

You need to check to see if the <textarea> actually has a value within findAvailableNumber() . If not, return 1 to kick it off.

function findAvailableNumber(textarea){
    var number = 1;
    if(textarea.value){

      //Find lines with links
      var matches = textarea.value.match(/(^|\n)\s*\[\d+\]:/g);

      //Find corresponding numbers
      var usedNumbers = matches.map(function(match){
          return parseInt(match.match(/\d+/)[0]); }
      );

      //Find first unused number
      var number = 1;

      while(true){
          if(usedNumbers.indexOf(number) === -1){
              //Found unused number
              return number;
          }

          number++;
      }
    }

    return number;
}

Here's an updated pen.