How can I replicate a set of characters every time they are typed using JavaScript?

Question

I currently have a form and what I would like is that every time a "Tag" is mentioned, denoted by being surrounded by double square brackets (i.e [[Tag]]), the same tag is repeated once.

This would mean that when I type [[Tag]], I would immediately see [[Tag]][[Tag]]. This idea is that someone would then be able to type text in between the two tags.

I have the following JavaScript:

function newNote() {
    const note_button = document.getElementById("new_note_button")
    const note = document.getElementById("new_note_form_container");
    if (note.style.display === "none") {
      note.style.display = "block";
      note_button.innerHTML = "Only show notes"
    } else {
      note.style.display = "none";
      note_button.innerHTML = "Create a new note"
    }
  }

  document.addEventListener('DOMContentLoaded', function(){
    let input_note = document.getElementById('note_text');
    input_note.addEventListener('input', upThing)
})

function upThing(ev) {

    let note_form = ev.target.value;
    let regex = /(?=$$\[).*?(?<=$$\])/g;
    let first_position = 0;
    let result = note_form.substring(first_position);
    
    let open_bracket = result.indexOf("[[") + 2;
    let close_bracket = result.indexOf("]]");
    if (close_bracket > open_bracket) {
        let tag = result.substring(open_bracket, close_bracket);
        console.log(tag)
        ev.target.value = ev.target.value + "[[" + tag + "]]";
    }

}

This JavaScript does produce the desired [[Tag]] to [[Tag]][[Tag]]. However, every time I continue to type another [[Tag]] appears. So this does not serve the purpose.

I need it so that I can repeat this process for [[Tag 2]], [[Tag 3]] etc.

It would be helpful to understand how to move the tags to bold when enclosed by [[ ]]

user_3807365 · Answer

This will work when the ]] is at the end of string. This can be extended to any position though.

Update: should work even if on middle of text.

document.querySelector('.btex').addEventListener('keyup', function(ev) {
  if (ev.key == ']') {
    var val = this.value;
    var start = this.selectionStart;

    if (start > 1 && val.substring(start - 2, start) == "]]") {
      var pos = val.lastIndexOf("[[", start);
      var word = val.substring(pos, pos + start);

      if (start > pos) {
        var end = this.selectionEnd;
        this.value = val.substring(0, start) + word + val.substring(end);
        this.selectionStart = this.selectionEnd = start;
        return false;
      }
    }
  }
});

How can I replicate a set of characters every time they are typed using JavaScript?

1 Answers