如何用纯javascript检测textarea大小的变化？

Question

我想在textarea的大小发生变化时发出通知，当时发生了什么事，我该如何检测呢？

Answer 1

Here is a small example using pure (without jQuery etc. dependencies) Javascript.

It's using mouseup and keyup handlers and an optional intervall to detect changes.

var detectResize = (function() {

  function detectResize(id, intervall, callback) {
    this.id = id;
    this.el = document.getElementById(this.id);
    this.callback = callback || function(){};

    if (this.el) {
      var self = this;
      this.width = this.el.clientWidth;
      this.height = this.el.clientHeight;

      this.el.addEventListener('mouseup', function() {
        self.detectResize();
      });

      this.el.addEventListener('keyup', function() {
        self.detectResize();
      });

      if(intervall) setInterval(function() {
          self.detectResize();
      }, intervall);

    }
    return null;
  }

  detectResize.prototype.detectResize = function() {
      if (this.width != this.el.clientWidth || this.height != this.el.clientHeight) {
        this.callback(this);
        this.width = this.el.clientWidth;
        this.height = this.el.clientHeight;
      }
  };

  return detectResize;

})();

Usage: new detectResize(element-id, intervall in ms or 0, callback function)

Example:

<textarea id="mytextarea"></textarea>
<script type="text/javascript">
var mytextarea = new detectResize('mytextarea', 500, function() {
  alert('changed');
});
</script>

See it in action on jsfiddle.net/pyaNS .

Answer 2

You can use library agnostic JavaScript (assuming you're not using jQuery or are using another library) by doing:

<textarea id="t"></textarea>
<script>
    var t = document.getElementById('t'),
        tHeight = t.clientHeight,
        tWidth = t.clientWidth;

    console.log(t);

    t.onmouseup = function (e) {
        if (tHeight !== t.clientHeight || tWidth !== t.clientWidth ) { 
            console.log('size change');
            tHeight = t.clientHeight;
            tWidth = t.clientWidth;
        }
    };
</script>

I've included a console log of the element so you can see which events you can tap into in your inspector.

Answer 3

You can intercept the mouse events of the user, when he tries to change the size of the textarea.

1: Element .addEventListener("mousedown", event => {}) : Start interception.

2: window .addEventListener("mousemove", event => {}) : Here a comparison between the previous and the current size of each move event take place.

3. window .addEventListener("mouseup", event => {}) : Stop interception.

demo: https://codepen.io/martinwantke/pen/QaJqgq

Answer 4

Try this Demo.

http://jsfiddle.net/vol7ron/Z7HDn/

jQuery(document).ready(function(){
   var $textareas = jQuery('textarea');

   // set init (default) state   
   $textareas.data('x', $textareas.outerWidth());
   $textareas.data('y', $textareas.outerHeight()); 

   $textareas.mouseup(function(){

      var $this = jQuery(this);

      if (  $this.outerWidth()  != $this.data('x') 
         || $this.outerHeight() != $this.data('y') )
      {
          alert( $this.outerWidth()  + ' - ' + $this.data('x') + '\n' 
               + $this.outerHeight() + ' - ' + $this.data('y')
               );
      }

      // set new height/width
      $this.data('x', $this.outerWidth());
      $this.data('y', $this.outerHeight()); 
   });

});

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Cannot make it in pure javascript we must use jQuery