_ExpandingTextAreaMixin.js

define([
	"dojo/_base/declare", // declare
	"dojo/dom-construct", // domConstruct.create
	"dojo/has",
	"dojo/_base/lang", // lang.hitch
	"dojo/on",
	"dojo/_base/window", // win.body
	"../Viewport"
], function(declare, domConstruct, has, lang, on, win, Viewport){

	// module:
	//		dijit/form/_ExpandingTextAreaMixin

	// feature detection, true for mozilla and webkit
	has.add("textarea-needs-help-shrinking", function(){
		var body = win.body(),	// note: if multiple documents exist, doesn't matter which one we use
			te = domConstruct.create('textarea', {
			rows:"5",
			cols:"20",
			value: ' ',
			style: {zoom:1, fontSize:"12px", height:"96px", overflow:'hidden', visibility:'hidden', position:'absolute', border:"5px solid white", margin:"0", padding:"0", boxSizing: 'border-box', MsBoxSizing: 'border-box', WebkitBoxSizing: 'border-box', MozBoxSizing: 'border-box' }
		}, body, "last");
		var needsHelpShrinking = te.scrollHeight >= te.clientHeight;
		body.removeChild(te);
		return needsHelpShrinking;
	});

	return declare("dijit.form._ExpandingTextAreaMixin", null, {
		// summary:
		//		Mixin for textarea widgets to add auto-expanding capability

		_setValueAttr: function(){
			this.inherited(arguments);
			this.resize();
		},

		postCreate: function(){
			this.inherited(arguments);
			var textarea = this.textbox;
			textarea.style.overflowY = "hidden";
			this.own(on(textarea, "focus, resize", lang.hitch(this, "_resizeLater")));
		},

		startup: function(){ 
			this.inherited(arguments);
			this.own(Viewport.on("resize", lang.hitch(this, "_resizeLater")));
			this._resizeLater();
		},

		_onInput: function(e){
			this.inherited(arguments);
			this.resize();
		},

		_estimateHeight: function(){
			// summary:
			//		Approximate the height when the textarea is invisible with the number of lines in the text.
			//		Fails when someone calls setValue with a long wrapping line, but the layout fixes itself when the user clicks inside so . . .
			//		In IE, the resize event is supposed to fire when the textarea becomes visible again and that will correct the size automatically.
			//
			var textarea = this.textbox;
			// #rows = #newlines+1
			textarea.rows = (textarea.value.match(/\n/g) || []).length + 1;
		},

		_resizeLater: function(){
			this.defer("resize");
		},

		resize: function(){
			// summary:
			//		Resizes the textarea vertically (should be called after a style/value change)

			var textarea = this.textbox;

			function textareaScrollHeight(){
				var empty = false;
				if(textarea.value === ''){
					textarea.value = ' ';
					empty = true;
				}
				var sh = textarea.scrollHeight;
				if(empty){ textarea.value = ''; }
				return sh;
			}

			if(textarea.style.overflowY == "hidden"){ textarea.scrollTop = 0; }
			if(this.busyResizing){ return; }
			this.busyResizing = true;
			if(textareaScrollHeight() || textarea.offsetHeight){
				var newH = textareaScrollHeight() + Math.max(textarea.offsetHeight - textarea.clientHeight, 0);
				var newHpx = newH + "px";
				if(newHpx != textarea.style.height){
					textarea.style.height = newHpx;
					textarea.rows = 1; // rows can act like a minHeight if not cleared
				}
				if(has("textarea-needs-help-shrinking")){
					var	origScrollHeight = textareaScrollHeight(),
						newScrollHeight = origScrollHeight,
						origMinHeight = textarea.style.minHeight,
						decrement = 4, // not too fast, not too slow
						thisScrollHeight,
						origScrollTop = textarea.scrollTop;
					textarea.style.minHeight = newHpx; // maintain current height
					textarea.style.height = "auto"; // allow scrollHeight to change
					while(newH > 0){
						textarea.style.minHeight = Math.max(newH - decrement, 4) + "px";
						thisScrollHeight = textareaScrollHeight();
						var change = newScrollHeight - thisScrollHeight;
						newH -= change;
						if(change < decrement){
							break; // scrollHeight didn't shrink
						}
						newScrollHeight = thisScrollHeight;
						decrement <<= 1;
					}
					textarea.style.height = newH + "px";
					textarea.style.minHeight = origMinHeight;
					textarea.scrollTop = origScrollTop;
				}
				textarea.style.overflowY = textareaScrollHeight() > textarea.clientHeight ? "auto" : "hidden";
				if(textarea.style.overflowY == "hidden"){ textarea.scrollTop = 0; }
			}else{
				// hidden content of unknown size
				this._estimateHeight();
			}
			this.busyResizing = false;
		}
	});
});