学步园

//以下是获取textarea中光标的位置
	var start=0;
	var end=0;
	function savePos(textBox) {
		//如果是Firefox(1.5)的话，方法很简单
		if (typeof (textBox.selectionStart) == "number") {
			start = textBox.selectionStart;
			end = textBox.selectionEnd;
		}
		//下面是IE(6.0)的方法，麻烦得很，还要计算上'\n'
		else if (document.selection) {
			var range = document.selection.createRange();
			if (range.parentElement().id == textBox.id) {
				// create a selection of the whole textarea
				var range_all = document.body.createTextRange();
				range_all.moveToElementText(textBox);
				//两个range，一个是已经选择的text(range)，一个是整个textarea(range_all)
				//range_all.compareEndPoints()比较两个端点，如果range_all比range更往左(further to the left)，则                //返回小于0的值，则range_all往右移一点，直到两个range的start相同。
				// calculate selection start point by moving beginning of range_all to beginning of range
				for (start = 0; range_all.compareEndPoints("StartToStart",
						range) < 0; start++)
					range_all.moveStart('character', 1);
				// get number of line breaks from textarea start to selection start and add them to start
				// 计算一下\n
				for ( var i = 0; i <= start; i++) {
					if (textBox.value.charAt(i) == '\n')
						start++;
				}
				// create a selection of the whole textarea
				var range_all = document.body.createTextRange();
				range_all.moveToElementText(textBox);
				// calculate selection end point by moving beginning of range_all to end of range
				for (end = 0; range_all.compareEndPoints('StartToEnd', range) < 0; end++)
					range_all.moveStart('character', 1);
				// get number of line breaks from textarea start to selection end and add them to end
				for ( var i = 0; i <= end; i++) {
					if (textBox.value.charAt(i) == '\n')
						end++;
				}
			}
		}
	}