在按键上从文本区域获取最后一行 [英] Get last line from a textarea on keypress

问题描述

我有一个textarea字段，每次按键时，我想将textarea中的最后一行推到一个数组中.

I have a textarea field and on every keypress, I would like to push the last line in the textarea to an array.

当前，我在每次按键时都构造一个数组，以获取文本区域的最后一行.有没有一种方法可以对此进行优化?意思是，无需构造数组即可获得文本区域的最后一行.

Currently, I am constructing the array on every keypress to get the last line in the textarea. Is there a way to optimize this? Meaning, get last line in the textarea without having to construct an array.

jQuery('#mytextarea').keypress(function() {
    lines = jQuery('#mytextarea').text().split("\n");
    lastLine = lines[lines.length - 1];

});

if(.. some condition ..) {
myArray.push(lastLine);

推荐答案

实际上，有一种方法可以对此进行优化.优化主要是内存使用-实际CPU使用也得到了改善.

Indeed, there is a way to optimize this. The optimization is mostly memory usage - the actual CPU usage is also improved.

优化版本依赖于lastIndexOf().如下:

The optimized version relies on lastIndexOf(). It is as follows:

jQuery("#mytextarea").keypress(function() {
     var content = this.value;
     var lastLine = content.substr(content.lastIndexOf("\n")+1);
});

您会注意到一些微观优化:

You will notice a couple of micro-optimizations:

• this已经是DOM元素.重新调用jQuery只是为了获取文本内容没有什么意义.在处理器上节省一点时间
• 使用lastIndexOf可使我在最后一个\n
之后得到任何东西

• this already is the DOM element. There is little point in re-invoking jQuery just to get the text content. Saves a bit on processor
• using lastIndexOf allows me to get anything after the last \n

Dogbert 为lastIndexOf提供了基准: 查看全文