javascript - 如何将文本区域的最后三行添加到三个不同的变量？

Question

我有一个带有 textarea 标签的 html 文件，我将在其中复制和粘贴一些多行文本，我想使用 javascript 在三个不同的变量中分别获取最后三行。textarea 被分配了一个 id="txt"。点击的函数被分配给 html 文件中的按钮。

function clicked(){
var txt = document.getElementById("txt");
var original = txt.value; //original text transfered to original variable

var lastline =  //add last line in this variable

var secondlast = //add second last line in this variable

var thirdlast = //add third last line in this variable

var modified = //add text without these three lines in this variable


console.log(lastline); //how are you
console.log(secondlast); //now is the time
console.log(thirdlast); //helloo  there
console.log(modified); //school data is the important
//checking home
//not there
}

textarea中输入的文字:

school data is the important
checking home
not there
helloo  there
now is the time
how are you

输出:

how are you

now is the time

helloo  there

school data is the important
checking home
not there

Answer 1

简单的功能:

function letsgo() {
  var area= document.getElementById("mytext"),
  //get all the lines in the textarea, seperated by \n or \r\n
      lines = area.value.match(/[^\r\n]+/g),
  //get bottom 3 lines, reverse them
      bottom3 = lines.slice(-3).reverse();

  var lastline=bottom3[0];
  var secondlast=bottom3[1];
  var thirdlast=bottom3[2];

  //get all text except bottom 3 lines, joining them together with linefeed again
  var rest = lines.slice(0, -3).join("\n");

  //glue bottom3 and rest together
  var result=bottom3.join("\n")+"\n"+rest;

  //put in the textarea again
  area.value=result;
}