如何自动递增，如果我在 text1 上键入 2015，text2 应该显示 2016。

Question

我想要这个，如果我在 text1 上输入 2015，text2 应该显示 2016

Answer 1

function onkey() {

 var year1 = document.getElementById("year1");

 var s = year1.value;

 var year2 = document.getElementById("year2");

 year2.value = +s + 1;

}

Answer 2

也许你只想这样做：

let doc, html, bod, I; // for use on other loads

addEventListener('load', ()=>{

doc = document; html = doc.documentElement; bod = doc.body; I = id=>doc.getElementById(id);

const year1 = I('year1'), year2 = I('year2');

year1.oninput = function(){

  let v = this.value;

  if(v.match(/^[0-9]+$/)){

    year2.value = +v+1;

  }

  else if(v === ''){

    year2.value = '';

  }

}

}); // end load

<input id='year1' type='number' value='' />

<input id='year2' type='number' value='' />