javascript - 在 javascript 中添加输入时未定义的输出

Question

尝试制作 BMR 计算器作为家庭作业。我想我已经弄清楚了大部分内容，但我的输出字段中的输出为“未定义”。这是代码:

<input class="boks" placeholder="vekt i kg" id="vekt" type="text">

<input class="boks" placeholder="høyde i cm" id="hoyde" type="text">

<input class="boks" placeholder="alder" id="alder" type="text">

<button id="beregn" onclick="utregning()">Regn ut din BMR</button>

<input class="boks" placeholder="Din BMR" id="output" type="text" 
readonly="true">

js:

var konstant = 66.5;

var vekt = parseInt(document.getElementById("vekt").value);

var vektutr = vekt*13.75;

var hoyde = parseInt(document.getElementById("hoyde").value);

var hoydeutr = hoyde*5.003;

var alder = parseInt(document.getElementById("alder").value);

var alderutr = alder*6.755;

var sum = +konstant + +vektutr + +hoydeutr - +alderutr;

function utregning() {

document.getElementById("output").value = sum;

}

Answer 1

您需要从函数内部的输入中获取所有值，因为函数外部的代码将在调用utregning之前执行，此时输入字段的值为空

var konstant = 66.5;



function utregning() {
  var vekt = parseInt(document.getElementById("vekt").value);

  var vektutr = vekt * 13.75;

  var hoyde = parseInt(document.getElementById("hoyde").value);

  var hoydeutr = hoyde * 5.003;

  var alder = parseInt(document.getElementById("alder").value);

  var alderutr = alder * 6.755;

  var sum = +konstant + +vektutr + +hoydeutr - +alderutr;

  document.getElementById("output").value = sum;

}

<input class="boks" placeholder="vekt i kg" id="vekt" type="text">

<input class="boks" placeholder="høyde i cm" id="hoyde" type="text">

<input class="boks" placeholder="alder" id="alder" type="text">

<button id="beregn" onclick="utregning()">Regn ut din BMR</button>

<input class="boks" placeholder="Din BMR" id="output" type="text" readonly="true"> js: