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我一直在尝试使用Javascript和HTML编写一个简单的计算器。我对Javascript知之甚少，之后跟随一些教程来构建以下代码。我打算制作的计算器有两个字段（电池电流和负载电流）。我需要用电池电流除以负载电流乘以电流单位，当我点击计算或更改值时应显示结果值。

var current_unit = new Array();
current_unit["mA"] = 1000;
current_unit["A"] = 1;

function getbattunit() {
    var currentunit1 = 0;
    var theForm1 = document.forms[batterycalculator];
    var unit1 = theform.elements["currunit"];
    var Amps1 = current_unit[unit.value];
    return Amps1;
}

function getloadunit() {
    var currentunit2 = 0;
    var theForm2 = document.forms[batterycalculator];
    var unit2 = theform.elements["loadunit"];
    var Amps2 = current_unit[unit.value];
    return Amps2;

}

function runtime() {
    var currentunit = 0;
    var theForm = document.forms[batterycalculator];
    var temp = theform.elements["loadcurr"];
    var temp1 = the form.elemets["battcurr"];
    var time = (getbattunit() * battcurr) / (getloadunit() * loadcurr); 
     document.getElementById('timeresult').innerHTML =
        "Load can be powered for" + time;

    }

<form action="" id="batterycalculator" onsubmit="return false">
        <div>
            <div class="cont_order">
               <fieldset>
                <legend>Battery life calculator</legend>
                 <label for='loadcurr'>Load current</label>
                <input type="number" id="loadcurr" name='loadcurr' />
                 <select id="currunit" name='currunit' onchange="runtime()">
                <option value="A">A</option>
                <option value="mA">mA</option>
               </select>
                 <br/>
                <br/>
                 <label for='battcurr'>Battery maximum capacity</label>
                <input type="number" id="battcurr" name='battcurr' />
                <select id="loadunit" name='loadunit' onchange="runtime()">
                <option value="A">A</option>
                <option value="mA">mA</option>
               </select>
                 <br/>
                 <br/>
                 <div id="timeresult"> </div>                 
                 </br>
                 <button value='Submit' onclick="runtime()" />Calculate</button>
                 <br/>
                </fieldset>
          </div>
        </div>  
       </form>

Javascript计算器执行除法