javascript total sum of array values

Question

Trying to create form to add up values from units array. Can't get function Calc_totals to work.

<script language="JavaScript" type="text/javascript">
function Calc(form) {

    var drink = new Array()
    drink [0] = form.drink0.value;
    drink [1] = form.drink1.value;
    drink [2] = form.drink2.value;

    var units = new Array()
    units [0] = 25;
    units [1] = 50;
    units [2] = 75;

    var number_units = new Array()
    form.units0.value = form.drink0.value * units[0];
    form.units1.value = form.drink1.value * units[1];
    form.units2.value = form.drink2.value * units[2]; 
    } 

function Calc_totals() {
    var answerValue = 0; 
    for(i=0; i < units.length; i++) 
    { 
    answerValue += Number(units[i]);
    } 
    form.total_units.value = answerValue;
}
</script>

I want the function Calc_totals to the total of units and output to form.total_units.value.

HTML:

<form name="calc_form" id="form" method="post">
   <table width="370" border="0" bgcolor="#EAEAEA">
<tr>
<th width="141"><h2>Drink Type</h2></th><th width="55"><h2>Number drank</h2></th>
<th width="84"><h2>Units</h2></th>
<th width="84"><h2>Calories</h2></th>
</tr>
   <tr class="table-text">
     <td class="right"><p class="table-text">Cider (4.5%)</p>
       <p class="table-text">1 x 568ml pint</p>
       <p class="table-text">e.g. Magners, Strongbow</p></td>
    <td width="55" valign="top">
      <p class="table-text">
     <input name="drink0" type="text" id="drink0" size="3" maxlength="2" onchange="Calc(form);" />
      </p></td>
    <td width="84" valign="top"><p class="table-text">
      <input name="units0" type="text" id="units0" size="4" maxlength="3" />
    </p></td>
    <td width="84" valign="top"><p class="table-text">
      <input name="calories0" type="text" id="calories0" size="4" maxlength="3" />
    </p></td>
    </tr>
<tr>
    <td class="right"><p class="table-text">Cider (7.5%)</p>
      <p class="table-text">1 x 500ml can</p></td>
    <td width="55" valign="top" class="table-text"><p class="table-text">
      <input name="drink1" type="text" id="drink1" size="3" maxlength="2" onchange="Calc(form);" />
    </p></td>
    <td width="84" valign="top"><p class="table-text">
      <input name="units1" type="text" id="units1" size="4" maxlength="3" />
      </span></p></td>
    <td width="84" valign="top"><p class="table-text">
      <input name="calories1" type="text" id="calories1" size="4" maxlength="3" />
      </span></p></td>
    </tr>
<tr>
    <td class="right"><p class="table-text">Beer (5%)</p>
      <p class="table-text">1 x 330ml bottle </p>
      <p class="table-text">e.g. Grolsch, Budweiser</p></td>
    <td width="55" valign="top" class="table-text"><p class="table-text">
      <input name="drink2" type="text" id="drink2" size="3" maxlength="2" onchange="Calc(form);" />
    </p></td>
    <td width="84" valign="top"><p class="table-text">
      <input name="units2" type="text" id="units2" size="4" maxlength="3" />
    </p></td>
    <td width="84" valign="top"><p class="table-text">
      <input name="calories2" type="text" id="calories2" size="4" maxlength="3" />
    </p></td>
    </tr>

<tr>
  <td><p class="table-text">&nbsp;</p></td>
  <td width="55" valign="top"><p class="table-text"></p></td>
  <td width="84" valign="top">&nbsp;</td>
  <td width="84" valign="top"><p class="table-text"></p></td>
</tr>

<tr>
  <td><p class="table-text"><strong>Totals per week= </strong></p></td>
  <td width="55" valign="top"><p class="table-text">&nbsp;</p></td>
  <td width="84" valign="top"><p class="table-text">
    <input name="total_units" type="text" id="total_units" size="4" maxlength="3" /> 
    units  </p></td>
  <td width="84" valign="top"><p class="table-text">
    <input name="total_calories" type="text" id="total" size="4" maxlength="3" />
  kcals</p></td>
</tr> 

<tr>  
<td colspan="2"><INPUT name="reset" value="Reset" TYPE="reset"> </td>
<td colspan="3"><input name="Calculate Total" type="button" id="Calculate Total" value="Calculate Total" onclick="Calc_totals();" /></td>
</tr>
</table>
</form>

I want the total of units. Thanks for any help.

Solution

The problem with this code is that units is not visible inside Calc_totals. You have a few options:

• make it global (bad option)
• pass it as an argument

Alternatively, you can calculate the sum using reduce (ECMAScript 5 feature - doesn't work in older browsers)

var sum = units.reduce(function(a, b) { return a + b });

And ES6 version

var sum = units.reduce((a, b) => a + b);

Comments

[Lukasz Madon]

@jmill23 the easy way to fix it is to move unit outside the function var units = [];

[jmill23]

There will be too many variables in units array to use this function. Tried the loop but not working.

[jmill23]

how to I call it from above function and pass it through a loop. Problem seems to be that Calc_totals is not getting values from units?

[Vishy]

I said define it outside Calc() "Not In Calc()" and make it global. Delete the units definition inside Calc(). Calc_totals is unable to see that array because it is Local to Calc().

[jmill23]

Error seems to be with the for loop. var answerValue = 0; for(i=0; i < units.length; i++) { answerValue += Number(units[i].value); } form.total_units.value = answerValue; If I remove the for loop: var answerValue = 0; form.total_units.value = answerValue; I get a vlaue of 0. So it's not getting values from units[i]?

[Vishy]

Yes it is not getting value units. As I told you earlier define units array as a global variable instead of local variable.

[jmill23]

Ok, I understand what you mean now, but I don't know how to do that. Can you give example code please? Thanks.

[jmill23]

Thanks @Vishwanath. I've amended function Calc. Problem is I want this to run indpependantly of Calc_totals using onChange the unit values are calculated. Then onSubmit, I want the total sum of units to appear as a value in field form.total_units.

[jmill23]

Ok, i have got the loop working, but it's taking the values from the array, I want the values from the form units0.value, units1.value etc...