我试图建立一个网站，javascript 数学不起作用

Question

I'm trying to use codepen.io to make a website to sell things (not really "sell" things), but for some reason the calculations with the javascript won't work, I'm trying to make it calculate the total and display it in a text-field. Here is the javascript.

function doFunction(){

   var shirtNo, bearNo, pillowNo, totalNo; 
   var shirtNo =  document.getElementById("panda_shirt").value;
   bearNo = document.getElementById("panda_toy").value;
   pillowNo =    document.getElementById("panda_pillow").value;
   var totalQty = panda_shirt + panda_toy + panda_pillow ,
     estimateTotal;
   estimateTotal = ($14 * panda_shirt) + ($12 * panda_toy) + ($10 * 
   panda_pillow);
  
   document.getElementById('estimateTotal').value = Estimate Total;
}

Answer 1

You had some syntax errors. Try the code below. This will give you the total price, then you can use it however you'd like.

  function doFunction(){ 
     var shirtNo =  document.getElementById("panda_shirt").value;
     var bearNo = document.getElementById("panda_toy").value;
     var pillowNo = document.getElementById("panda_pillow").value;
     var estimateTotal = (14 * Number(shirtNo)) + (12 * Number(bearNo)) + (10 * Number(pillowNo));

Answer 2

'$14' is not a number.

computers are perfect at math. that's their primary function. so if the math is wrong, it's your code, not the computer or the language.

also you have not defined panda_shirt or your other variables, so it appears you are attempting to do math with undefined objects.

try adding console.log() statements to your code so you can see what variable values you are dealing with.

Answer 3

Javascript is a dynamically typed language. The type of a variable is defined by the value it contains.

So, In your code, the variables shirtNo , bearNo , pillowNo most probably contain string values - because they seems to be read from HTML text elements.

In order to perform mathematical operations, the variables must contain number values. You can convert a string value to a number by using the Number function.

Number(shirtNo)

Also, $14 will not give it a Dollar value. A number is just a number in Javascript. The currency is only an interpretation.

So, you can rewrite your code like this:

 function doFunction(){

   var shirtNo, bearNo, c; 

   shirtNo =  document.getElementById("panda_shirt").value;
   bearNo = document.getElementById("panda_toy").value;
   pillowNo = document.getElementById("panda_pillow").value;


   estimateTotal = (14 * Number(shirtNo)) + (12 * Number(bearNo)) + (10 * Number(pillowNo));
  
   document.getElementById('estimateTotal').value = estimateTotal;
 }

However, it may not be that the user has entered a numerical value in the inputs. In that case the function isNaN() can tell you if any value is Not A Number.

Answer 4

You need to convert the value of bearNo to an int or float number. Otherwise, it will be count as a string. And $14 doesn't work like this. You can't use a $ sign when multiplying with numbers.