css/css-values/calc-unit-analysis.html

<!DOCTYPE HTML>
<html>
<head>
  <title>CSS Variables Allowed Syntax</title>
  <link rel="author" title="L. David Baron" href="https://dbaron.org/">
  <link rel="author" title="Mozilla Corporation" href="http://mozilla.com/" />
  <link rel="help" href="http://www.w3.org/TR/css3-values/#lengths" />
  <link rel="help" href="http://www.w3.org/TR/css3-values/#calc-type-checking" />
  <script src="/resources/testharness.js"></script>
  <script src="/resources/testharnessreport.js"></script>
<style id="style"></style>
</head>
<body>
<div id=log></div>
<div id="test"></div>
<script>

function run() {
  var test_elt = document.getElementById("test");
  var test_cs = window.getComputedStyle(test_elt, "");

  function description_to_name(description) {
    return description.replace(/\W+/g, "_").replace(/^_/, "").replace(/_$/, "");
  }

  function assert_invalid_value(property, value, description) {
    test(function() {
           test_elt.style.setProperty(property, "inherit");
           test_elt.style.setProperty(property, value);
           assert_equals(test_elt.style.getPropertyValue(property),
                         "inherit");
           test_elt.style.setProperty(property, value);
           test_elt.style.removeProperty(property);
         },
         description_to_name(description));
  }

  function assert_valid_value(property, value, computes_to, description) {
    test(function() {
           test_elt.style.setProperty(property, "inherit");
           test_elt.style.setProperty(property, value);
           assert_not_equals(test_elt.style.getPropertyValue(property),
                             "inherit");
           assert_equals(test_cs.getPropertyValue(property),
                         computes_to);
           test_elt.style.removeProperty(property);
         },
         description_to_name(description));
  }

  assert_invalid_value("margin-left", "calc(0)", // invalid calc expression
                       "unitless zero in calc() is a numeric type, not length");
  assert_valid_value("margin-left", "calc(0px)", "0px",
                     "0px in calc()");
  assert_invalid_value("margin-left", "calc(1px + 2)", // invalid calc expression
                       "addition of length and number");
  assert_invalid_value("margin-left", "calc(2 + 1px)", // invalid calc expression
                       "addition of number and length");
  assert_invalid_value("margin-left", "calc(1px - 2)", // invalid calc expression
                       "subtraction of length and number");
  assert_invalid_value("margin-left", "calc(2 - 1px)", // invalid calc expression
                       "subtraction of number and length");
  assert_valid_value("margin-left", "calc(2px * 2)", "4px",
                     "multiplication of length and number");
  assert_valid_value("margin-left", "calc(2 * 2px)", "4px",
                     "multiplication of number and length");
  assert_invalid_value("margin-left", "calc(2px * 1px)", // invalid calc expression
                       "multiplication of length and length");
  assert_invalid_value("margin-left", "calc(20 / 0.75rem)", // invalid calc expression
                       "division by non-number");
}

run();

</script>
</body>
</html>