Pen Settings

HTML

CSS

CSS Base

Vendor Prefixing

Add External Stylesheets/Pens

Any URL's added here will be added as <link>s in order, and before the CSS in the editor. You can use the CSS from another Pen by using it's URL and the proper URL extention.

+ add another resource

JavaScript

Babel includes JSX processing.

Add External Scripts/Pens

Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

+ add another resource

Packages

Add Packages

Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

Behavior

Save Automatically?

If active, Pens will autosave every 30 seconds after being saved once.

Auto-Updating Preview

If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.

Format on Save

If enabled, your code will be formatted when you actively save your Pen. Note: your code becomes un-folded during formatting.

Editor Settings

Code Indentation

Want to change your Syntax Highlighting theme, Fonts and more?

Visit your global Editor Settings.

HTML

              
                <main>

  <h1>Prevent numeric form input invalidity</h1>

  <p>Prevent illegal input while entering numbers into form fields which perform real-time calculations.</p>
  
  <p>Behaviour update for the <a href="https://websemantics.uk/tools/convert-pixel-point-em-rem-percent/" target=_blank title="[new window]">Font-size converter</a> on webSemantics.</p>

  <form class=frm aria-labelledby=frm_ttl>

    <h2 id=frm_ttl class=-visually-hidden>Font-size conversion calculator</h2>

    <div class=frm_fld-root>
        <label class=frm_lbl-root>
          <span class=lbl_txt>Browser default font-size </span>
          <span class=-nowrap>
            <input class=IN-rootFS type=number>
            px
          </span>
        </label>
    </div>

    <div class=frm_fld-convert>

      <label class=frm_lbl>
        <span class=lbl_txt>Convert<span class=-visually-hidden> font-size</span></span>
        <input class=IN-fromFS type=text data-allowNegative>
      </label>

      <fieldset class=frm_set>

        <legend class=-visually-hidden>From:</legend>

        <label class=IN_lbl-radio>
          <span class=lbl_txt>px</span>
          <input class="IN_radio-from" type=radio name=unitFrom id=IN_radio_from-px value=px>
          <span></span>
        </label>

        <label class=IN_lbl-radio>
          <span class=lbl_txt>%</span>
          <input class="IN_radio-from" type=radio name=unitFrom id=IN_radio_from-percent value=percent>
          <span></span>
        </label>

        <label class=IN_lbl-radio>
          <span class=lbl_txt>pt</span>
          <input class="IN_radio-from" type=radio name=unitFrom id=IN_radio_from-pt value=pt>
          <span></span>
        </label>

        <label class=IN_lbl-radio>
          <span class=lbl_txt>rem</span>
          <input class="IN_radio-from" type=radio name=unitFrom id=IN_radio_from-rem value=rem checked>
          <span></span>
        </label>

      </fieldset>

    </div>


    <div class=frm_fld-result>

      <label class=frm_lbl aria-live=polite>
        <span class=lbl_txt>Result</span>
        <input class=IN-toFS type=text readonly>
        <span class="IN_toUnit -visually-hidden">REM</span>
      </label>

      <fieldset class=frm_set>

        <legend class=-visually-hidden>Change result unit to:</legend>

        <label class=IN_lbl-radio>
          <span class=lbl_txt>px</span>
          <input class=IN_radio-to type=radio name=unitTo id=IN_radio_to-px value=px  checked>
          <span></span>
        </label>

        <label class=IN_lbl-radio>
          <span class=lbl_txt>%</span>
          <input class=IN_radio-to type=radio name=unitTo id=IN_radio_to-percent value=percent>
          <span></span>
        </label>

        <label class=IN_lbl-radio>
          <span class=lbl_txt>pt</span>
          <input class=IN_radio-to type=radio name=unitTo id=IN_radio_to-pt value=pt>
          <span></span>
        </label>

        <label class=IN_lbl-radio>
          <span class=lbl_txt>rem</span>
          <input class=IN_radio-to type=radio name=unitTo id=IN_radio_to-rem value=rem>
          <span></span>
        </label>

      </fieldset>

    </div>

    <div style=text-align:right aria-live=polite>
      [<span id=svg_from></span> = <span id=svg_to></span>]
      &mdash; Version 5.0
    </div>
  </form>
  
  <p>Try typing into the <i>Convert</i> field. See how the <i>Result</i> is updated live, as you type, but only while the <i>Convert</i> value is valid. Test starting with a period (.) or lead zero, or a zero after a period.</p>
  
  <p><b>Updated November 2021</b> to replace <code>event.which</code> keyboard detection, and also to allow negative mumbers. Test adding a minus at the front, middle, end, with and without period.</p>
  
  <p>If I've done it correctly, it should be impossible to enter invalid characters, or break the calculation.</p>

</main>

<!-- Footer codepen include -->
[[[https://codepen.io/2kool2/pen/mKeeGM]]]
              
            
!

CSS

              
                /* Generic styling */
*, *::after, *::before {box-sizing: inherit;}
body {
  --color: hsl(269, 19%, 30%);
  --bgColor: hsla(32,100%,85%,.35);
  --linkColor: hsla(214, 71%, 47%, 1);
  --linkColorUnderline: hsla(214, 71%, 47%, .5);
  --linkColorHover: hsla(214, 100%, 35%, 1);
  --linkBgHover: hsla(214, 100%, 85%, 1);
  --linkFocus: hsla(214, 71%, 80%, 0.3);
  --focusOutline: hsla(214, 71%, 85%, 1);

  --textShadow: #fff;
  --boxShadow: hsla(0,0%,0%,.3);
  --bgColorForm: hsla(120,50%,50%,.075);

  font-family: sans-serif;
  text-rendering: optimizeLegibility;
  margin: 1rem;
  line-height: 1.5;
  padding-bottom: 2rem;
  background-attachment: fixed;
  background-image: url("data:image/svg+xml;charset=utf8,%3Csvg xmlns='http://www.w3.org/2000/svg'%3E%3Cdefs%3E%3Cfilter id='a'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='.4'/%3E%3C/filter%3E%3C/defs%3E%3Crect filter='url(%23a)' opacity='.3' width='100%25' height='100%25'/%3E%3C/svg%3E");

  min-height: 100%;
  color: var(--color);
  background-color: var(--bgColor);
}
main {
  max-width: 34rem;
  margin: 0 auto;
}
h1 {
  font-weight: 100;
  margin-top: 2rem;
  margin-bottom: 1rem;
  text-align: center;
}
h1 + p {
  font-size: 1.35rem;
  font-weight: 100;
  text-align: center;
}
a:link,
a:visited {
  color: var(--linkColor);
  text-decoration-color: var(--linkColorUnderline);
  outline: hsla(214, 71%, 80%, 0); solid .25rem;
  transition:
    color .3s ease-out,
    background-color .3s ease-out,
    outline-color .3s ease-out;
}
a:hover,
a:focus {
  color: var(--linkColorHover);
  outline: var(--linkBgHover) solid .25rem;
  background-color: var(--linkBgHover);
}
i {
  margin-right: .125em;
}

.-visually-hidden {
    position: absolute !important;
    clip: rect(1px,1px,1px,1px);
    padding: 0 !important;
    border: 0 !important;
    height: 1px !important;
    width: 1px !important;
    overflow: hidden;
}
.-nowrap {
    white-space: nowrap;
}

/* Not trying to redo my sites layout but a little neatness doesn't hurt */

.frm {
  background-color: var(--bgColorForm);
  border: 2px dashed #f90;
  padding: .6rem 1rem 1rem;
  max-width: 40rem;
  margin: 0 auto;
  line-height: 2;
}
.IN-fromFS {
  margin-right: 1rem;
}
.IN-toFS {
  margin-right: 1rem;
}
.frm_lbl > .lbl_txt {
  display: inline-block;
  min-width: 4rem;
}
.frm_set {
  border: 0;
}

[class^="IN_radio"] {
  margin-right: 1rem;
}

input[type="text"]:invalid + .validity:after {
  color: red;
  content: '✖';
}

input[type="text"]:valid + .validity:after {
  color: green;
  content: '✓';
}

.frm_set {
  display: inline-block;
}
              
            
!

JS

              
                var supportsES6 = (function() {
  // https://gist.github.com/bendc/d7f3dbc83d0f65ca0433caf90378cd95
  try {
    new Function('(a = 0) => a');
    return true;
  }
  catch (err) {
    return false;
  }
}());


console.clear();



// Restricts input for the given textbox to the given inputFilter function.
// https://stackoverflow.com/questions/469357/html-text-input-allow-only-numeric-input
function setInputFilter(textbox, inputFilter) {
  ["input", "keydown", "keyup", "mousedown", "mouseup", "select", "contextmenu", "drop"].forEach(function(event) {
    textbox.addEventListener(event, function() {
      if (inputFilter(this.value)) {
        this.oldValue = this.value;
        this.oldSelectionStart = this.selectionStart;
        this.oldSelectionEnd = this.selectionEnd;
      } else if (this.hasOwnProperty("oldValue")) {
        this.value = this.oldValue;
        this.setSelectionRange(this.oldSelectionStart, this.oldSelectionEnd);
      } else {
        this.value = "";
      }
    });
  });
}

// setInputFilter(document.getElementById("input"), function(value) {
//   return /^[-]?\d*\.?\d*$/.test(value); // Allow digits and '.' only, using a RegExp
// });


var Convert_Font_Sizes = (function (window, document, supportsES6) {

  'use strict';
  if (!supportsES6) return;


  const toUnit = document.querySelector('.IN_toUnit');
  const radiosFrom = document.querySelectorAll('.IN_radio-from');
  const radiosTo = document.querySelectorAll('.IN_radio-to');
  


  // Limit to four rounded decimal places.
  const sanitize = value => Math.round(value * 10000) / 10000;


  const setValue = (value, prop, valueWhenIllegal) => {
    value = sanitize(value);
    // if (isNaN(value) || value === 0)  value = valueWhenIllegal;
    if (isNaN(value))  value = valueWhenIllegal;
    inputs[prop].set(value); // string
  };


  const setInputEvents = prop => {

    const obj = inputs[prop].obj;

    obj.addEventListener('change', e => {
      setValue(e.target.value, prop, 1);
    });

    obj.addEventListener('input', e => {

      // Automatically updates valid values as they are typed

      const target = e.target;
      const value = target.value;
      const length = value.length;
      const lastChar = value.substr(length - 1);
      const firstChar = value.charAt(0);

      // Do not update values which detract from typing numbers
      // No update when:
      
      if (length === 0) return;
      // if (value === '0') return;
      if (lastChar === '.') return;
      if (lastChar === '-' && lastChar === firstChar) return;
      if (lastChar === '0' && value.indexOf('.') !== -1) return;
      
      setValue(value, prop, 1);

    });

    inputs[prop].set(inputs[prop].value);
  };


  const setInputValues = (prop, value) => {
    inputs[prop].obj.value = value;
    inputs[prop].value = value;
    updateResult();
  };


  const setRadioEvents = (radios, prop) => {
    for (const rad of radios) {
      rad.addEventListener('click', e => {
        inputs[prop].set(e.target.value);
      });
    }
  };


  const setRadioValues = (prop, value) => {
    inputs[prop].previousValue = inputs[prop].value;
    inputs[prop].value = value;
    if (toUnit) toUnit.textContent = inputs.unitsTo.value;
    updateResult();
  };


  const inputs = {

    rootFS : {
        obj : document.querySelector('.IN-rootFS'),
        value : 16,
        init : _ => setInputEvents('rootFS'),
        set : value => setInputValues('rootFS', value)
    },

    fromFS : {
        obj : document.querySelector('.IN-fromFS'),
        value : 16,
        init :  _ => setInputEvents('fromFS'),
        set : value => setInputValues('fromFS', value)
    },

    toFS : {
        obj : document.querySelector('.IN-toFS'),
        value : 1,
        init : _ => {},
        set : value => {
          // Prevents infinite recursion
          if (value !== parseFloat(inputs.toFS.obj.value)) {
            setInputValues('toFS', value);
          }
        }
    },

    unitsFrom : {
        value : 'rem',
        previousValue : 'rem',
        init : _ => setRadioEvents(radiosFrom, 'unitsFrom'),
        set : value => setRadioValues('unitsFrom', value)
    },

    unitsTo : {
        value : 'px',
        previousValue : 'px',
        init : _ => setRadioEvents(radiosTo, 'unitsTo'),
        set : value => setRadioValues('unitsTo', value)
    }

  };


  const updateResult = _ => {

    const from = inputs.fromFS.value;
    const root = inputs.rootFS.value;

    // Convert From value into pixels
    let pix = 0;
    switch(inputs.unitsFrom.value) {

      case 'px' :
        pix = from;
        break;
      case 'pt' :
        pix = from * 96 / 72;
        break;
      case 'percent' :
        pix = from * root / 100;
        break;
      case 'rem' :
        pix = from * root;
        break;

    }

    // Sets Result value
    switch (inputs.unitsTo.value) {

      case 'px' :
        pix = pix;
        break;
      case 'pt' :
        pix = pix * 72 / 96;
        break;
      case 'percent' :
        pix = pix * 100 / root;
        break;
      case 'rem' :
        pix = pix / root;
        break;
    }

    setValue(pix, 'toFS', 1);

  };

  // Open input settings and for each primary, run init

  const initialise = _ => {

    // Object.keys(inputs).forEach(key => inputs[key].init());

    Object.values(inputs).forEach(prop => prop.init());

    // Required to reset CSS ticks on page refresh
    const checked = document.querySelectorAll('[class^="IN_radio"]:checked');
    for (const chkd of checked) chkd.click();

  };

  initialise();

}(window, document, supportsES6));






// (Simulated) Update SVG calculator values (purely for the visual)

var Update_Svg_Calculator = (function (window, document, supportsES6) {

  'use strict';
  if (!supportsES6) return;

  const root_fs = document.querySelector('.IN-rootFS');
  const from_fs = document.querySelector('.IN-fromFS');
  const to_fs = document.querySelector('.IN-toFS');
  if (!(root_fs && from_fs && to_fs)) return;

  const radios = document.querySelectorAll('[class^="IN_radio-"]');
  if (!radios) return;

  // Limit to three rounded decimal places.
  const sanitize = value => Math.round(value * 1000) / 1000;

  const setSVG = _ => {

    const value = {
      from : from_fs.value,
      to : to_fs.value
    }

    const set = key => {

      const txtObj = document.getElementById('svg_' + key);
      if (!txtObj) return;

      const selector = `.IN_radio-${key}:checked`;
      const unitObj = document.querySelector(selector);
      if (!unitObj) return;

      const unit = unitObj.value === 'percent' ? '%' : unitObj.value;

      txtObj.textContent = sanitize(value[key]) + unit;
    }

    Object.keys(value).forEach(key => set(key));

  };


  const init = _ => {

    root_fs.addEventListener('input', setSVG);
    from_fs.addEventListener('input', setSVG);
    to_fs.addEventListener('input', setSVG);

    for (const rad of radios) {
      rad.addEventListener('click', setSVG);
    }

    setSVG();

  };


  init();

}(window, document, supportsES6));
              
            
!
999px

Console