Dynamically increasing font size

Question

I would like to increase the font size of the paragraph as well as the font size of the number in the button.

I copied and pasted my sizer function from StackOverflow (a few alterations) and thought it would work and still can't get it to work. Can someone help?

Since I've spent so much time on just the first part, as a beginner programmer, I'm wondering what I am missing. Does anyone have any ideas from my code or their experience as to what I might be missing?

Thanks as always.

<html>
    <button onclick='incrementer(); sizer()' id='count' value=0 />0</button>
    <p id='test'>a</p>
    <script>
      clicks = 0
        incrementer = function () {
          clicks += 1
          click = document.querySelector("#count").textContent = clicks;
          click.innerHTML = document.getElementById("count").value = document.getElementById('test');
    }
        sizer = function changeFontSize() {
    div = document.getElementById("test");
    currentFont = div.style.fontSize.replace("pt", "");

    div.style.fontSize = parseInt(currentFont) + parseInt(clicks) + "pt";
}
</script>
</html>

Have you tried to verify that both functions are actually called? For example via `console.log();`? — , Jul 20 '18 at 22:09

CodeF0x · Answer 1 · 2018-07-20T22:32:45.020

1

Some things here:

I woudn't append two functions to your onclick here. Just append one and call your second function from the first one that gets fired via onclick. That looks a lot more tidy
Don't forget to put var before every variable, without it's not valid JavaScript
I didn't quite understand what you tried with your currentFont variable, so I removed it. It's not necessary and causes the script to not working correctly

<html>
<button onclick='incrementer()' id='count' value=0 />0</button>
<p id='test'>a</p>
<script>
  var clicks = 0;
  var incrementer = function() {
    clicks += 1;
    var click = document.querySelector("#count").textContent = clicks;
    click.innerHTML = document.getElementById("count").value = document.getElementById('test');
    sizer();
  }
  var sizer = function changeFontSize() {
    var div = document.getElementById("test");

    div.style.fontSize = parseInt(clicks) + "pt";
  }
</script>

</html>

edited Jul 20 '18 at 22:32

answered Jul 20 '18 at 22:08

CodeF0x

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The `currentFont` allows him to start from a base-line font size, as opposed to starting from 1pt as in your example. – Mattkwish Jul 20 '18 at 22:19
Avoid var everywhere and use semicolons – Luca Jul 20 '18 at 22:31
1

@Luca Oh well, I actually stumpled upon some semicolons. Thank you for pointing out. – CodeF0x Jul 20 '18 at 22:33

Mattkwish · Answer 2 · 2018-07-20T22:22:16.047

You don't have an initial font-size style on your <p> tag, so it div.style.fontSize is always empty. Also, best practice is to always use var when introducing new variables in javascript.

One good trick to help debugging things like these is to use console.log() at various points, and see whats coming out in your browser console. I used console.log(div.style.fontSize) and the answer became clear.

Working below after adding <p style='font-size:12px'>a</p>:

<html>
    <button style='font-size:12px;' onclick='incrementer(); sizer()' id='count' value=0 />0</button>
    <p id='test' style='font-size:12px;'>a</p>
    <script>
      var clicks = 0
      incrementer = function () {
          clicks += 1
          click = document.querySelector("#count").textContent = clicks;
          click.innerHTML = document.getElementById("count").value = document.getElementById('test');
      }
      var sizer = function changeFontSize() {
          var div = document.getElementById("test");
          var btn = document.getElementById("count");
          var newSize = parseInt(div.style.fontSize.replace("pt", "")) + parseInt(clicks);
          div.style.fontSize = newSize + "pt";
          btn.style.fontSize = newSize + "pt";
      }
    </script>
</html>

score 0 · Answer 3 · answered Jul 20 '18 at 22:21

The issue here is that there is no initial value for the fontSize of your <p> tag so div.style.fontSize returns an empty string. You can use window.getComputedStyle instead of div.style.fontSize and you will get the current fontSize. There is already a post explaining this method

https://stackoverflow.com/a/15195345/7190518

score 0 · Answer 4 · answered Jul 20 '18 at 22:29

I don't understand the logic of this solution, but you can simplify it avoiding to use a lot of var (anyway always prefer let or const if you don't need to change), using a single function and writing less code.

function increment(e){
  const ctrl = document.getElementById('test');
  let current = parseInt(e.dataset.size);
  current += 1;
  e.innerHTML = current;
  e.dataset.size = current;
  ctrl.style.fontSize = current + 'pt';
}

<button onclick="increment(this);" data-size="20">20</button>
    <p id='test' style="font-size:20pt;">A</p>

score 0 · Accepted Answer · answered Jul 20 '18 at 22:33

Here's a from-scratch version that does what you're asking for. I'll point out a few things that I did to help you out.

https://codepen.io/anon/pen/VBPpZL?editors=1010

<html>
  <body>
    <button id="count">0</button>
    <p id="test">
      Lorem Ipsum is simply dummy text of the printing and typesetting industry.
    </p>    
  </body>
</html>

JS:

window.addEventListener('load', () => {
  const button = document.querySelector('#count');
  const paragraph = document.querySelector('#test');
  const startingFontSize = window.getComputedStyle(document.body, null)
    .getPropertyValue('font-size')
    .slice(0, 2) * 1;
  let clicks = 0;

  button.addEventListener('click', () => {
    clicks++;

    // this is a template literal 
    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals
    const fontSize = `${startingFontSize + clicks}px`;

    button.innerHTML = clicks;  
    button.style.fontSize = fontSize;
    paragraph.style.fontSize = fontSize;
  });
});

The code runs when the page is loaded, so we attach an event listener on the window object listening for the load event.

We then store references to the button and the paragraph elements. These are const variables because their values won't change. This also limits their scope to the containing function.

We get the initial font size for the body element, because in this example we aren't explicitly setting a base font in css so we're just using the one for the document. getComputedStyle is a somewhat expensive operation, and in this case we only need to get it in the beginning because it won't change, so we also store it as a const. The value is returned as a string like "16px" but we need the number, hence the slice and multiplying by one to cast the string into a number. parseInt would also do the same thing.

Notice that clicks is defined with let. This means that the variable can be changed. var still works of course, but in modern practices its best to use const and let when declaring variables. This is partly because it forces you to think about what kind of data you're working with.

We add an event listener to the button element and listen for the click event. First, we increment the clicks variable. Then we declare fontSize using a template literal which adds our new clicks count to the startingFontSize and "px" to get a string.

Finally, the innerHTML value of the button element is updated. Then we update the fontStyle property for both elements.

Dynamically increasing font size

5 Answers5