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a bunch of vanilla JS practice projects based on JavaScript 30 by WesBos.

03-font adjuster

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Change the value of CSS properties

We create one CSS variable for each of all the properties we want to adjust.

:root {
 --font-size: 20px;
 --line-heigh: 25px;
 --word-spacing: 1px;
 --letter-spacing: 1px;

.div_textBox {
 width: 50%;
 border: 2px solid black;
 padding: 1rem;
 font-size: var(--font-size);
 line-height: var(--line-height);
 word-spacing: var(--word-spacing);
 letter-spacing: var(--letter-spacing);

Get input from range slider

In HTML, every range slider has an attribute name with the CSS property as its value.

<div class="div_valueBox">
 <input type="range" min="1" max="50" value="20" name="font-size" class="input" />
 <div class="div_value">
  font size: <span class="span_fontSize">20</span>px

In JavaScript, we listen for an input event on each slider.

const inputs = document.querySelectorAll(".div_valueBox input");

function handleUpdate() {`--${}`, this.value + "px");
//For example,
//<input type="range" min="1" max="50" value="20" name="font-size" class="input" />
//in this case will set --font-size to 20

inputs.forEach(input => input.addEventListener("input", handleUpdate));

Change the display value

Whenever there is an input, we update the content in the span.

const span_fontSize = document.querySelector(".span_fontSize");
const span_lineHeight = document.querySelector(".span_lineHeight");
const span_wordSpacing = document.querySelector(".span_wordSpacing");
const span_letterSpacing = document.querySelector(".span_letterSpacing");

function outputValue() {
 switch ( {
  case "font-size":
   span_fontSize.textContent = this.value;
  case "line-height":
   span_lineHeight.textContent = this.value;
  case "word-spacing":
   span_wordSpacing.textContent = this.value;
  case "letter-spacing":
   span_letterSpacing.textContent = this.value;

inputs.forEach(input => input.addEventListener("input", outputValue));