JSFiddle - React, Tailwind, and code Playground

author(s): Tao Xin

HTML

<script src="https://cdn.jsdelivr.net/gh/vanjs-org/van/public/van-0.12.4.nomodule.min.js"></script>

CSS

html { height: 100%; }

body {
  background-color: black;
  margin: 0;
  padding: 0;
  font-size: 10px;
  font-family: sans-serif;
  height: 100%;
}

@media (min-width: 400px) and (min-height: 400px) {
  html { font-size: 20px; }
}

@media (min-width: 500px) and (min-height: 500px) {
  html { font-size: 30px; }
}

@media (min-width: 600px) and (min-height: 600px) {
  html { font-size: 40px; }
}

@media (min-width: 800px) and (min-height: 800px) {
  html { font-size: 50px; }
}

#root {
  display: flex;
  flex-direction: column;
  flex-wrap: wrap;
  height: 100%;
}

#display {
  background-color: #858694;
  color: white;
  text-align: right;
  font-weight: 200;
  flex: 0 0 auto;
  width: 100%;
}

#display > div {
  font-size: 2.5rem;
  padding: 0.2rem 0.7rem 0.1rem 0.5rem;
}

#panel {
  background-color: #858694;
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  flex: 1 0 auto;
}

#panel > div {
  width: 100%;
  margin-bottom: 1px;
  flex: 1 0 auto;
  display: -ms-flexbox;
  display: flex;
}

.button {
  display: inline-flex;
  width: 25%;
  flex: 1 0 auto;
}

.button.wide { width: 50%; }

.button button {
  background-color: #e0e0e0;
  border: 0;
  font-size: 1.5rem;
  margin: 0 1px 0 0;
  flex: 1 0 auto;
  padding: 0;
}

.button:last-child button {
  margin-right: 0;
  background-color: #f5923e;
  color: white;
}

JavaScript

const {button, div} = van.tags

const Calculator = () => {
  const displayNum = van.state(0)
  let lhs = null, op = null, rhs = 0

  const calc = (lhs, op, rhs) => {
    const rhsNumber = parseFloat(rhs)
    if (!op || lhs === null) return rhsNumber
    if (op === "+") return lhs + rhsNumber
    if (op === "-") return lhs - rhsNumber
    if (op === "x") return lhs * rhsNumber
    if (op === "÷") return lhs / rhsNumber
  }

  const onclick = e => {
    const str = e.target.innerText
    if (str >= "0" && str <= "9") {
      if (rhs) {
        if (typeof rhs === "string") rhs += str; else rhs = rhs * 10 + parseInt(str)
      } else
        rhs = parseInt(str)
    } else if (str === "AC") {
      lhs = op = null, rhs = 0
    } else if (str === "+/-") {
      if (rhs) rhs = -rhs
    } else if (str === "%") {
      if (rhs) rhs *= 0.01
    } else if (str === "+" || str === "-" || str === "x" || str === "÷") {
      if (rhs !== null) lhs = calc(lhs, op, rhs), rhs = null
      op = str
    } else if (str === "=") {
      if (op && rhs !== null) lhs = calc(lhs, op, rhs), op = null, rhs = null
    } else if (str === ".") {
      rhs = rhs ? rhs + "." : "0."
    }

    displayNum.val = rhs ?? lhs
  }

  const Button = str => div({class: "button"}, button(str))

  return div({id: "root"},
    div({id: "display"}, div(displayNum)),
    div({id: "panel", onclick},
      div(Button("AC"), Button("+/-"), Button("%"), Button("÷")),
      div(Button("7"), Button("8"), Button("9"), Button("x")),
      div(Button("4"), Button("5"), Button("6"), Button("-")),
      div(Button("1"), Button("2"), Button("3"), Button("+")),
      div(div({class: "button wide"}, button("0")), Button("."), Button("=")),
    ),
  )
}

van.add(document.body, Calculator())