```
---
## 2️ JavaScript (`calc.js`)
```js
// Grab DOM elements
const display = document.getElementById('display');
const buttons = document.querySelectorAll('.grid button');
// ---------- Utility helpers ----------
function degToRad(d) { return d * Math.PI / 180; }
function radToDeg(r) { return r * 180 / Math.PI; }
// Factorial (integer only)
function factorial(n){
if (n < 0) throw new Error('Negative factorial');
if (n === 0 || n === 1) return 1;
let res = 1;
for(let i=2;i<=n;i++) res *= i;
return res;
}
// ---------- Build expression ----------
let expr = ''; // current expression string
// Add a token to the expression
function appendToken(token){
if (token === 'C') { // clear last entry
expr = expr.slice(0, -1);
} else if (token === 'AC'){
expr = '';
} else {
expr += token;
}
display.value = expr || '0';
}
// ---------- Evaluate ----------
function evaluate(){
try{
// Replace custom functions with Math equivalents
let e = expr;
// 10**x → 10^x
e = e.replace(/10\*\*/g, 'Math.pow(10,');
// x**y → Math.pow(x,y)
e = e.replace(/\*\*([\d\.]+)/g, (m,p)=>`),${p})`);
// Factorial
e = e.replace(/fact\(([^)]+)\)/g,(m,v)=>factorial(eval(v)));
// Trig functions (degrees → radians)
const trigFuncs = ['sin','cos','tan','asin','acos','atan'];
trigFuncs.forEach(f=>{
const re = new RegExp(`${f}\\(([^)]+)\\)`, 'g');
e = e.replace(re,(m,v)=>{
let val = eval(v);
if (['sin','cos','tan'].includes(f)){
return `Math.${f}(${degToRad(val)})`;
}else{
// inverse trig – output degrees
const rad = Math[`${f}`](val);
return `${radToDeg(rad)}`;
}
});
});
// log10 → Math.log10 or Math.log(x)/Math.LN10
e = e.replace(/log10\(([^)]+)\)/g,(m,v)=>`Math.log(${v})/Math.LN10`);
// ln → Math.log
e = e.replace(/ln\(([^)]+)\)/g,(m,v)=>`Math.log(${v})`);
// sqrt → Math.sqrt
e = e.replace(/sqrt\(([^)]+)\)/g,(m,v)=>`Math.sqrt(${v})`);
// abs → Math.abs
e = e.replace(/abs\(([^)]+)\)/g,(m,v)=>`Math.abs(${v})`);
// Evaluate the final expression
const result = eval(e);
display.value = result;
expr = '' + result; // allow chaining
}catch(err){
display.value = 'Error';
expr = '';
}
}
// ---------- Event listeners ----------
buttons.forEach(btn=>{
btn.addEventListener('click',()=>{
const val = btn.dataset.value || btn.textContent;
if (btn.id === 'equals'){
evaluate();
}else{
appendToken(val);
}
});
});
```
### How it works
1. **UI** – a grid of buttons, each with either `data-value` or an ID (`ac`, `c`, `equals`).
2. **Expression building** – clicking any button appends its token to the string that’s displayed.
3. **Evaluation** – when “=” is pressed, the string is parsed:
* Custom functions (`sin(`, `cos(` …) are translated into `Math` calls.
* Trigonometric inputs are treated in **degrees**; inverse trig outputs are also converted back to degrees for user‑friendly display.
* Factorial is implemented manually because JavaScript has no native operator.
4. The result replaces the current expression so you can continue working.
---
### Quick test
Save the two files above (`index.html` and `calc.js`) in the same folder, open `index.html` in a browser and try:
```
AC
7 8 9 ×
√
=
sin(30)
cos(60)
tan(45)
log10(1000)
ln(e)
fact(5)
10**3
2 ** 8
abs(-42)
```
All should compute correctly, giving you a lightweight but fully‑featured scientific calculator written purely in JavaScript. Happy calculating!