JSFiddle - React, Tailwind, and code Playground

by Boris Šuška

HTML

<input id="calcIn" value="Tan(25)"/>

JavaScript

input = document.getElementById('calcIn');
equation = true;
tan = true;

if (equation) {
    if (tan == true) {
        if (input.value.indexOf('Tan(') == 0) {
            inputVal = input.value;
            inputVal = inputVal.replace('Tan(', '');
            inputVal = inputVal.replace(')', '');
            input.value = Math.tan(inputVal);
        } else {
            input.value = 'Syntax Error';
            tan = false;
        }
    }
    else {
        input.value = eval(equation);
    }
}