The Scientific Calculator UI Problem That Nobody Solves Well

Building a calculator in JavaScript is the classic beginner project. Building a good calculator that handles operator precedence negative numbers and edge cases correctly is surprisingly difficult. The operator precedence problem The simplest calculator implementation processes operations left to right: 2 + 3 * 4 = 20 (wrong) The correct answer is 14 because multiplication has higher precedence than addition. A proper calculator must implement operator precedence, which requires either the Shunting-Yard algorithm or recursive descent parsing. function evaluate ( expression ) { // Tokenize const tokens = expression . match ( / (\d + \.?\d *| [ + \- * / ^() ]) /g ); // Shunting-Yard algorithm const output = []; const operators = []; const precedence = { ' + ' : 1 , ' - ' : 1 , ' * ' : 2 , ' / ' : 2 , ' ^ ' : 3 }; for ( const token of tokens ) { if ( ! isNaN ( token )) { output . push ( parseFloat ( token )); } else if ( token === ' ( ' ) { operators . push ( token ); } else if ( token ==