This Expression Evaluator is a powerful tool designed to calculate the result of mathematical expressions entered by the user. Unlike traditional calculators that often have fixed operations (like addition, subtraction, multiplication, division), an expression evaluator can interpret a wide range of mathematical formulas, including those with parentheses, various operators, and potentially functions, based on defined rules of mathematical precedence.
How it Works: The Math Behind the Scenes
At its core, evaluating an expression involves parsing the input string and applying the order of operations, commonly remembered by mnemonics like PEMDAS/BODMAS:
Parentheses / Brackets
Exponents / Orders (powers, square roots, etc.)
Multiplication and Division (from left to right)
Addition and Subtraction (from left to right)
Our calculator implements a simplified version focusing on basic arithmetic operators +, -, *, /, and parentheses (). The JavaScript `eval()` function is used internally for its ability to parse and compute such expressions directly. While powerful, it's important to be aware of the security implications of using `eval()` with untrusted user input in a production web application, as it can execute arbitrary JavaScript code. For this educational calculator, it serves as a straightforward way to demonstrate expression evaluation.
Mathematical Operators Supported:
Addition:+ (e.g., 5 + 3)
Subtraction:- (e.g., 10 - 4)
Multiplication:* (e.g., 6 * 7)
Division:/ (e.g., 20 / 5)
Parentheses:() (used to group operations and control order, e.g., (5 + 3) * 2)
Use Cases:
Quick Calculations: Performing complex calculations without needing to use a standard calculator interface step-by-step.
Programming Practice: Understanding how programming languages parse and execute mathematical statements.
Educational Tool: Helping students visualize the application of the order of operations.
Data Input Verification: Basic validation that a user-entered string can be interpreted as a valid mathematical expression.
Example Usage:
If you enter the expression (15 + 5) * 3 / 2 - 10, the calculator will perform the following steps (internally):
Addition/Subtraction (left to right):30 - 10 = 20.
The final result displayed would be 20.
function evaluateExpression() {
var expressionInput = document.getElementById("expression");
var resultDiv = document.getElementById("result");
var expression = expressionInput.value;
// Clear previous error messages
resultDiv.style.backgroundColor = "var(–success-green)";
resultDiv.style.color = "var(–text-light)";
if (!expression) {
resultDiv.textContent = "Please enter an expression.";
resultDiv.style.backgroundColor = "#dc3545″; // Red for error
return;
}
try {
// Basic validation to prevent execution of malicious code
// This is a very basic check and not foolproof security.
// For real-world applications, use a dedicated math parsing library.
var sanitizedExpression = expression.replace(/[^0-9+\-*/().\s]/g, ");
if (sanitizedExpression !== expression) {
throw new Error("Invalid characters in expression.");
}
// Check for unbalanced parentheses – a common source of errors
var parenBalance = 0;
for (var i = 0; i < expression.length; i++) {
if (expression[i] === '(') {
parenBalance++;
} else if (expression[i] === ')') {
parenBalance–;
}
if (parenBalance < 0) { // Closing parenthesis without an opening one
throw new Error("Mismatched parentheses.");
}
}
if (parenBalance !== 0) { // Unclosed opening parenthesis
throw new Error("Mismatched parentheses.");
}
// Additional check for invalid sequences like multiple operators
if (/[+\-*/]{2,}/.test(expression.replace(/\s/g, ''))) {
throw new Error("Invalid operator sequence.");
}
if (/\([^)]*$/.test(expression) || /^[^(]*\)/.test(expression)) {
throw new Error("Invalid parenthesis usage.");
}
// Using eval cautiously for demonstration purposes.
// In a production environment, a more secure parsing library is recommended.
var result = eval(expression);
// Check if the result is a valid number
if (typeof result === 'number' && isFinite(result)) {
resultDiv.textContent = result;
resultDiv.style.backgroundColor = "var(–success-green)";
} else {
// Handle cases where eval might return non-numeric or infinite results
throw new Error("Invalid expression result.");
}
} catch (error) {
resultDiv.textContent = "Error: " + error.message;
resultDiv.style.backgroundColor = "#dc3545"; // Red for error
resultDiv.style.color = "var(–text-light)";
}
}