Allow math problems in string input (JavaScript)

Question

Is there a way to parse math equations as input using JavaScript?

for example, when a user enters "10-25" as input, it is parsed to -15

I tried using eval, which works, but it allows users to run all JavaScript code, not just math equations.

If it's possible, I'd like to also allow some functions, like sin(), cos(), and degreesToRadians(), but not all functions.

examples

"5" //returns 5
"12-20" //returns -8
"3/2" //returns 1.5
"sin(3.14)" //returns 0.00159265292
"sin(degreesToRadians(180/2)) * 10" //returns 10

"alert('hi')" //doesn't work

Answer 1

You can split expression by math operations and check them.

Next code does it for: ( ) / *

mathExpression.replace(/([()/*])/g, " $1 ").split(" ").filter(v => v);

var allowedCommands = ["(", ")", /^\d*\.?\d*e?$/, "*", "/", "+", "-", "sin", "cos", "degreesToRadians"];

function checkCommand(arg) {
  return allowedCommands.some(v => {
    if (v instanceof RegExp) {
      return v.test(arg)
    } else {
      return v == arg;
    }
  });
}

function checkAllowedCommands(mathExpression) {
  var commands = mathExpression.replace(/([()/*+-])/g, " $1 ").split(" ").filter(v => v);
  var filterNotAllowedCommands = commands.filter(v => !checkCommand(v));
  return filterNotAllowedCommands.length == 0;
}


console.log(checkCommand("degreesToRadians"));
console.log(checkCommand("234"));

console.info("right expression");
console.info(checkAllowedCommands("sin(degreesToRadians(180/2)) * 10"));
console.info(checkAllowedCommands("(1.2e-6)"))
console.info(checkAllowedCommands("sin(1+2)"));

console.warn("wong expression");
console.info(checkAllowedCommands("alert('hi')"));