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

Are you asking to turn the math equation string into what it evaluates to? — di3
– di3, Commented Jan 29, 2022 at 17:49
There's nothing built into javascript for this, but various libraries are available. Or you can implement it yourself. — Bergi
– Bergi, Commented Jan 29, 2022 at 17:52

E.H. · Accepted Answer · 2022-01-31 05:39:28Z

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')"));

edited Jan 31, 2022 at 5:39

answered Jan 29, 2022 at 18:42

E.H.

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6 Comments

Infinite-3D Over a year ago

thanks, but it doesn't seem to be working completely. when i do checkAllowedCommands("(12)") or checkAllowedCommands("sin(10)"), it returns false. it seems like it doesn't work if the input starts or ends with ( or ).

E.H. Over a year ago

You were right. Splitting with the above RegEx added an empty string to the array and the empty string doesn't exist in the list of allowed commands. I added a filter after the split for non empty commands.

Infinite-3D Over a year ago

it still doesn't seem to work completely. addition and subtraction still doesn't work

E.H. Over a year ago

I thought you'd figure it out. You just need to add math operators to the following code: var commands = mathExpression.replace(/([()/*+-])/g, " $1 ").split(" ").filter(v => v);

Infinite-3D Over a year ago

one last thing- is there a way to make it work with scientific notation? something like 1e5 or 1e+5

|

garrettmills · Accepted Answer · 2022-01-29 18:26:27Z

1

Perhaps something like this package: https://www.npmjs.com/package/nerdamer

I've used Nerdamer in a few projects in the past, and it's pretty solid. Short of that, there's no "simple" way to do it short of implementing your own mini-parser that I know of.

answered Jan 29, 2022 at 18:26

garrettmills

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