JavaScript — write a function that can solve a math [removed]without eval)

Question

Ultimately I want to take this:

2x + 3 = 5

and solve for x, by first subtract 3 from both sides so 2x = 2, then divide both si

Answer 1

You can do that in following steps:

• First of all use split() and split by the + and - which will occur after multiplication and division.
• Then use map() on array and split() it again by * and /.
• Now we have a function which will which will evaluate an array of numbers with operators to single number.
• Pass the nested array to complete multiplication and division.
• Then pass that result again to sovleSingle and perform addition and subtraction.

The function works same as eval as long as there are no brackets ().

Note: This doesnot matters the which occurs first among + and - or which occurs first among * and /. But *,/ should occur before +,-

function solveSingle(arr){
  arr = arr.slice();
  while(arr.length-1){
    if(arr[1] === '*') arr[0] = arr[0] * arr[2]
    if(arr[1] === '-') arr[0] = arr[0] - arr[2]
    if(arr[1] === '+') arr[0] = +arr[0] + (+arr[2])
    if(arr[1] === '/') arr[0] = arr[0] / arr[2]
    arr.splice(1,1);
    arr.splice(1,1);
  }
  return arr[0];
}

function solve(eq) {
  let res = eq.split(/(\+|-)/g).map(x => x.trim().split(/(\*|\/)/g).map(a => a.trim()));
  res = res.map(x => solveSingle(x)); //evaluating nested * and  / operations.
   
  return solveSingle(res) //at last evaluating + and -
  
  
}

console.log(solve("3 - 6 * 3 / 9 + 5")); //6
console.log(eval("3 - 6 * 3 / 9 + 5")) //6