Route calculator. Final solution

gistfile1.txt

function calculate(str){
let result = '';
let num = '';
let arrayOfElements = [];

if(/[^0-9\.\$\+\-\*]/.test(str)) {
    return '400: Bad request'; 
} else {
    for (let i = 0; i < str.length; i++) {
        if (str[i] === "$") {
            arrayOfElements.push(num);
            arrayOfElements.push(str[i]);
            num = '';
        } else if (str[i] === "*") {
            arrayOfElements.push(num);
            arrayOfElements.push(str[i]);
            num = '';
        } else if (str[i] === "-") {
            arrayOfElements.push(num);
            arrayOfElements.push(str[i]);
            num = '';
        } else if (str[i] === "+") {
            arrayOfElements.push(num);
            arrayOfElements.push(str[i]);
            num = '';
        } else if (i === str.length-1) {
            num = num + str[i];
            arrayOfElements.push(num);
        } else if (+str[i] === 0 || str[i] === ".") {
            num = num + str[i];
        } else if (+str[i] > 0 || str[i] === ".") {
            num = num + str[i];
        }
    }
}

function operations(array) {
  array.forEach((element, index) => {
      if (array[index] === "$") {
            result = result + (+array[index - 1] / +array[index + 1]);
            arrayOfElements.splice(index - 1, 3, result);
            result = '';
            operations(array);
        }
  });
    array.forEach((element, index) => {
        if (array[index] === "*") {
            result = result + (+array[index - 1] * +array[index + 1]);
            arrayOfElements.splice(index - 1, 3, result);
            result = '';
            operations(array);
        }
    });
    array.forEach((element, index) => {
        if (array[index] === "-") {
            result = result + (+array[index - 1] - +array[index + 1]);
            arrayOfElements.splice(index - 1, 3, result);
            result = '';
            operations(array);
        }
    });
    array.forEach((element, index) => {
        if (array[index] === "+") {
            result = result + (+array[index - 1] + +array[index + 1]);
            arrayOfElements.splice(index - 1, 3, result);
            result = '';
            operations(array);
        }
    })
}

operations(arrayOfElements);
return +arrayOfElements[0];
}