How to add math function without eval to basic calculator

Per the Odin Project's instructions, I need to make my basic calculator operate via math functions rather than using eval(). https://www.theodinproject.com/lessons/foundations-calculator

I've only added the addition part to my mathWorks function. However, I'm not sure how to tie my mathWorks function to my else if block when "=" is selected. Any help would be greatly appreciated.

const container = document.querySelector(".container");
const calcBody = document.querySelector("#calcBody");
const input = document.querySelector("#input");
let a = "";
let b = "";
let operator = "";
let result = "";


      
const numbers = {
    reset: "CE",
    goBack: "C",
    divide: "/",
    multiply: "*",
    seven: 7,
    eight: 8,
    nine: 9,
    add: "+",
    four: 4,
    five: 5,
    six: 6,
    minus: "-",
    one: 1,
    two: 2,
    three: 3,
    decimal: ".",
    zero: 0,
    equal: "=",
};

for (let key in numbers) {
    let button = document.createElement("button");
    button.setAttribute("id", key);
    button.textContent = numbers[key];
    container.appendChild(button);

    button.addEventListener("click", (e) => {
        let val = e.target.textContent;
       
        if(e.target.textContent === "+" || 
           e.target.textContent === "/" ||
           e.target.textContent === "*")
           {
           operator = val;
           input.textContent = a + " " + operator + " ";
           }

        else if(e.target.textContent === "CE") {
             input.textContent = "";
             a = "";
        }
        else if(input.textContent.includes("*") ||
                 input.textContent.includes("+")  ||
                 input.textContent.includes("/")) {
            b += val;
            input.textContent = a + " " + operator + " " + b;
        }

        else if(e.target.textContent === "="){
            mathWorks();
            }
        
        
            else 
        {
            a += val
            input.textContent = a;
        }

    });

    function mathWorks(){
        if(operator === "+"){
            result = parseFloat(a) + parseFloat(b);
            input.textContent = result;
            
        }

    }

}

I'm kind of at a loss at the moment. I've tried adding parseFloat and including a and b in mathWorks parameters.

In general, the training tasks for creating a calculator are reduced to more branching and creating functions for all mathematical operators.

If you can use function constructors, then the calculator might look like this:

const container = document.querySelector(".container");
const calcBody = document.querySelector("#calcBody");
const input = document.querySelector("#input");
let a = "";
let b = "";
let operator = "";
let result = "";

const numbers = {
  reset: "CE",
  goBack: "C",
  divide: "/",
  multiply: "*",
  seven: 7,
  eight: 8,
  nine: 9,
  add: "+",
  four: 4,
  five: 5,
  six: 6,
  minus: "-",
  one: 1,
  two: 2,
  three: 3,
  decimal: ".",
  zero: 0,
  equal: "=",
};

const actions = [];
let numAcc = '';
for (let key in numbers) {
  let button = document.createElement("button");
  button.setAttribute("id", key);
  button.textContent = numbers[key];
  container.appendChild(button);

  function clear() {
    input.textContent = "";
    actions.length = 0;
    numAcc = '';
  }

  button.addEventListener("click", (e) => {
    if (e.target.textContent === "CE") {
      clear();
      calcBody.textContent = '';
      return;
    }
    if (e.target.textContent === "C") {
      if (numAcc.length > 0) {
        numAcc = numAcc.slice(0, -1);
      } else {
        actions.pop();
        if (actions.length) {
          numAcc = actions[actions.length - 1];
          actions.pop();
        }
      }
      input.textContent = actions.join(' ') + ' ' + numAcc;
      return;
    }
    if (e.target.textContent === '=') {
      if (numAcc.length < 1 || actions.length < 2) {
        clear();
        calcBody.textContent = '';
      } else {
        const fn = new Function(`return ${actions.join(' ')} ${numAcc} + 0`);
        calcBody.textContent = fn();
        clear();
      }
    } else {
      if (e.target.textContent === '.' || !isNaN(e.target.textContent)) {
        numAcc += e.target.textContent;
      } else {
        if (numAcc.length) {
          actions.push(numAcc);
          actions.push(e.target.textContent);
          numAcc = '';
        } else {
          actions.pop()
          actions.push(e.target.textContent)
        }
      }
      input.textContent = actions.join(' ') + ' ' + numAcc;
    }
  });
}

<div class="container"></div>
<div id="input"></div>
<div id="calcBody"></div>