Use of Eval. Is there any alternative in this case?

Question

I came across the functionalities of eval() and I started using, but I learned about the risk in using eval() next to a input external.

I use the eval() to receive from a input-text to string which corresponds to a polynomial function. It was the most practical short-term alternative that I managed to pass a user data as variables and mathematical operations.

Are there risks in hosting a code with this function in the future? Is there an alternative to the eval() in that capacity?

function inserirLinhaTabela() 
{

    //Cálculo numérico: 

    var poli = document.getElementById("fx").value;
    var troca = 
    {
        sen: "Math.sin",
        cos: "Math.cos",
        e: "Math.E",
        ln: "Math.log",  
    }

    poli = poli.replace(/sen|cos|e|ln/gi, function(matched){
      return troca[matched];
    });

    function fdex(x)
    {
        return eval(poli);
    }

Answer 1

If I understood anything at all:

var funcoes = {
    sen: Math.sin,
    cos: Math.cos,
    e: Math.E,
    ln: Math.log,  
}
var funcao = "sen";
console.log(funcoes[funcao](30));

I put in the Github for future reference.

Instead of using texts I took the same functions and just called them without needing the eval(). A rough summary of eval() is to remove the quotation marks from a text and execute what was inside, so why not remove the quotation marks in your code?

I think it answers the rest of the question: Eval is either good or bad?.

Note that to catch general expressions you will have to make one parser the same way, and then you can use a slightly different form of this, the answer was on top of the presented code and not the whole context that later I saw that already existed in another question of the AP.