Danke. Habs jetzt mit einem Prof gelöst
Html: <div id="msg"></div>
<input id="txt_input"
type="input"
required
pattern="[0-9]+[\+\-\*\/]{1}[0-9]+"
placeholder="1 + 3"
title='Bitte im Format "Zahl Operant Zahl" eingeben :-)'></input>
<button id="btn_calculate">berechne</button>
<input id="txt_result" type="input" disabled></input>
JS: $("#btn_calculate").click( function() {
let string = $("#txt_input").val().trim();
let add = new RegExp("^[0-9]+[\+]{1}[0-9]+$").test(string);
let sub = new RegExp("^[0-9]+[\-]{1}[0-9]+$").test(string);
let mul = new RegExp("^[0-9]+[\*]{1}[0-9]+$").test(string);
let div = new RegExp("^[0-9]+[\/]{1}[0-9]+$").test(string);
if (add || sub || mul || div) {
let result = null;
if(add) {
let list_of_nums = string.split("+");
let z1 = parseInt(list_of_nums[0].trim());
let z2 = parseInt(list_of_nums[1].trim());
result = z1 + z2;
}
if(sub) {
let list_of_nums = string.split("-");
let z1 = parseInt(list_of_nums[0].trim());
let z2 = parseInt(list_of_nums[1].trim());
result = z1 - z2;
}
if(mul) {
let list_of_nums = string.split("*");
let z1 = parseInt(list_of_nums[0].trim());
let z2 = parseInt(list_of_nums[1].trim());
result = z1 * z2;
}
if(div) {
let list_of_nums = string.split("/");
let z1 = parseInt(list_of_nums[0].trim());
let z2 = parseInt(list_of_nums[1].trim());
result = z1 / z2;
}
$("#txt_result").val(result);
} else {
$("#txt_result").val("fail");