function checkAgeNotNegative() {
const myElement = document.getElementById('age');
const age = myElement.value;
if(age < 0) {
showMessage('Alter kann nicht negativ sein.');
}
}
function checkAgeIsNumber() {
const myElement = document.getElementById('age');
const age = myElement.value;
if(!(!isNaN(parseFloat(age)) && isFinite(age))) {
showMessage('Alter muss Zahl sein.');
}
}
function clearMessage() {
showMessage('');
}
function showMessage(message) {
const output = document.getElementById('output');
output.textContent = message;
}
function init() {
const myElement = document.getElementById('age');
myElement.addEventListener(
'blur',
clearMessage
);
myElement.addEventListener(
'blur',
checkAgeNotNegative
);
myElement.addEventListener(
'blur',
checkAgeIsNumber
);
}
document.addEventListener("DOMContentLoaded", init);