ValidityState: badInput property

The read-only badInput property of the ValidityState interface indicates if the user has provided input that the browser is unable to convert. For example, if you have a number input element whose content is a string.

Value

A boolean that is true if the ValidityState object does not conform to the expected type.

Examples

Detecting bad input

The following example checks the validity of a numeric input element. If the user enters text instead of a number, the element fails constraint validation, and the styles matching input:invalid are applied. The <pre> element above the input shows the validation message when the element badInput evaluates to true:

css

input:invalid {
 outline: red solid 3px;
}

body {
 margin: 0.5rem;
}
pre {
 padding: 1rem;
 height: 2rem;
 background-color: lightgrey;
 outline: 1px solid grey;
}

html

<pre id="log">Validation logged here...</pre>
<input type="number" id="age" />

const userInput = document.getElementById("age");
const logElement = document.getElementById("log");

function log(text) {
 logElement.innerText = text;
}

userInput.addEventListener("input", () => {
 userInput.reportValidity();
 if (userInput.validity.badInput) {
 log(`Bad input detected: ${userInput.validationMessage}`);
 }
});