JavaScript Validation API
Constraint Validation DOM Methods
Property | Description |
---|---|
checkValidity() | Returns true if an input element contains valid data. |
setCustomValidity() | Sets the validationMessage property of an input element. |
If an input field contains invalid data, display a message:
The checkValidity() Method
<input id="id1" type="number" min="100" max="300"
required>
<button onclick="myFunction()">OK</button>
<p id="demo"></p>
<script>
function myFunction() {
var inpObj = document.getElementById("id1");
if (!inpObj.checkValidity()) {
document.getElementById("demo").innerHTML = inpObj.validationMessage;
}
}
</script>
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Constraint Validation DOM Properties
Property | Description |
---|---|
validity | Contains boolean properties related to the validity of an input element. |
validationMessage | Contains the message a browser will display when the validity is false. |
willValidate | Indicates if an input element will be validated. |
Validity Properties
The validity property of an input element contains a number of properties related to the validity of data:
Property | Description |
---|---|
customError | Set to true, if a custom validity message is set. |
patternMismatch | Set to true, if an element's value does not match its pattern attribute. |
rangeOverflow | Set to true, if an element's value is greater than its max attribute. |
rangeUnderflow | Set to true, if an element's value is less than its min attribute. |
stepMismatch | Set to true, if an element's value is invalid per its step attribute. |
tooLong | Set to true, if an element's value exceeds its maxLength attribute. |
typeMismatch | Set to true, if an element's value is invalid per its type attribute. |
valueMissing | Set to true, if an element (with a required attribute) has no value. |
valid | Set to true, if an element's value is valid. |
Examples
If the number in an input field is greater than 100 (the input's max
attribute), display a message:
The rangeOverflow Property
<input id="id1" type="number" max="100">
<button onclick="myFunction()">OK</button>
<p id="demo"></p>
<script>
function myFunction() {
var txt = "";
if (document.getElementById("id1").validity.rangeOverflow) {
txt = "Value too large";
}
document.getElementById("demo").innerHTML = txt;
}
</script>
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If the number in an input field is less than 100 (the input's min
attribute), display a message:
The rangeUnderflow Property
<input id="id1" type="number" min="100">
<button onclick="myFunction()">OK</button>
<p id="demo"></p>
<script>
function myFunction() {
var txt = "";
if (document.getElementById("id1").validity.rangeUnderflow) {
txt = "Value too small";
}
document.getElementById("demo").innerHTML = txt;
}
</script>
Try it Yourself »