HTML attribute: pattern
The pattern
attribute specifies a regular expression the form control's value should match. If a non-null
value doesn't conform to the constraints set by the pattern
value, the ValidityState
object's read-only patternMismatch
property will be true.
Try it
Overview
The pattern
attribute is an attribute of the text, tel, email, url, password, and search input types.
The pattern
attribute, when specified, is a regular expression which the input's value
must match for the value to pass constraint validation. It must be a valid JavaScript regular expression, as used by the RegExp
type, and as documented in our guide on regular expressions.
The pattern's regular expression is compiled with the 'v'
flag. This makes the regular expression unicode-aware, and also changes how character classes are interpreted. This allows character class set intersection and subtraction operations, and in addition to ]
and \
, the following characters must be escaped using a \
backslash if they represent literal characters: (
, )
, [
, {
, }
, /
, -
, |
. Before mid-2023, the 'u'
flag was specified instead; If you're updating older code, this document outlines the differences.
The pattern's regular expression must match the entire input's value
, rather than matching a substring - as if a ^(?:
were implied at the start of the pattern and )$
at the end.
No forward slashes should be specified around the pattern text. No regular expression is applied if the attribute value is absent, an empty string, or invalid.
Some of the input types supporting the pattern attribute, notably the email and url input types, have expected value syntaxes that must be matched. If the pattern attribute isn't present, and the value doesn't match the expected syntax for that value type, the ValidityState
object's read-only typeMismatch
property will be true.
Constraint validation
If the input's value is not the empty string and the value does not match the entire regular expression, there is a constraint violation reported by the ValidityState
object's patternMismatch
property being true
.
Note: If the pattern
attribute is specified with no value, its value is implicitly the empty string. Thus, any non-empty input value
will result in constraint violation.
Usability and accessibility considerations
When including a pattern
, provide a description of the pattern in visible text near the control. Additionally, include a title
attribute which gives a description of the pattern. User agents may use the title contents during constraint validation to tell the user that the pattern is not matched. Some browsers show a tooltip with title contents, improving usability for sighted users. Additionally, assistive technology may read the title aloud when the control gains focus, but this should not be relied upon for accessibility.
Only relying on the title
attribute for the visual display of text content is discouraged, as many user agents do not expose the attribute in an accessible manner. Although some browsers show a tooltip when an element with a title is hovered, that leaves out keyboard-only and touch-only users. This is one of the several reasons you must include information informing users how to fill out the control to match the requirements.
While title
s are used by some browsers to populate error messaging, because browsers sometimes also show the title as text on hover, it therefore shows in non-error situations, so be careful not to word titles as if an error has occurred.
Examples
Matching a phone number
Given the following:
<p>
<label>
Enter your phone number in the format (123) - 456 - 7890 (<input
name="tel1"
type="tel"
pattern="[0-9]{3}"
placeholder="###"
aria-label="3-digit area code"
size="2" />) -
<input
name="tel2"
type="tel"
pattern="[0-9]{3}"
placeholder="###"
aria-label="3-digit prefix"
size="2" />
-
<input
name="tel3"
type="tel"
pattern="[0-9]{4}"
placeholder="####"
aria-label="4-digit number"
size="3" />
</label>
</p>
Here we have 3 sections for a north American phone number with an implicit label encompassing all three components of the phone number, expecting 3-digits, 3-digits and 4-digits respectively, as defined by the pattern
attribute set on each.
If the values are too long or too short, or contain characters that aren't digits, the patternMismatch
will be true. When true
, the element matches the :invalid
CSS pseudo-classes.
input:invalid {
border: red solid 3px;
}
If we had used minlength
and maxlength
attributes instead, we may have seen validityState.tooLong
or validityState.tooShort
being true.
Specifying a pattern
You can use the pattern
attribute to specify a regular expression that the inputted value must match in order to be considered valid (see Validating against a regular expression for a simple crash course on using regular expressions to validate inputs).
The example below restricts the value to 4-8 characters and requires that it contain only lower-case letters.
<form>
<div>
<label for="uname">Choose a username: </label>
<input
type="text"
id="uname"
name="name"
required
size="45"
pattern="[a-z]{4,8}"
title="4 to 8 lowercase letters" />
<span class="validity"></span>
<p>Usernames must be lowercase and 4-8 characters in length.</p>
</div>
<div>
<button>Submit</button>
</div>
</form>
This renders like so:
Specifications
Specification |
---|
HTML Standard # attr-input-pattern |
Browser compatibility
BCD tables only load in the browser