textarea/input maxlength Parity
Measures an input or textarea API value in UTF-16 code units against maxlength. Supply the already-normalized API value; this does not model user-edit constraint-validation conditions or grapheme counts.
Description
HTML maxlength counts UTF-16 code units in a control’s API value.
HTML maxlength counts UTF-16 code units in a control’s API value. A displayed character can occupy multiple units, so visible character counts can differ.1
Measures an input or textarea API value in UTF-16 code units against maxlength. Supply the already-normalized API value; this does not model user-edit constraint-validation conditions or grapheme counts.
When to use textarea/input maxlength Parity
Use this for the following task: Measures an input or textarea API value in UTF-16 code units against maxlength. Supply the already-normalized API value; this does not model user-edit constraint-validation conditions or grapheme counts.
Prepare the parsed attribute values, element states or ordered local lists requested below. Keep attribute presence separate from value.
How to use textarea/input maxlength Parity and understand its results
- Prepare the parsed attribute values, element states or ordered local lists requested below. Keep attribute presence separate from value.
- Enter value, maxlength using the field table, then run the tool.
- Read codeUnits, withinLimit, excess. Interpret flags, units, ordering and placeholder values using the rules below.
- Review any reported issue or failed check, correct the supplied values when appropriate, and verify the result in its intended context.
| Input field | Meaning | Value type and bounds | Requirement |
|---|---|---|---|
| value | Value | string; maximum text length 100000 | Required |
| maxlength | Maxlength | integer; minimum 0 | Required |
Use the normalized input or textarea API value. Compare its JavaScript length with maxlength inclusively; return withinLimit and the nonnegative excess.2
codeUnits = value.length; excess = max(0, codeUnits − maxlength) This summarizes the declared operation. Units, indexing, inclusivity and exceptional cases are explained in the surrounding text.
| Output field | Meaning | Value type |
|---|---|---|
| codeUnits | Code Units | integer |
| withinLimit | Within Limit | boolean |
| excess | Excess | integer |
{
"input": {
"value": "A😀B",
"maxlength": 3
},
"output": {
"codeUnits": 4,
"withinLimit": false,
"excess": 1
}
}Limitations and assumptions
This does not count grapheme clusters or reproduce the user-edit conditions for browser constraint validation.
This evaluates supplied local information; it does not fetch a page or run a browser. Malformed requests produce input errors. A successfully evaluated request can still contain false flags, empty result lists or a result outside the supplied threshold; those outcomes have the meanings stated above.
Alternative or Complementary methods
Choose required/readonly/disabled Diff Table for this operation: Resolves required, readonly and disabled flags for an ordinary input type. Effective disabled includes inherited fieldset state supplied by the caller. Submission eligibility concerns disabling only; name, checkedness and submitter selection are separate. For a complementary task, use min/max/step Number Input Semantics for this operation: Checks parsed number-input min/max and step constraints using exact decimal arithmetic on the canonical decimal spelling of supplied finite numbers. Supply normalized positive step (default 1) and attribute presence flags; this is an ideal decimal model, independent of browser binary floating point tolerances.
Further background: HTML / accessibility reference: textarea/input maxlength Parity.
References
Similar or alternative tools
- required/readonly/disabled Diff Table
Resolves required, readonly and disabled flags for an ordinary input type. Effective disabled includes inherited fieldset state supplied by the caller. Submission eligibility concerns disabling only; name, checkedness and submitter selection are separate.
- min/max/step Number Input Semantics
Checks parsed number-input min/max and step constraints using exact decimal arithmetic on the canonical decimal spelling of supplied finite numbers. Supply normalized positive step (default 1) and attribute presence flags; this is an ideal decimal model, independent of browser binary floating point tolerances.