Normalize case
Canonicalizing user-entered identifiers or labels before storage or comparison.
Zod · Module
.toUpperCase
.toUpperCase() transforms parsed strings to uppercase. It takes no arguments and can be chained with other string transformations such as .trim().
How it works
.toUpperCase() is a string schema transformation that converts a successfully parsed string to uppercase. It can be chained with other string transformations such as .trim(); the resulting schema still represents a string.
Syntax
z.string().toUpperCase()Returns
A Zod string schema that uppercases parsed string values.
Key points
- Call
.toUpperCase()on a string schema to create an uppercase-normalizing parser. - The method can be chained after
.trim()when whitespace should be removed before uppercasing. - When used in the documented chain with
.prefault(" tuna "), parsing undefined yields the normalized value"TUNA". .toUpperCase()appears among string transformations, alongside Unicode normalization and case conversion helpers.- The current implementation category indicates that overwrite-based string transformations do not change the inferred type.
Common mistakes
- In current Zod, these methods are implemented through
.overwrite(), so they preserve the schema's inferred string type rather than creating a different output type.
Example: Normalize a string to uppercase
import { z } from "zod";
const schema = z.string().trim().toUpperCase();
console.log(schema.parse(" tuna ")); // "TUNA"Trims surrounding whitespace, then converts the parsed string to uppercase.
When to use it
Clean and uppercase input
Combining whitespace cleanup and case conversion in an input pipeline.
Preserve string typing
Applying a string transformation while retaining a string schema type.
Interview questions
QWhat does .toUpperCase() do?
It is called on a z.string() schema and uppercases the string during parsing. For example, z.string().toUpperCase().parse("hello") produces "HELLO".
Follow-up: How would you normalize both whitespace and case? Chain the transformations: z.string().trim().toUpperCase().
QWhen is the transformation applied?
It is a transformation method listed alongside .trim(), .toLowerCase(), and .normalize(). The input must first satisfy the string schema, after which the uppercase conversion is applied.
Follow-up: What happens if the input is not a string? The base z.string() schema rejects it before the string transformation can run.
QWhat is the method signature and output type?
The method takes no argument: z.string().toUpperCase(). Its parsed result remains a string, with lowercase letters converted to uppercase.
Follow-up: How can the operation be combined with a default-like preprocessing flow? Chain it with other documented schema methods, such as .trim() and .prefault().
Related
z.stringtrimtoLowerCasenormalizeprefaultoverwrite