Clean user input
Normalize form fields such as usernames or display names before validation and storage.
Zod · Module
.trim
z.string().trim() creates a string schema that removes surrounding whitespace from parsed values. It is a built-in string transformation that can be chained with other string checks and transforms.
How it works
.trim() is a string transformation in Zod. It removes surrounding whitespace from an input string and returns the trimmed value, so subsequent string checks operate on the transformed result.
Syntax
z.string().trim()Returns
A string with surrounding whitespace removed.
Key points
- Call
.trim()onz.string()to remove surrounding whitespace during parsing. - Zod documents
.trim()as a mutating transform, meaning the parsed output is changed. - When used through a codec, decoding a padded string returns the trimmed string.
- The documented codec example also shows encoding a padded string produces the trimmed value.
.trim()is one of several built-in string transformations available alongside casing and Unicode normalization methods.
Common mistakes
.trim()transforms the parsed value; it is not merely a validation check.
Example: Trim a username
import { z } from "zod";
const username = z.string().trim().min(1);
console.log(username.parse(" ada ")); // "ada"The schema removes surrounding whitespace before applying the non-empty constraint.
When to use it
Reject blank values
Ensure whitespace-only input fails a following .min(1) constraint.
Canonicalize text
Prepare values for downstream comparisons where accidental surrounding spaces should not matter.
Interview questions
QWhat does z.string().trim() do?
It is declared as z.string().trim(). Parsing a string such as " hello " produces "hello", because the transform removes surrounding whitespace.
Follow-up: How would you make the trimmed result non-empty? Chain a constraint after the transform, for example z.string().trim().min(1).
QWhat type of input does .trim() handle?
It belongs on a string schema, so the input must first satisfy z.string(). After parsing, the output is the whitespace-trimmed string.
Follow-up: How can preprocessing accept nullable input? Use z.preprocess to call .trim() conditionally, then validate the resulting value with z.string().
QWhere does .trim() fit in a Zod string pipeline?
.trim() can be combined with other string methods in a schema chain. For example, trimming before .min(1) ensures the length check sees the normalized value.
Follow-up: What is the difference between trimming and lowercasing? Trimming removes surrounding whitespace, while toLowerCase() changes letter casing.
Related
z.string()z.string().toLowerCase()z.string().toUpperCase()z.string().normalize()z.preprocess