By the end of this tutorial, you’ll confidently use Lodash’s _.lowerFirst() method in real JavaScript projects.
Call _.lowerFirst(string) for camelCase.
Rest of string unchanged.
Convert PascalCase to camelCase.
Normalize object property names.
Single char vs full string.
Round-trip casing helpers.
_.lowerFirst()?It lowercases the first character of a string and leaves all other characters unchanged.
Import only what you need: import lowerFirst from "lodash/lowerFirst" keeps bundles small.
_.lowerFirst([string=''])import lowerFirst from "lodash/lowerFirst";
const original = "HelloWorld";
const result = lowerFirst(original);
console.log(result);
// -> "helloWorld"| Task | Code pattern | Result |
|---|---|---|
| PascalCase fix | _.lowerFirst('HelloWorld') | helloWorld |
| Label to key | _.lowerFirst('UserName') | userName |
| Map object keys | _.mapKeys(obj, (_, k) => _.lowerFirst(k)) | camelCase keys |
| Array of names | names.map(_.lowerFirst) | Batch convert |
| Opposite | _.upperFirst(str) | HelloWorld |
| Full lower | _.lowerCase(str) | hello world |
NoReturns new string
First charRest unchanged
camelCaseJS identifiers
_.upperFirst()Capitalize first
Every argument to _.lowerFirst() and what it controls:
stringOptionalThe string to transform. When omitted or empty, returns an empty string.
_.lowerFirst('HelloWorld')return valueNew stringFirst character lowercased; all following characters unchanged. The original string is not mutated.
// -> 'helloWorld'scopeImportantOnly index 0 is modified. Internal capitals like jOhN stay as-is after the first character.
_.lowerFirst('jOhN')pair withmapKeysCombine with _.mapKeys to rename PascalCase API keys to camelCase in one pass.
_.mapKeys(obj, (_, k) => _.lowerFirst(k))For spaced lowercase words, use _.lowerCase(). For full identifier restructuring, use _.camelCase().
Practical _.lowerFirst() patterns with copy-ready code and interactive Try It Yourself labs.
Lowercase the first character while preserving the rest.
Convert a capitalized identifier to camelCase style.
const original = "HelloWorld";
const result = _.lowerFirst(original);
console.log(result);
// -> "helloWorld"Only H changes; elloWorld stays the same.
Format labels, user input, and object keys.
Turn a label-style name into a camelCase object key.
const label = "UserName";
const key = _.lowerFirst(label);
console.log(key);
// -> "userName"Common when mapping UI labels to JavaScript property names.
Convert PascalCase keys from an external API to camelCase.
const requestData = {
UserName: "john_doe",
EmailAddress: "john@example.com"
};
const formatted = _.mapKeys(requestData, (_, key) =>
_.lowerFirst(key)
);
console.log(formatted);
// -> { userName: "john_doe", emailAddress: "john@example.com" }Combine with _.mapKeys to reshape objects in one step.
Apply lowerFirst to every item in an array of field names.
const fields = ["FirstName", "LastName", "EmailAddress"];
const camelFields = fields.map(_.lowerFirst);
console.log(camelFields);
// -> ["firstName", "lastName", "emailAddress"]Pass _.lowerFirst directly as a callback to map.
Edge cases and comparison with related helpers.
Strings that already start lowercase are returned effectively unchanged.
const input = "jOhN";
const result = _.lowerFirst(input);
console.log(result);
// -> "jOhN" (first char already lower)Only the first character is considered; other capitals remain.
See lowerFirst and upperFirst as inverse first-character operations.
import lowerFirst from "lodash/lowerFirst";
import upperFirst from "lodash/upperFirst";
const camel = "helloWorld";
const pascal = "HelloWorld";
console.log(upperFirst(camel)); // -> "HelloWorld"
console.log(lowerFirst(pascal)); // -> "helloWorld"
// Round-trip:
console.log(lowerFirst(upperFirst(camel))); // -> "helloWorld"Use together when normalizing identifiers from different sources.
_.lowerFirst() WorksLodash coerces null/undefined to empty string.
Only the initial code unit is targeted.
Uppercase first letter becomes lowercase.
Original tail is appended unchanged.
_.lowerFirst() affects only the first character._.lowerFirst() is the precise tool when you need camelCase identifiers from PascalCase names—only the first letter changes, so UserName becomes userName without touching internal capitals.
For full string restructuring or search normalization, use _.camelCase() or _.lowerCase() instead.
_.lowerFirst()One char changes.
BasicsJS identifiers.
PatternAPI normalization.
ObjectFull string style.
CompareOpposite helper.
Related_.lowerFirst() is the inverse of _.upperFirst()—both touch only the first character. For full camelCase from arbitrary strings (with word splitting), use _.camelCase() instead.
Open the Try It editor and run the examples with your own input.
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