By the end of this tutorial, you’ll use Lodash’s _.defaultTo() to supply fallbacks when values are null or undefined—without accidentally wiping out 0 or empty strings.
_.defaultTo(value, fallback) in one call.
Replaces null and undefined—not all falsy values.
Zero and empty string stay intact.
Fill missing API and app settings safely.
Pick the right fallback operator.
Single value vs object merge helper.
_.defaultTo()?_.defaultTo() is a Lodash util helper that returns a fallback value only when the first argument is null or undefined. Otherwise it returns the original value unchanged. It is the Lodash expression of nullish coalescing—cleaner than writing value != null ? value : fallback repeatedly in config loaders and data mappers.
_.defaultTo("", "guest") returns "", not "guest". An empty string is a deliberate value (user cleared the field). Only use || if you truly want to replace empty strings too.
Reach for _.defaultTo() when optional properties from JSON, query strings, or database rows may be absent, but legitimate falsy values like 0 or false should survive.
Pass the value to test and the fallback to use when it is nullish:
_.defaultTo(value, defaultValue)value — the value you have (may be null or undefined).defaultValue — returned only when value is null or undefined.0, "", false, and NaN are not replaced.value or defaultValue (not a function).value ?? defaultValue behaves the same way.import defaultTo from "lodash/defaultTo";
const name = defaultTo(undefined, "Guest");
// -> "Guest"
const count = defaultTo(0, 10);
// -> 0 (zero is kept)| Input value | _.defaultTo(v, "fb") | v || "fb" |
|---|---|---|
undefined | "fb" | "fb" |
null | "fb" | "fb" |
"" | "" | "fb" |
0 | 0 | "fb" |
false | false | "fb" |
"Ada" | "Ada" | "Ada" |
null | undefinedNullish only
??Same behavior
_.defaultsDifferent helper
UtilValue fallback
Arguments to _.defaultTo() and what each controls:
value RequiredThe value to return when it is defined (including empty string, zero, and false). Lodash checks only for null and undefined.
_.defaultTo(user.name, "Guest")defaultValue RequiredThe fallback when value is nullish. Can be any type—string, number, object, or even null if you intentionally want null as the default.
_.defaultTo(cfg.timeout, 5000)return value value | defaultNot a function—immediately resolves to one of the two inputs. Safe to embed in object literals and return statements.
return _.defaultTo(n, 0)not for "" ImportantTo treat empty string as missing, combine checks: value === "" ? fallback : _.defaultTo(value, fallback) or use || deliberately.
_.defaultTo("", "x") // ""For filling multiple missing object properties at once, see _.defaults() in the object category—not _.defaultTo().
Practical _.defaultTo() patterns with copy-ready code, sample output, and interactive Try It Yourself labs.
Replace null and undefined while keeping other values intact.
When a property is missing from parsed JSON, supply a display name.
console.log(_.defaultTo(undefined, "Guest")); // "Guest"
console.log(_.defaultTo(null, "Guest")); // "Guest"
console.log(_.defaultTo("Ada", "Guest")); // "Ada"Lodash uses a nullish test internally—same idea as value ?? "Guest". Defined strings pass through unchanged.
Unlike ||, _.defaultTo() preserves meaningful falsy values.
console.log(_.defaultTo(0, 10)); // 0
console.log(_.defaultTo("", "empty")); // ""
console.log(_.defaultTo(false, true)); // false
// || would replace all of the above with the fallback
console.log(0 || 10); // 10
console.log("" || "empty"); // "empty"Page size 0, an cleared text field "", and a feature flag false are valid states—defaultTo respects them.
Configuration, data cleanup, and URL/query parsing.
Merge user settings with defaults when optional keys are nullish.
const settings = {
timeout: 3000,
maxRetries: null,
theme: undefined
};
const apiTimeout = _.defaultTo(settings.timeout, 5000);
const retries = _.defaultTo(settings.maxRetries, 3);
const theme = _.defaultTo(settings.theme, "light");
console.log({ apiTimeout, retries, theme });
// { apiTimeout: 3000, retries: 3, theme: "light" }timeout: 3000 is kept. maxRetries: null and missing theme pick up defaults. For many keys at once, _.defaults() is an alternative.
Map API rows so null names and emails get readable placeholders—without touching valid empty strings if present.
const rows = [
{ id: 1, name: "Alice", email: "alice@example.com" },
{ id: 2, name: null, email: "bob@example.com" },
{ id: 3, name: "Charlie", email: undefined }
];
const sanitized = _.map(rows, (entry) => ({
id: entry.id,
name: _.defaultTo(entry.name, "Unknown"),
email: _.defaultTo(entry.email, "No email provided")
}));
console.log(sanitized[1].name); // "Unknown"
console.log(sanitized[2].email); // "No email provided"Only nullish database fields are replaced. If a user intentionally saved name: "", defaultTo would keep the empty string.
Parse an optional page index—0 must remain valid for the first page.
function parsePageParam(raw) {
if (raw === undefined || raw === null) {
return _.defaultTo(undefined, 1);
}
return Number(raw);
}
console.log(parsePageParam(undefined)); // 1 (default first page)
console.log(parsePageParam("0")); // 0 (valid index)
console.log(parsePageParam("3")); // 3Using raw || 1 would turn page 0 into page 1. defaultTo applies only when the param is absent, not when it parses to zero.
Compare operators and related Lodash helpers.
Choose the fallback tool that matches your intent.
const v = 0;
console.log(_.defaultTo(v, 99)); // 0
console.log(v ?? 99); // 0
console.log(v || 99); // 99
// Object-level: fill undefined keys on destination
const opts = { timeout: undefined, retries: 2 };
_.defaults(opts, { timeout: 5000, retries: 3, theme: "light" });
// opts -> { timeout: 5000, retries: 2, theme: "light" }Use _.defaultTo() for single-value nullish fallback in Lodash pipelines. Use ?? in modern JS without Lodash. Use _.defaults() when merging whole option objects.
_.defaultTo() WorksLodash takes the candidate value and the fallback to use if missing.
Tests whether value is null or undefined—and nothing else.
Return defaultValue when nullish; otherwise return value unchanged.
Falsy-but-valid values like 0 and "" survive the check.
null and undefined trigger the fallback—not empty strings or zero.value ?? defaultValue for the same inputs._.defaultTo() calls—one per value is clearer.|| knowingly._.defaultTo() is a small, precise helper: when data might be missing (null or undefined), supply a fallback without clobbering legitimate 0, false, or "" values.
Pair it with clear default constants, compare consciously with ||, and reach for _.defaults() when you are merging entire options objects.
_.defaultTo()Use these points when choosing fallback logic.
null / undefined only.
BasicsZero stays zero.
CriticalEmpty string OK.
PitfallSame as coalescing.
NativeFor object merge.
RelatedBefore ES2020’s ?? operator, _.defaultTo() was a popular way to avoid the || trap where 0 and "" were accidentally replaced. In new code you can use either—behavior matches for null and undefined.
Open the Try It editor, run the examples, and experiment with nullish fallback logic.
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