Lodash _.sum() Method

Beginner
5 min read
Updated: Nov 2026
5 examples
Math
Decorative image with the word SUM

Definition

Computes the sum of the values in array. Part of Lodash Math (stable — not deprecated). Empty, null, and undefined arrays return 0 (unlike _.mean([]), which is NaN).

Pass the numbers or collection shown below. Check the return value before you chain another math helper.

Syntax

Call _.sum. Start with this line.

Lodash
_.sum(array)
CallWhat it does
_.sum(array)Primary signature.

Prefer import sum from "lodash/sum" when you want a smaller bundle.

Library declarations
Lodash
_.sum(array)

Parameters

ParameterDescription
arrayRequired. Array to iterate over

Return Value

Return ValueDescription
*The sum (number), or 0 if empty/nullish

Lodash Examples

Example 1 — Official: Sum an Array

Add every number in the list.

Lodash
console.log(_.sum([4, 2, 8, 6])); // 20
Try It Yourself

How It Works

  1. Input. Flat number array [4, 2, 8, 6].
  2. Add. Lodash folds with native +.
  3. Result. 20 — matches the official docs.
  4. Tip. Prefer this over a hand-rolled loop for clarity.

Example 2 — Empty and Nullish → 0

Missing data does not throw — you get a safe zero.

Lodash
console.log(_.sum([]));   // 0
console.log(_.sum(null)); // 0
console.log(_.sum());     // 0
Try It Yourself

How It Works

  1. Empty array. No values to add → 0.
  2. null / missing. Same short-circuit → 0.
  3. Contrast. _.mean([]) is NaN — different guard.
  4. Use. Safe default when totals may be missing.

Example 3 — Negatives and Decimals

Signed numbers work; floats keep native precision.

Lodash
console.log(_.sum([-2, 5, 1])); // 4
console.log(_.sum([1.5, 2.5])); // 4
console.log(_.sum([0.1, 0.2])); // 0.30000000000000004
Try It Yourself

How It Works

  1. Negatives. -2 + 5 + 1 → 4.
  2. Decimals. 1.5 + 2.5 → 4.
  3. Float trap. 0.1 + 0.2 is not exact in IEEE-754.
  4. Money tip. Sum integer cents, then divide.

Example 4 — String Concatenation Trap

One string can turn the whole sum into text.

Lodash
console.log(_.sum([1, "2", 3]));           // "123"
console.log(_.sum([1, "2", 3].map(Number))); // 6
Try It Yourself

How It Works

  1. Seed. Starts at 1.
  2. String hit. 1 + "2" → "12".
  3. Continue. "12" + 3 → "123".
  4. Fix. Map with Number before summing.

Example 5 — _.sum vs _.sumBy

Use sumBy when values live on objects.

Lodash
var nums = [4, 2, 8, 6];
var rows = [{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }];

console.log(_.sum(nums));        // 20
console.log(_.sumBy(rows, "n")); // 20
Try It Yourself

How It Works

  1. Flat list. _.sum adds numbers directly.
  2. Objects. _.sumBy(rows, "n") pulls each n.
  3. Same total. Both paths yield 20.
  4. Rule. Numbers → sum; properties → sumBy.
Compatibility

Browser & Runtime Support

_.sum is a Lodash Math helper available in 4.x (and earlier builds). It runs anywhere Lodash runs — modern browsers (via CDN or bundle) and Node.js / Bun / Deno with npm install lodash. Native equivalents use array.reduce((a, b) => a + b, 0); Lodash additionally returns 0 for empty/nullish input.

✓ Stable · Lodash 4.x

_.sum()

Available in [email protected] full builds and the lodash/sum modular import. Works in evergreen browsers and current Node LTS when Lodash is installed.

100% With Lodash 4.x
Google Chrome Supported · Desktop & Mobile
Full support
Mozilla Firefox Supported · Desktop & Mobile
Full support
Apple Safari Supported · macOS & iOS
Full support
Microsoft Edge Supported · Chromium
Full support
Internet Explorer No native support · Use a polyfill
Polyfill
Opera Supported · Modern versions
Full support
Samsung Internet Supported · Android
Full support
Bun Supported · JavaScript runtime
Supported
Deno Supported · JavaScript runtime
Supported
Node.js Supported · Server runtime
Supported
Android WebView Supported · Modern WebView
Full support
_.sum Lodash 4.x

Bottom line: Safe for production once Lodash is on the page or in your bundle. Prefer import sum from "lodash/sum" for smaller builds. Keep the list numeric — strings concatenate.

Frequently Asked Questions

_.sum(array) computes the sum of the values in array. Official docs: _.sum([4, 2, 8, 6]) → 20. Empty, null, and undefined arrays return 0.
_.sum short-circuits empty/nullish input to 0. _.mean divides sum by length, so empty becomes 0 / 0 → NaN.
Lodash uses native +. After the first number, hitting a string switches to string concatenation: 1 + '2' → '12', then '12' + 3 → '123'. Coerce with _.sum(arr.map(Number)) when needed.
No. _.sum([0.1, 0.2]) can still show 0.30000000000000004 — same as native +. For money, work in integer cents or use a decimal library.
Use _.sumBy when items are objects and you need to sum a property or iteratee result — for example _.sumBy(users, 'age'). _.sum expects a flat list of numbers.
Use import sum from "lodash/sum" or require("lodash/sum") so bundlers can tree-shake. Full build: import _ from "lodash" then _.sum.

Next: _.sumBy()

Sum values from objects using a property or iteratee.

_.sumBy() tutorial →

About the author

Mari Selvan M P
Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

  • Experience 12 years building web and cloud systems
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I write practical tutorials so students and working developers can learn by doing—from databases and APIs to deployment on AWS.

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