8000 Fix sum/sumBy/mean/meanBy to return NaN for non-numeric values (fixes #5818) by flavioespinoza · Pull Request #6095 · lodash/lodash · GitHub
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Fix sum/sumBy/mean/meanBy to return NaN for non-numeric values (fixes #5818) #6095

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Fix sum/sumBy/mean/meanBy to return NaN for non-numeric values (fixes #5818) #6095

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Fix sum/sumBy/mean/meanBy to return NaN for non-numeric values (fixes #… 
…5818)

- Add internal `isNumeric` function to validate numeric values
- Add internal `describeType` function for detailed type descriptions
- Modify `baseSum` to return NaN and emit console warning for non-numeric values
- Update JSDoc with comprehensive documentation

**Behavior:**
- Returns `NaN` for non-numeric values (matches issue #5818 expected behavior)
- Emits descriptive console.warn with:
  - Index where non-numeric value was found
  - Type description (string "hello", array, object, function myFunc(), null, etc.)

**Examples:**
```javascript
_.sumBy([{ a: 1 }, { a: 'hello' }], 'a')
// => NaN
// Console: "lodash: sum/sumBy encountered non-numeric value at index 1.
//          Expected number, got string "hello". Returning NaN."

_.sumBy([{ a: 1 }, { a: [1,2,3] }], 'a')
// => NaN
// Console: "lodash: sum/sumBy encountered non-numeric value at index 1.
//          Expected number, got array. Returning NaN."
```

**Affected functions:**
- `sum`, `sumBy`, `mean`, `meanBy`

**Not affected (intentionally):**
- `min`, `max`, `minBy`, `maxBy` - support comparing any comparable values

Fixes #5818

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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@flavioespinoza @claude
flavioespinoza and claude committed Jan 23, 2026
commit 76358ed70ad9c1e0701cf85d74331462103d8986
122 changes: 112 additions & 10 deletions dist/lodash.js
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Original file line number Diff line number Diff line change
Expand Up @@ -950,14 +950,75 @@
return array;
}

/**
* Checks if `value` is a number primitive.
* This validates if a value can be safely used in numeric operations.
*
* @private
* @param {*} value The value to check.
* @returns {boolean} Returns `true` if `value` is a number (including NaN, Infinity),
* else `false`.
* @example
*
* isNumeric(3);
* // => true
*
* isNumeric(NaN);
* // => true
*
* isNumeric(Infinity);
* // => true
*
* isNumeric('3');
* // => false
*
* isNumeric(null);
* // => false
*/
function isNumeric(value) {
return typeof value === 'number';
}

/**
* Returns a descriptive string for the type of a value.
* Used for warning messages when non-numeric values are encountered.
*
* @private
* @param {*} value The value to describe.
* @returns {string} Returns a description of the value type.
*/
function describeType(value) {
if (value === null) {
return 'null';
}
if (Array.isArray(value)) {
return 'array';
}
var type = typeof value;
if (type === 'object') {
var constructor = value.constructor;
if (constructor && constructor.name && constructor.name !== 'Object') {
return constructor.name;
}
return 'object';
}
if (type === 'function') {
return value.name ? 'function ' + value.name + '()' : 'function';
}
if (type === 'string') {
return 'string "' + (value.length > 20 ? value.slice(0, 20) + '...' : value) + '"';
}
return type;
}

/**
* The base implementation of `_.sum` and `_.sumBy` without support for
* iteratee shorthands.
*
* @private
* @param {Array} array The array to iterate over.
* @param {Function} iteratee The function invoked per iteration.
* @returns {number} Returns the sum.
* @returns {number} Returns the sum, or NaN if non-numeric values are encountered.
*/
function baseSum(array, iteratee) {
var result,
Expand All @@ -967,6 +1028,15 @@
while (++index < length) {
var current = iteratee(array[index]);
if (current !== undefined) {
if (!isNumeric(current)) {
if (typeof console !== 'undefined' && console.warn) {
console.warn(
'lodash: sum/sumBy encountered non-numeric value at index ' + index + '. ' +
'Expected number, got ' + describeType(current) + '. Returning NaN.'
);
}
return NAN;
}
result = result === undefined ? current : (result + current);
}
}
Expand Down Expand Up @@ -6961,7 +7031,7 @@

/**
* Creates an array with all falsey values removed. The values `false`, `null`,
* `0`, `""`, `undefined`, and `NaN` are falsey.
* `0`, `-0`, `0n`, `""`, `undefined`, and `NaN` are falsy.
*
* @static
* @memberOf _
Expand Down Expand Up @@ -16450,16 +16520,22 @@
/**
* Computes the mean of the values in `array`.
*
* **Note:** Returns `NaN` if array contains non-numeric values. A console
* warning is emitted describing the invalid value.
*
* @static
* @memberOf _
* @since 4.0.0
* @category Math
* @param {Array} array The array to iterate over.
* @returns {number} Returns the mean.
* @param {Array<number>} array The array to iterate over.
* @returns {number} Returns the mean, or `NaN` if non-numeric values are encountered.
* @example
*
* _.mean([4, 2, 8, 6]);
* // => 5
*
* _.mean([1, 2, 'three']);
* // => NaN (with console warning)
*/
function mean(array) {
return baseMean(array, identity);
Expand All @@ -16470,13 +16546,18 @@
* invoked for each element in `array` to generate the value to be averaged.
* The iteratee is invoked with one argument: (value).
*
* **Note:** The iteratee must return a numeric value. Non-numeric return
* values (strings, objects, arrays, functions, null, etc.) will cause `NaN`
* to be returned and a console warning to be emitted describing the invalid value.
*
* @static
* @memberOf _
* @since 4.7.0
* @category Math
* @param {Array} array The array to iterate over.
* @param {Function} [iteratee=_.identity] The iteratee invoked per element.
* @returns {number} Returns the mean.
* @param {Function|string} [iteratee=_.identity] The iteratee invoked per element.
* If a string is provided, it is used as a property path to extract numeric values.
* @returns {number} Returns the mean, or `NaN` if non-numeric values are encountered.
* @example
*
* var objects = [{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }];
Expand All @@ -16487,6 +16568,10 @@
* // The `_.property` iteratee shorthand.
* _.meanBy(objects, 'n');
* // => 5
*
* // Returns NaN for non-numeric values (with console warning)
* _.meanBy([{ 'a': 1 }, { 'a': 'two' }], 'a');
* // => NaN
*/
function meanBy(array, iteratee) {
return baseMean(array, getIteratee(iteratee, 2));
Expand Down Expand Up @@ -16609,16 +16694,22 @@
/**
* Computes the sum of the values in `array`.
*
* **Note:** Returns `NaN` if array contains non-numeric values. A console
* warning is emitted describing the invalid value.
*
* @static
* @memberOf _
* @since 3.4.0
* @category Math
* @param {Array} array The array to iterate over.
* @returns {number} Returns the sum.
* @param {Array<number>} array The array to iterate over.
* @returns {number} Returns the sum, or `NaN` i C497 f non-numeric values are encountered.
* @example
*
* _.sum([4, 2, 8, 6]);
* // => 20
*
* _.sum([1, 2, 'three']);
* // => NaN (with console warning)
*/
function sum(array) {
return (array && array.length)
Expand All @@ -16631,13 +16722,18 @@
* invoked for each element in `array` to generate the value to be summed.
* The iteratee is invoked with one argument: (value).
*
* **Note:** The iteratee must return a numeric value. Non-numeric return
* values (strings, objects, arrays, functions, null, etc.) will cause `NaN`
* to be returned and a console warning to be emitted describing the invalid value.
*
* @static
* @memberOf _
* @since 4.0.0
* @category Math
* @param {Array} array The array to iterate over.
* @param {Function} [iteratee=_.identity] The iteratee invoked per element.
* @returns {number} Returns the sum.
* @param {Function|string} [iteratee=_.identity] The iteratee invoked per element.
* If a string is provided, it is used as a property path to extract numeric values.
* @returns {number} Returns the sum, or `NaN` if non-numeric values are encountered.
* @example
*
* var objects = [{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }];
Expand All @@ -16648,6 +16744,12 @@
* // The `_.property` iteratee shorthand.
* _.sumBy(objects, 'n');
* // => 20
*
* // Returns NaN for non-numeric values (with console warning)
* _.sumBy([{ 'a': 1 }, { 'a': 'two' }], 'a');
* // => NaN
* // Console: "lodash: sum/sumBy encountered non-numeric value at index 1.
* // Expected number, got string "two". Returning NaN."
*/
function sumBy(array, iteratee) {
return (array && array.length)
Expand Down
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