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tessl/npm-lodash-concat

Creates a new array concatenating array with any additional arrays and/or values

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Lodash Concat

Lodash concat creates a new array concatenating an array with any additional arrays and/or values. This function provides a reliable way to combine arrays without mutating the original array, handling edge cases gracefully.

Package Information

  • Package Name: lodash
  • Package Type: npm
  • Language: JavaScript
  • Installation: npm install lodash (concat is part of the main lodash library)

Core Imports

import { concat } from "lodash";

For CommonJS:

const { concat } = require("lodash");

Alternative global usage:

// If lodash is loaded globally
_.concat(array, ...values);

Basic Usage

import { concat } from "lodash";

// Basic concatenation
const array = [1];
const result = concat(array, 2, [3], [[4]]);
console.log(result);
// => [1, 2, 3, [4]]

// Original array is unchanged
console.log(array);
// => [1]

// Handling null/undefined input
const nullResult = concat(null, 1, 2);
console.log(nullResult);
// => [1, 2]

const undefinedResult = concat(undefined, 1, [2], [[3]]);
console.log(undefinedResult);
// => [1, 2, [3]]

// Non-array first parameter
const stringResult = concat("hello", " ", "world");
console.log(stringResult);
// => ["hello", " ", "world"]

Capabilities

Array Concatenation

Creates a new array by combining the input array with additional values, handling non-array inputs gracefully.

/**
 * Creates a new array concatenating array with any additional arrays and/or values.
 * @param {Array} array - The array to concatenate  
 * @param {...*} [values] - The values to concatenate
 * @returns {Array} Returns the new concatenated array
 */
function concat(array, ...values);

Behavior Details:

  • Immutable Operation: Never modifies the original array
  • Type Conversion: If array is not an array:
    • null or undefined becomes an empty array []
    • Other values become a single-element array [Object(value)]
  • Flattening: Values are flattened by one level only
  • Variable Arguments: Accepts any number of additional values after the first parameter
  • Sparse Arrays: Treats sparse arrays as dense arrays (undefined values are preserved)

Usage Examples:

import { concat } from "lodash";

// Multiple arrays and values
const arr1 = [1, 2];
const arr2 = [3, 4];
const result = concat(arr1, arr2, 5, [6, 7]);
console.log(result);
// => [1, 2, 3, 4, 5, 6, 7]

// Nested array handling (one level flattening)
const nested = concat([1], [[2, 3]], [[[4]]]);
console.log(nested);
// => [1, [2, 3], [[4]]]

// Empty array concatenation
const empty = concat([], 1, 2, 3);
console.log(empty);
// => [1, 2, 3]

// Mixed data types
const mixed = concat([1, 2], "hello", true, { key: "value" });
console.log(mixed);
// => [1, 2, "hello", true, { key: "value" }]

// Sparse arrays (treated as dense)
const sparse = concat(Array(2), Array(1));
console.log(sparse);
// => [undefined, undefined, undefined]
console.log('0' in sparse); // => true
Workspace
tessl
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npmpkg:npm/lodash@4.5.x#concat
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