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Zip Arrays

Q: Zip Arrays

**Target Audience:** Engineers preparing for practical JavaScript coding interviews. **Difficulty:** Easy > **How to read this doc:** a real, easy-to-misjudge detail this question tests — what genuinely appears in a tuple slot when one input array is SHORTER than the others — was verified with a direct `=== undefined` check (not just `JSON.stringify`, which would misleadingly display it as the string `"null"`): the missing slot is genuinely `undefined`, matching real, standard JavaScript array-hole/out-of-bounds-access behavior. ## 1. The problem, restated Combine `N` input arrays into a single array of length equal to the LONGEST input array, where the `i`-th output tuple contains the `i`-th element from EVERY input array (in the same order the arrays were passed) — with a shorter array correctly contributing `undefined` for any index beyond its own real length, matching lodash's own well-known `_.zip` contract. ## 2. Clarifying questions a strong candidate asks | Question | Why

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6 of 154

The problem

Problem, as an interviewer would state it: "Implement zip(...arrays) — combining multiple arrays into a single array of grouped tuples, where the Nth tuple contains the Nth element from every input array, matching lodash's own well-known _.zip behavior."

Examples:

Code

zip([1,2,3], ["a","b","c"]); // [[1,"a"], [2,"b"], [3,"c"]]

Clarifying questions expected:

What should the real, correct output length be if the input arrays have DIFFERENT lengths?
For a shorter array, what value should genuinely appear in the tuple slot beyond its own length?
Does this need to support any number of input arrays, or just exactly two?

Code / implementation expected: Yes — real, direct proof zipping equal-length arrays, zipping unequal-length arrays (confirming the missing slot is genuinely undefined), and confirming any number of input arrays is supported.

array

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Solution

Target Audience: Engineers preparing for practical JavaScript coding interviews. Difficulty: Easy

How to read this doc: a real, easy-to-misjudge detail this question tests — what genuinely appears in a tuple slot when one input array is SHORTER than the others — was verified with a direct === undefined check (not just JSON.stringify, which would misleadingly display it as the string "null"): the missing slot is genuinely undefined, matching real, standard JavaScript array-hole/out-of-bounds-access behavior.

1. The problem, restated

Combine N input arrays into a single array of length equal to the LONGEST input array, where the i-th output tuple contains the i-th element from EVERY input array (in the same order the arrays were passed) — with a shorter array correctly contributing undefined for any index beyond its own real length, matching lodash's own

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6 min read · 9 sections

Run the code

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JavaScriptReal, direct proof: zip() correctly combines equal and unequal-length arrays, with a direct check confirming a missing slot is genuinely undefined

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