EasyDSAAsked in 20246 min read

Partial application bindings

Q: Partial application bindings

**Target Audience:** Engineers preparing for practical JavaScript coding interviews. **Difficulty:** Easy > **How to read this doc:** the real, key correctness claim this question tests — that the ORIGINAL function remains genuinely unaffected and independently reusable after `partial()` is called on it — was verified directly: calling the unmodified original `add3(1, 2, 3)` after creating `addTo5` still returned the correct, real, un-partial-applied result. ## 1. The problem, restated Pre-fill one or more LEADING arguments of a function, returning a genuinely NEW function that, when eventually called, concatenates the preset arguments with whatever new arguments that later call provides, and invokes the original — a real, general-purpose technique for creating specialized versions of a more general function, without needing a specific `this` binding (the real, distinguishing difference from `bind`). ## 2. Clarifying questions a strong candidate asks | Question | Why it matters |

906 views

25 of 154

The problem

Problem, as an interviewer would state it: "Implement partial(fn, ...presetArgs) — returning a genuinely NEW function that, when LATER called, invokes fn with the preset arguments prepended to whatever new arguments the later call provides."

Examples:

Code

function add3(a, b, c) { return a + b + c; }
const addTo5 = partial(add3, 5);
addTo5(2, 3); // 10

Clarifying questions expected:

Does this need to support pre-filling MORE than one leading argument, not just the first?
Should the ORIGINAL function remain genuinely unaffected/reusable after calling partial() on it?
How does this genuinely differ from bind() — is partial application a distinct, real concept, or just a simplified bind?

Code / implementation expected: Yes — real, direct proof pre-filling both a single and multiple leading arguments, confirming the original function is genuinely unaffected and reusable afterward.

js-coding
utility
algorithm

Try it yourself

Sketch your approach before you read the solution. That is what the interview tests.

Stuck? Get a hint.

A short nudge toward the approach. It will not give the answer away.

Solution

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

How to read this doc: the real, key correctness claim this question tests — that the ORIGINAL function remains genuinely unaffected and independently reusable after partial() is called on it — was verified directly: calling the unmodified original add3(1, 2, 3) after creating addTo5 still returned the correct, real, un-partial-applied result.

1. The problem, restated

Pre-fill one or more LEADING arguments of a function, returning a genuinely NEW function that, when eventually called, concatenates the preset arguments with whatever new arguments that later call provides, and invokes the original — a real, general-purpose technique for creating specialized versions of a more general function, without needing a specific this binding (the real, distinguishing differen

The solution is hidden so you can try first

6 min read · 9 sections

Run the code

Edit the code and run it here. Each console line with an expected value becomes a test.

JavaScriptReal, direct proof: partial() correctly pre-fills leading arguments, leaving the original function genuinely unaffected and independently reusable afterward

Practice

Discussion

Other approaches, follow-ups and how it went in real interviews.

No comments yet. Share how you would answer it.

Question 25 of 154 in JavaScript coding

Keep your momentum going.

Mark this question solved to track your progress, then take the next one while it is fresh.

All JavaScript coding questions

Up nextEasy→

Implement Promise.race()

Continue