Currying in JavaScript transforms a function with multiple arguments into a nested series of functions, each taking a single argument. The parent function takes the first provided argument and returns the function that takes the next argument and this keeps on repeating till the number of arguments ends. The function that receives the last argument returns the expected result.

What is currying?

Difficulty: 5/10

partial application, function composition, higher-order functions

Currying is a functional programming technique where a function that takes multiple arguments is transformed into a sequence of functions, each taking a single argument.

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Currying in JavaScript transforms a function with multiple arguments into a nested series of functions, each taking a single argument.
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The parent function takes the first provided argument and returns the function that takes the next argument and this keeps on repeating till the number of arguments ends. The function that receives the last argument returns the expected result.

Scenario Questions

0-2 years experience

1We have a simple function add(a, b) that returns a + b. How would you rewrite it using currying so that you can call add(2)(3)?
2If you have a curried function multiply(a)(b) and you call multiply(5) without the second argument, what does it return and why?

2-5 years experience

1Our team is building a form validation library where each validator is a curried function that takes a config object first, then the value to validate. A bug appears where the config is shared across calls. What could be causing this and how would you fix it?

Follow-up Questions

Can you compare currying to partial application and tell me when you'd choose one over the other?
How does JavaScript's handling of this and closures affect a curried function's behavior?
What impact does currying have on stack traces and debugging in production?