JavaScript Interview and Prep: Currying

Marika Lam

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Jun 20, 2024

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What is Currying

• Currying is a technique in functional programming that allows you to transform a function that takes multiple arguments into a sequence of functions that each take one argument.
• Here is a simple JavaScript method (no curry)

function add (a, b) {
    return a + b;
}

add(3, 4); // returns 7

• Now let’s curry this function

function add (a) {
    return function (b) {
        return a + b;
    }
}

• This is a function that takes one argument, a, and returns a function that takes another argument, b, and that function returns their sum.

add(3)(4); // returns 7

var add3 = add(3); // returns a function

add3(4); // returns 7

• The first statement returns 7, like the add(3, 4) statement.
• The second statement defines a new function called add3 that will add 3 to its argument. This is what some may call a closure.
• The third statement uses the add3 operation to add 3 to 4, again producing 7 as a result.

Example prompt

• Please implement a curry() function, which accepts a function and return a curried one.

Solution