Create a function that accepts a single parameter
Written byPhuoc Nguyen
Created
15 Mar, 2021
Last updated
08 Sep, 2022
Category
Tip
Tags
JavaScript
Contributors
Quite often, we use the
`map` function to transform each item of an array into a new one. However, it's common to see an issue if we don't pass the parameter to the mapper function.For example, the following code converts each item of array into a number:
js
['1', '2', '3', '4', '5'].map((v) => parseInt(v));
// [1, 2, 3, 4, 5]However, the result isn't correct if we shorten it as below:
js
['1', '2', '3', '4', '5'].map(parseInt);
// [1, NaN, NaN, NaN, NaN]The issue is caused by the fact that the mapper function accepts three parameters which are the array item, index, and the array.
Calling
`.map(parseInt)` means that we pass the item index to `parseInt` as the second parameter. As a result, we will see `NaN`.This leads to a requirement of building a function that accepts only the first parameter, and ignore the remaining parameters.
js
const unary = (fn) => (params) => fn(params);The
`unary` function creates a wrapper of a function, and ignores all parameters except the first one. With that function in our hand, we can pass the mapper to the `map` function like this:js
['1', '2', '3', '4', '5'].map(unary(parseInt));
// [1, 2, 3, 4, 5]#See also
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Phước Nguyễn