Do not use magic numbers when manipulating strings
Written byPhuoc Nguyen
Created
09 Mar, 2021
Category
Practice
Tags
JavaScript
It's quite often that we pass the index parameter when using string manipulation functions such as
`slice`, `splice`, `substr` or `substring`.Let's take a look at a simple example which converts a given date object to YYYY-MM-DD format.
Given a
`date` object, we can get the string representing the date in the ISO format:js
date.toISOString();
// '2021-03-09T01:42:46.002Z'The output is constructed by different parts which starts with the full date,
`2021-03-09` as we see in the example above.
So, it's easy to get the full date by extracting it from the ISO format:js
const format = (date) => date.toISOString().slice(0, 10);`10` is called a magic number, because when the other people look at the code, they don't have idea where the number comes from.Rather than using a magic number, it's recommended to explain what it is and how it's calculated:
js
// The better version
const FULL_DATE_LENGTH = 'YYYY-MM-DD'.length;
const format = (date) => date.toISOString().slice(0, FULL_DATE_LENGTH);#See also
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Phước Nguyễn