What's the difference between substr() and substring()?

There are two JavaScript functions to extract a parts of a string: substr and substring.

Both functions extracts a substring starting from an index.

The difference between substr and substring is that substr extracts the substring based on its length, whereas substring extracts the substring based on its start and end indexes.

Example:

const test = 'Lorem ipsum dolor sit amet';
console.log('substr:', test.substr(6, 10));
console.log('substring:', test.substring(6, 10));

Outputs:

substr:ipsum dolo
substring:ipsu

The following images highlights the differences between the two functions:

Note that since substr is a deprecated feature, you should avoid using it and favour substring instead.