All these methods are used to extract part of given string.

Declarations:

• slice(start, end); - slice from start (including) to end (excluding) and accepts negative values.
• substring(start, end); - same like slice but won't accepts negative values.
• substr(start, length); - same like slice but second param is length.

Below examples explain the differences.

const testString = "Hey, Welcome to urstrulyvishwaks articles";

// slice.
testString.slice(5,12); // start including end excluding.
> 'Welcome'

testString.slice(5); // only start value - Hence starting from 5 to end.
> 'Welcome to urstrulyvishwaks articles'

testString.slice(-25, -10); // accepts negative range.
> 'urstrulyvishwak'

// substring.
testString.substring(5,12);
> 'Welcome'

testString.substring(5);
> 'Welcome to urstrulyvishwaks articles'

testString.substring(-25, -10); // Didn't return any result as it won't support.
> ''

// substr.
testString.substr(5,7); // second param is length
>'Welcome'

testString.substr(5);
> 'Welcome to urstrulyvishwaks articles'

testString.substr(-25, 15);
> 'urstrulyvishwak'

Slice detailed article: here