substr and slice methods of strings in JavaScript

July 12th, 2020 | 2 mins read

#string

substr and slice are string methods in JavaScript to cut out substrings from the full string. There's also substring but it's similar to slice. This answer on StackOverFlow explains the difference between substring and slice.

Let's look at substr and slice in detail.

slice

Note that this is different from the slice method in arrays but works similarly.

Syntax for slice

string.slice(from, to);

from is the point (index position) which the cutting starts from in the string and to is the point where the cutting stops. But, unlike the from which the character at that point is included in the returned string, the character at to is not included.

Example for slice

const str = 'Hello World';
const subString = str.slice(0, 3);
console.log(subString);
// Hel

The first argument (from) here is 0, which is, of course, the beginning of the string. At the beginning is 'H'.

The last argument (to) is 5, which is the index of the character, 'l'. As explained in the syntax, the returned value is H to the second l but without l - 'Hel'

substr

Syntax for substr

string.substr(from, length-to-cut);

Similar to slice, from is the starting index position to begin cutting but unlike slice, substr's second argument is the length of characters to cut (not the index position to stop).

Example for substr

const str = 'Hello World';
const subString = str.substr(1, 3);
console.log(subString);
// ell

The first argument (from) here is 1, which is the index position for the character 'e'.

The second argument (length-to-cut) is 3, which means starting from 'e', cut out 3 characters.

If slice was used instead, the result would be 'el' - 1 being the starting point ('e') and 3 being the ending point ('o') which is not included in the returned value.

Wrap up

slice (just like substring) works like (from, to) while substr works like (from, length-to-cut)

These methods can be used to achieve the same thing, but, they have their key differences. I believe with this article, you not only know the uniqueness of these two methods but also how to apply them.

Thanks for reading : )

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Dillion Megida

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