String.prototype.slice()

indexStart

The index of the first character to include in the returned substring.

indexEnd Optional

The index of the first character to exclude from the returned substring.

A new string containing the extracted section of the string.

slice() extracts the text from one string and returns a new string.

slice() extracts up to but not including indexEnd. For example, str.slice(4, 8) extracts the fifth character through the eighth character (characters indexed 4, 5, 6, and 7):

              indexStart        indexEnd
                  ↓               ↓
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| T | h | e |   | m | i | r | r | o | r |

                  m   i   r   r
                 _______________
                      ↑
                    Result

• If indexStart >= str.length, an empty string is returned.
• If indexStart < 0, the index is counted from the end of the string. More formally, in this case, the substring starts at max(indexStart + str.length, 0).
• If indexStart is omitted, undefined, or cannot be converted to a number, it's treated as 0.
• If indexEnd is omitted or undefined, or if indexEnd >= str.length, slice() extracts to the end of the string.
• If indexEnd < 0, the index is counted from the end of the string. More formally, in this case, the substring ends at max(indexEnd + str.length, 0).
• If indexEnd <= indexStart after normalizing negative values (i.e. indexEnd represents a character that's before indexStart), an empty string is returned.

The following example uses slice() to create a new string.

const str1 = "The morning is upon us."; // The length of str1 is 23.
const str2 = str1.slice(1, 8);
const str3 = str1.slice(4, -2);
const str4 = str1.slice(12);
const str5 = str1.slice(30);
console.log(str2); // he morn
console.log(str3); // morning is upon u
console.log(str4); // is upon us.
console.log(str5); // ""

The following example uses slice() with negative indexes.

const str = "The morning is upon us.";
str.slice(-3); // 'us.'
str.slice(-3, -1); // 'us'
str.slice(0, -1); // 'The morning is upon us'
str.slice(4, -1); // 'morning is upon us'

This example counts backwards from the end of the string by 11 to find the start index and forwards from the start of the string by 16 to find the end index.

console.log(str.slice(-11, 16)); // "is u"

Here it counts forwards from the start by 11 to find the start index and backwards from the end by 7 to find the end index.

console.log(str.slice(11, -7)); // " is u"

These arguments count backwards from the end by 5 to find the start index and backwards from the end by 1 to find the end index.

console.log(str.slice(-5, -1)); // "n us"

• String.prototype.substr()
• String.prototype.substring()
• Array.prototype.slice()