String .slice() / substring()

// Extracts from the start position to the end of the string.
string.slice(startIndex)
string.slice(startIndex, endIndex)

// Extracts a substring within the specified range.
string.substring(startIndex)
string.substring(startIndex, endIndex)

var str = "JavaScript";

// Extract using slice.
console.log(str.slice(4));     // Outputs "Script".
console.log(str.slice(0, 4));  // Outputs "Java".
console.log(str.slice(-6));    // Extracts 6 characters from the end, outputs "Script".
console.log(str.slice(-6, -3)); // Outputs "Scr".

// Extract using substring.
console.log(str.substring(4));     // Outputs "Script".
console.log(str.substring(0, 4));  // Outputs "Java".

// Difference between slice and substring.
console.log(str.slice(4, 0));      // Returns an empty string "".
console.log(str.substring(4, 0));  // Arguments are swapped, outputs "Java".

string.slice() and string.substring() are both methods for extracting a portion of a string. Both return characters from the start index up to, but not including, the end index, and neither modifies the original string.

The key difference between the two methods lies in how they handle negative values and argument order. string.slice() treats negative values as offsets from the end of the string, making it well-suited for extracting characters from the end. string.substring(), on the other hand, converts negative values to 0 and automatically swaps the arguments if the start index is greater than the end index.

In general, string.slice() behaves more intuitively and is recommended in most situations. Arrays also have a method of the same name, array.slice(), which works in nearly the same way.