JavaScript Substring Examples

Get a new string in a range from a start to end index from an existing string with the substring method.

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Substring. A string has 10 characters, but we want only a part of this string—the first 5, the last 3. With substring we get a string from within an existing string.

In JavaScript, substring receives 2 arguments: the first index of the substring we are trying to take, and the last index. The second argument is not a count.

First example. Let us begin with this example. We have an input string "cat123." To get the "cat" part, we use a first index of 0, and a last index of 3.
Argument 1: The index of the first char we are taking a substring at—the first char in a string is at index 0.
Argument 2: The last index of the substring. This is not a count, but rather another position in the string.
JavaScript program that uses substring var value = "cat123"; console.log("VALUE: " + value); // Take a substring of the first 3 characters. // ... Start at index 0. // ... Continue until index 3. var result = value.substring(0, 3); console.log("SUBSTRING: " + result); Output VALUE: cat123 SUBSTRING: cat

Substring, 1 argument. Substring can be used with just 1 argument. This is the start index. We can think of this argument as the number of characters we want to skip over.
Length: For substring with 1 argument, the remaining part of the string (after the index specified) is included.
JavaScript program that uses substring, 1 argument var value = "x_frog"; // Skip over first 2 characters. var result = value.substring(2); console.log("VALUE: " + value); console.log("SUBSTRING: " + result); Output VALUE: x_frog SUBSTRING: frog

CharAt, char indexes. For accessing an individual character in a string, consider charAt or directly accessing a character. For performance, directly using a character is a good solution.charAt

With substring, we have a way to extract parts of strings. For optimal performance, using the original string and not changing it at all is best, but this is not always possible.


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