Substring. A string has 10 characters, but we wantonly 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.
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);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.
Detail For substring with 1 argument, the remaining part of the string (after the index specified) is included.
var value = "x_frog";
// Skip over first 2 characters.
var result = value.substring(2);
console.log("VALUE: " + value);
console.log("SUBSTRING: " + result);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.
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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Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.