JavaScript String Substring | Extract Substring from String

JavaScript String Substring | Extract Substring from String

In this tutorial, you will learn all about JavaScript string.substring() method and how to extract a substring from a string using this method.

JavaScript string.substring() method

The JavaScript string.substring() method returns the new sub string from a given string, the basis of the provided index.

The following syntax demonstrates substring() method:

str.substring(indexA [, indexB])

The string.substring() method takes 2 parameters: indexA and indexB:

  • The indexA is a position where to start the extraction.
  • The indexB  is a position where to end the extraction.

Remember some important things about substring() method:

  • If you ignore the indexB, the substring() returns the substring to the end of the string.
  • If indexA equals indexB, the substring() method returns an empty string.
  • If indexAis greater than the indexB, the substring() swaps their roles: the indexA becomes the indexB.
  • If either indexA or indexB is less than zero or greater than the string.length, the substring() considers it as zero (0).
  • If any parameter is NaN, the substring() treats it as if it were zero (0).

Examples: JavaScript substring() method

Let’s take look at some examples of string.substring() js string method.

1) Extracting a substring from the starting of the string

Extract a substring from the between two indexes of provided string, and return a new substring.

See the following example:

let string = 'Hello, Programmer';
let substring = string.substring(0,4);

console.log(substring);

Output:

Hello

2) Extracting a substring to the end of the string

The following example uses the javascript string.substring() to extract at position 6, and return a new sub string.

See the following example:

let string = 'Hello, Programmer';
let substring = string.substring(6);

console.log(substring);

Output:

Programmer

Conclusion

In this tutorial, you have learned all about JavaScript string.substring() method.

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