substr() method extracts parts of a string, beginning at the character at the specified index, and returns the specified number of characters. It does not change the original string.
substr() method accepts two parameters one is start and other is length
str.substr(start , length)
a) Start: start defines the starting index from where the sub string is to be extracted from the base string.
b) length: length defines the number of characters to be extracted starting from the start in the given string. If the second argument to the function is undefined then all the characters from the start till the end of the length is extracted.
In the following example, the arguments given are (7, 17). So, substr() method obtain sub string starting from index 7 to a length of 17 characters, there by giving "Spacex, Neuralink" as output.
<html> <body> <p id="substring"></p> <script> var str = "Tesla, Spacex, Neuralink, Solarcity"; var res = str.substr(7,17); document.getElementById("substring").innerHTML = res; </script> </body> </html>