The substr() method extracts parts of a string, beginning at the character at the specified position, and returns the specified number of characters.
|start||Required. The position where to start the extraction. First character is at index 0.|
If start is positive and greater than, or equal, to the length of the string, substr() returns an empty string.
If start is negative, substr() uses it as a character index from the end of the string.
If start is negative or larger than the length of the string, start is set to 0|
|length|Optional . The number of characters to extract. If omitted, it extracts the rest of the string|
let str = "Hello world!"; let res = str.substr(1, 4);
The result of res will be: