how to cut an string to get only first 100 chars in js code example

Example 1: javascript get first 10 characters of string

var str = "Hello world That is reallly neat!";
var res = str.substring(0, 5);//get first 5 chars

Example 2: javascript only allow show first few characters from a string

var string = 'Hey, I am good';
string.substring(0,3); // show first 3 characters
//result "Hey"