Differences between the substr method and the substring method of JS string Truncation

The substr method returns a substring of the specified length starting from the specified position. The stringvar. substr (start [, length]) parameter is required. The String text or String object to extract the substring. Start is required. The starting position of the required substring. The index of the first character in the string is 0. Length is optional. The number of characters to be included in the returned substring. If the length is 0 or negative, an empty string is returned. If this parameter is not specified, the substring will continue to the end of stringvar. The following example demonstrates the substr method usage. Function SubstrDemo () {var s, ss; // declare the variable. Var s = "The rain in Spain falls mainly in the plain."; ss = s. substr (12, 5); // obtain The substring. Return (ss); // return "Spain ".} The substring method returns the substring at the specified position in the String object. StrVariable. substring (start, end) "String Literal". substring (start, end) parameter start indicates the starting position of the substring. The index starts from 0. End indicates the end position of the substring. The index starts from 0. The substring method returns a string that contains a substring from start to the end (excluding end. The substring method uses a small value in start and end as the starting point of the substring. For example, strvar. substring (0, 3) and strvar. substring (3, 0) return the same substring. If start or end is NaN or negative, replace it with 0. The length of the substring is equal to the absolute value of the difference between start and end. For example, the length of the substring returned in strvar. substring (0, 3) and strvar. substring (3, 0) is 3. The following example demonstrates the usage of the substring method. Function SubstringDemo () {var ss; // declare the variable. Var s = "The rain in Spain falls mainly in the plain .."; ss = s. substring (12, 17); // obtain The substring. Return (ss); // return the substring .}