var str = " Hello World ";
str.toUpperCase (); // convert a string to upper case
str.toLowerCase (); // string to lowercase
str.indexOf ( "World"); // index string exists if the first letter of the index position of the index returns -1 otherwise if the string is "" Returns 0
str.concat ( "Tonight Night", "Mami"); // in the method of the string sequentially added to the string
str.slice (2,4); // taken preamble index starts at the post but does not contain an index
str.slice (-4, -2); // if the index is negative reverse order
str.substring (5,2); // will automatically distinguish between the start and end positions according to the index value of the size
str.substring (-4, -2); // index when the value is negative, then all converted to 0
str.substr (2,3); // before the start parameter refers to the index of the index value, the length of the index parameter is
str.split ( "", 1); // before division based on the reference characters, and then dividing the value stored in the array returned completely to determine the length of the array in accordance with the parameters
str.trim (); // remove both spaces string