javaScript useful method

Javascript string and array function

toLowerCase: toLowerCase() method is convert any string to lower case.
toUpperCase: toUpperCase() method is convert any sting to upper case
Searching method:
indexOf:
includes:
startWith:
endWith:
Array methods
split:
slice:
subStr:
subString:
concat:
join:

Array searching method
isArray:
indexOf:
includes:
concat: