The following string methods do not mutate the existing string.

str.endsWith(searchString) – returns (boolean), determines if a string ends with a searchString.

str.startsWith(searchString) – returns (boolean), determines if a string starts with a searchString.

str.includes(searchString) – returns (boolean), returns true if string includes searchString anywhere within it.

str.indexOf(searchString) – returns the first occurrence of the searchString or -1 if none found.

str.lastIndexOf – returns the last occurrence of the searchString or -1 if none found.

str.match(regexp) – returns the array of the first match of a regular expression.

str.search(regexp) – returns the index of the first match or -1 if not found.

str.replace(regexp|substr, newSubstr|function) – replaces occurrences that match either a string or a regular expression with a new string. Can also be passed a function that creates the new replacement string.

str.slice(beginIndex[, endIndex]) – returns a new string from beginIndex to endIndex.

str.split([separator[, limit]]) – returns an array or strings.

str.substr(start[, length]) – returns new string from the start index and of specified length or to the end if none provided.

trim() – returns a new string with whitespace (space, tab, no-break space, etc.) removed from both ends.

str.toUpperCase() – returns a new string with uppercases - might not work with all unicode chars.

str.toLowerCase() – returns a new string with lowercases - might not work with all unicode chars.

fromCharCode – returns a new string consisting of the characters represented from the Unicode.

normalize([form]) – returns new string of the normalized type.