From MDN.

Method Purpose
String() Creates a new String object. It performs type conversion when called as a function, rather than as a
constructor, which is usually more useful.
.length Reflects the length of the string. Read-only.
.at() Returns the character (exactly one UTF-16 code unit) at the specified index. Accepts negative integers, which
count back from the last string character.
.charAt() Returns the character (exactly one UTF-16 code unit) at the specified index.
.charCodeAt() Returns a number that is the UTF-16 code unit value at the given index.
.codePointAt() Returns a nonnegative integer Number that is the code point value of the UTF-16 encoded code point starting at
the specified pos.
.concat() Combines the text of two (or more) strings and returns a new
.includes() Determines whether the calling string contains search
.endsWith() Determines whether a string ends with the characters of the string search
.indexOf() Returns the index within the calling String object of the first occurrence of searchValue, or -1 if not found.
.lastIndexOf() Returns the index within the calling String object of the last occurrence of searchValue, or -1 if not found.
.localeCompare() Returns a number indicating whether the reference string compareString comes before, after, or is equivalent to
the given string in sort order.
.match() Used to match regular expression regexp against a
.matchAll() Returns an iterator of all regexp’s matches.
.normalize() Returns the Unicode Normalization Form of the calling string value.
.padEnd() Pads the current string from the end with a given string and returns a new string of the length targetLength.
.padStart() Pads the current string from the start with a given string and returns a new string of the length targetLength.
.repeat() Returns a string consisting of the elements of the object repeated count times.
.replace() Used to replace occurrences of searchFor using replaceWith. searchFor may be a string or Regular Expression, and
replaceWith may be a string or function.
.replaceAll() Used to replace all occurrences of searchFor using replaceWith. searchFor may be a string or Regular Expression,
and replaceWith may be a string or function.
.search() Search for a match between a regular expression regexp and the calling
.slice() Extracts a section of a string and returns a new
.split() Returns an array of strings populated by splitting the calling string at occurrences of the substring sep.
.startsWith() Determines whether the calling string begins with the characters of string search
.substring() Returns a new string containing characters of the calling string from (or between) the specified index (or
indices).
.toLocaleLowerCase() The characters within a string are converted to lowercase while respecting the current locale.
For most languages, this will return the same as toLowerCase()		 .
.toLocaleUpperCase( [locale, …locales]) The characters within a string are converted to uppercase while respecting the current locale.
For most languages, this will return the same as toUpperCase()
.toLowerCase() Returns the calling string value converted to lowercase.
.toString() Returns a string representing the specified object. Overrides the Object.prototype.toString()
.toUpperCase() Returns the calling string value converted to uppercase.
.trim() Trims whitespace from the beginning and end of the
.trimStart() Trims whitespace from the beginning of the
.trimEnd() Trims whitespace from the end of the
.valueOf() Returns the primitive value of the specified object. Overrides the Object.prototype.valueOf()