thing

Anything to be converted to a string.

WhenString() is called as a function (withoutnew), it returnsvaluecoerced to a string primitive. Specially,Symbol values are converted to"Symbol(description)", wheredescription is thedescription of the Symbol, instead of throwing.

WhenString() is called as a constructor (withnew), it coercesvalue to a string primitive (without special symbol handling) and returns a wrappingString object, which isnot a primitive.

String function and String constructor produce different results:

const a = new String("Hello world"); // a === "Hello world" is falseconst b = String("Hello world"); // b === "Hello world" is truea instanceof String; // is trueb instanceof String; // is falsetypeof a; // "object"typeof b; // "string"

Here, the function produces a string (theprimitive type) as promised.However, the constructor produces an instance of the type String (an object wrapper) andthat's why you rarely want to use the String constructor at all.

String() is the only case where a symbol can be converted to a string without throwing, because it's very explicit.

const sym = Symbol("example");`${sym}`; // TypeError: Cannot convert a Symbol value to a string"" + sym; // TypeError: Cannot convert a Symbol value to a string"".concat(sym); // TypeError: Cannot convert a Symbol value to a string

const sym = Symbol("example");String(sym); // "Symbol(example)"

• Numbers and strings guide