String() constructor

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The String() constructor creates String objects. When called as a function, it returns primitive values of type String.

Syntax

js
new String(thing)
String(thing)

Note: String() can be called with or without new, but with different effects. See Return value.

Parameters

thing

Anything to be converted to a string.

Return value

When String() is called as a function (without new), it returns value coerced to a string primitive. Specially, Symbol values are converted to "Symbol(description)", where description is the description of the Symbol, instead of throwing.

When String() is called as a constructor (with new), it coerces value to a string primitive (without special symbol handling) and returns a wrapping String object, which is not a primitive.

Warning: You should rarely find yourself using String as a constructor.

Examples

String constructor and String function

String function and String constructor produce different results:

js
const a = new String("Hello world"); // a === "Hello world" is false
const b = String("Hello world"); // b === "Hello world" is true
a instanceof String; // is true
b instanceof String; // is false
typeof a; // "object"
typeof b; // "string"

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

Using String() to stringify a symbol

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

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

Specifications

Specification
ECMAScript Language Specification
# sec-string-constructor

Browser compatibility

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See also