Symbol.toPrimitive

The Symbol.toPrimitive is a symbol that specifies a function valued property that is called to convert an object to a corresponding primitive value.

Property attributes of Symbol.toPrimitive
Writable no
Enumerable no
Configurable no

Description

With the help of the Symbol.toPrimitive property (used as a function value), an object can be converted to a primitive value. The function is called with a string argument hint, which specifies the preferred type of the result primitive value. The hint argument can be one of "number", "string", and "default".

Examples

Following example describes how Symbol.toPrimitive property can modify the primitive value converted from an object.

// An object without Symbol.toPrimitive property.
var obj1 = {};
console.log(+obj1);     // NaN
console.log(`${obj1}`); // "[object Object]"
console.log(obj1 + ""); // "[object Object]"

// An object with Symbol.toPrimitive property.
var obj2 = {
  [Symbol.toPrimitive](hint) {
    if (hint == "number") {
      return 10;
    }
    if (hint == "string") {
      return "hello";
    }
    return true;
  }
};
console.log(+obj2);     // 10      -- hint is "number"
console.log(`${obj2}`); // "hello" -- hint is "string"
console.log(obj2 + ""); // "true"  -- hint is "default"

Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Symbol.toPrimitive' in that specification.
Standard Initial definition.
ECMAScript 2017 Draft (ECMA-262)
The definition of 'Symbol.toPrimitive' in that specification.
Draft  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 48 44 (44) ? ? ?
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support ? ? 44.0 (44) ? ? ?

See also

Document Tags and Contributors

 Contributors to this page: ZeikJT, The-Quill, fscholz, arai
 Last updated by: ZeikJT,