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• Symbol
  • Symbols and privacy
  • Adding a description to symbols
  • Symbol.toPrimitive
  • Symbol.toStringTag
  • Symbol.isConcatSpreadable

Symbol

• symbol is a primitive value that can be created using a function named Symbol.
• What makes this primitive value interesting is that it is guaranteed to be unique.
• Now, symbols can be object keys as well
• Symbols allow JavaScript to add new properties to objects that cannot conflict with the existing properties on objects that others might have used in their code
• Symbols help keep the promise of backward compatibility
• Symbol values can be created using the Symbol function.
• It’s important to note that the Symbol function must be invoked without the new keyword.

const sym = Symbol();

const obj = {};
obj[sym] = "hello";

console.log(obj[sym]); // hello

const sym = Symbol();

const obj = {
  [sym]: "hello"
};

console.log(obj[sym]); // hello

Symbols and privacy

• symbol keys are not private

const name = Symbol();

const person = {
  [name]: "John Doe"
};

console.log(person.name); // undefined
console.log(person["name"]); // undefined
console.log(person[name]); // John Doe

const name = Symbol();

const person = {
  [name]: "John Doe",
  age: 20
};

console.log(Object.getOwnPropertyDescriptors(person));
/*
{
  age: { value: 20, writable: true, enumerable: true, configurable: true },
  [Symbol()]: {
    value: 'John Doe',
    writable: true,
    enumerable: true,
    configurable: true
  }
}
*/


console.log(Object.getOwnPropertySymbols(person));
// [ Symbol() ]

Adding a description to symbols

Symbol.toPrimitive

Symbol.toStringTag

Symbol.isConcatSpreadable