The document discusses the Symbol data type in JavaScript, which provides unique identifiers for object properties. Symbol values can be used as identifiers for object properties, and Symbols are not enumerable, so property names using Symbols will not show up in for-in loops or Object.keys(). The document shows examples of creating Symbols and using them to set unique, non-enumerable properties on objects. It also discusses using Symbols with the toStringTag method to customize object string representations.

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2. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
var firstName = Symbol();
var person = {};
person[firstName] = "Eyal";
console.log( person[firstName] ); // "Eyal"

3. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
var firstName = Symbol("first name");
var person = {};
person[firstName] = "Eyal";
console.log("first name" in person); // false
console.log(person[firstName]); // "Eyal"
console.log(firstName); // "Symbol(first name)"
The Symbol function accepts an optional argument
that is the description of the symbol.

4. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
var symbol = Symbol("test symbol");
console.log( typeof symbol ); // "symbol"

5. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
// Option 1:
var firstName = Symbol("first name");
var person = {};
person[firstName] = "Eyal";
// Option 2:
var person = {
[firstName] : "Eyal"
};
// Option 3:
// make the property read only
Object.defineProperty( person, firstName, { writable: false } );

6. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com

7. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com

8. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com

9. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
class Person{
constructor(name){
this.name = name;
}
[Symbol.toStringTag](){
return "Person";
}
toString(){
return this.name;
}
}
var me = new Person("Eyal Vardi");
console.log(me.toString()); // Eyal Vardi
console.log(Object.prototype.toString.call(me)); // Person

10. © 2015 Eyal Vardi. All rights reserved. Tel: 054-5-767-300, Email: evardi@gmail.com
http://www.2ality.com/
Understanding ECMAScript 6
http://ecmascript6.org/
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Harmony specification_drafts

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