Symbols as Property Names

Introduction to Symbols in JavaScript

Hey there! Let us explore the JavaScript Symbolic universe. Thus, if you haven't heard, symbols—which appear with ECMAScript 6 (ES6)—are rather new faces in the JavaScript landscape. See them as these special little markers for object properties for which you have no need to concern yourself with conflict with anything else.

What distinguishes them?

Unlike your regular numbers, strings, or booleans, they are their own sort of data type.
All you have to do to design a symbol is call the Symbol function. Every time you do, it brilliantly spits out a unique sign!
This is quite helpful when you wish to keep your property keys unique and prevent unintentionally trespassing on other properties down the road.

Symbols in JavaScript are not only another addition to the family of data types in grand plan. Actually, they provide fresh interesting approaches for us to consider how we manage object property keys. Great, right?

Understanding Property Names in JavaScript

Now let's dissect JavaScript's property name behavior. See objects as small, well defined boxes of stuff—properties. Every one of these qualities bears a name and a value. These attributes can now be named with almost any string you choose, even an empty one. There are certain oddities, though, when you mix numbers or special characters.


let obj = {
  "": "This is an empty string property name",
  "123": "This is a numeric string property name",
  "!@#$%^&*()": "This is a special character string property name"
};

Look at that code upstairs! We have ourselves an object with three peculiar qualities. Though they all have a string as their name, they are somewhat different:

The property name is empty first of all. Sounds strange, huh? Still, it's quite reasonable.
We have then a numerical string. Though it seems like a number, in this context it's simply a normal ol' string.
At last we have some unique characters strung together. Indeed still a legal property name, believe it or not!

The worst part is that the normal dot notation won't cut it if you wish to visit these sites. You must so follow bracket notation rather.


console.log(obj[""]); // Outputs: This is an empty string property name
console.log(obj["123"]); // Outputs: This is a numeric string property name
console.log(obj["!@#$%^&*()"]); // Outputs: This is a special character string property name

View what is going here. We peep at the object characteristics using bracket notation. Dot notation only loves valid JavaScript IDs, hence it is useless here. And here, friend, is where symbols really shine. Sometimes it's quite helpful to be able to name property using non-string values.

How to Use Symbols as Property Names

Starting utilizing symbols for JavaScript's property names? Really, it's quite basic. You'll first call the Symbol function to generate a symbol. You might then name a property in your object using this brilliant new symbol.


let mySymbol = Symbol();
let obj = {};
obj[mySymbol] = "Hello, World!";

See that fragment above? First we create mySymbol, a symbol. Our next creation is an empty object called obj. At last, we give this object a property under mySymbol's name and "Hello, World!" for value. Just employ the symbol with bracket notation to reach the worth of this property.


console.log(obj[mySymbol]); // Outputs: Hello, World!

Here, then, we are obtaining the value from obj using mySymbol. Dot notation won't work with symbol keys, remember!

Notable Knowledge:

Symbols want to be low profile. They won't show up in loops for... Try Object.getOwnPropertySymbol() if you are on a symbol hunt.
Want a JSON string from an object with symbols? Regarding symbols, JSON.stringify() is going to treat you with cold shoulder. For that you would require your own game plan.


console.log(Object.getOwnPropertySymbols(obj)); // Outputs: [ Symbol() ]
console.log(JSON.stringify(obj)); // Outputs: {}

Object.getOwn Property Symbols(obj) provides you a list of all object symbol properties in that fragment. Indeed, JSON.stringify(obj) returns empty since it ignores the symbol properties.

Benefits of Using Symbols as Property Names

Why waste symbols for JavaScript property names? Well, they offer some quite clever features!


let symbol1 = Symbol('mySymbol');
let symbol2 = Symbol('mySymbol');
console.log(symbol1 === symbol2); // Outputs: false

Looking at that code above, consider Two symbols with the same label still differ like night and day even if you whirl them together. Right there, that is some very distinct quality.


let mySymbol = Symbol();
let obj = {
  [mySymbol]: "Hello, World!",
  notASymbol: "Hi, Universe!"
};
console.log(Object.keys(obj)); // Outputs: ['notASymbol']

Also low profile are symbols. Calling Object.keys will merely provide the ordinary, non-symbol keys. Ideal for when you want to keep something covert and underactive.


let iterableObj = {
  [Symbol.iterator]() {
    let step = 0;
    let iterator = {
      next() {
        step++;
        if (step <= 3) {
          return { value: step, done: false };
        } else {
          return { value: undefined, done: true };
        }
      }
    };
    return iterator;
  }
};

for (let value of iterableObj) {
  console.log(value); // Outputs: 1, then 2, then 3
}

Perks of Symbols:

Uniqueness: One of a kind every symbol is unique. Use them as property names, and you won’t have to worry about other properties stepping on their toes. Even if you create symbols with the same description, they're unique.
Privacy: By default, symbols stay out of for...in loops and Object.keys() calls. Handy for keeping certain details hidden away. See how Object.keys(obj) only spits out the non-symbol property?
Well-known Symbols: JavaScript comes with its own set of built-in symbols that let you tweak how things usually work under the hood. Take Symbol.iterator for example—it makes objects like iterableObj iterable. The for...of loop then effortlessly steps through each value.

Practical Examples of Symbols as Property Names

Alright, let's explore some actual situations where symbols can greatly simplify your life as property names. Imagine you are building a library and wish to include some hidden ingredients—properties—into objects your users will be producing. Nonetheless, yikes! You really don't want these secret sauce qualities conflicting with whatever the consumers choose to add. Now enter: symbols!


let librarySymbol = Symbol('libraryProperty');

function LibraryObject() {
  this[librarySymbol] = 'This is a library property';
}

let userObject = new LibraryObject();
userObject.userProperty = 'This is a user property';

console.log(userObject.userProperty); // Outputs: This is a user property
console.log(userObject[librarySymbol]); // Outputs: This is a library property

What is occurring there? LibrarySymbol is working magic as a property name within LibraryObject. Being a symbol, it's chillin'—not stressing about running over user-added properties. Symbols to come to save us!

Still another cool use for it.

Suppose you have to slip some metadata—performance notes, debugging details, whatever floats your boat—into objects without drawing attention. symbols to save once more!


let debugSymbol = Symbol('debugInfo');

function MyObject() {
  this.someProperty = 'Hello, World!';
  this[debugSymbol] = 'This object was created at ' + new Date();
}

let obj = new MyObject();

console.log(obj.someProperty); // Outputs: Hello, World!
console.log(obj[debugSymbol]); // Outputs: This object was created at ...

See that! DebugSymbol serves two purposes: it is a property name used in sneaking in debugging information. And as it's a symbol, only those with knowledge can spot the hidden elements. How neat is it not going to clutter any for...in loops or get mentioned in Object.keys()?

Common Mistakes When Using Symbols as Property Names

While playing with symbols as property names in JavaScript is super cool, it’s easy to trip up if you’re not careful. These are some typical mistakes programmers create:

Assuming symbols represent strings: It's a classic mistake: believing that strings and symbols are friends. Shortcut: they aren't. Trying to mix symbols with strings, like in concatenation, will not end well.


    let mySymbol = Symbol('mySymbol');
    console.log('Symbol is: ' + mySymbol); // Throws TypeError: Cannot convert a Symbol value to a string

Oh, sorry! A symbol isn't going to morph into a string for you, so that code throws TypeError. Give spin to string if you need it as a string.

Another trip-up: Using the same description for several symbols? Expecting symbols with the same description to match up like long-lost twins.


    let symbol1 = Symbol('mySymbol');
    let symbol2 = Symbol('mySymbol');
    console.log(symbol1 === symbol2); // Outputs: false

Notice how even with the same description, our two symbols aren’t seeing eye to eye? That’s because every Symbol() call churns out a unique result!

Expecting Symbol Properties to be Enumerable: Imagining symbol properties are going to pop up like daisies in for...in loops or when using Object.keys() just isn’t going to happen.


    let mySymbol = Symbol();
    let obj = {
      [mySymbol]: "Hello, World!",
      notASymbol: "Hi, Universe!"
    };
    console.log(Object.keys(obj)); // Outputs: [ 'notASymbol' ]

See indeed. No symbol properties in sight with Object.keys(). If you want to round up all those symbols, Object.getOwnPropertySymbols() is your friend!

Advanced Concepts: Well-Known Symbols

Entering the deep end, JavaScript transcends basic symbols. Prepare to meet the well-known symbols; these built-in ones include powers that can modify the default behavior of your objects. Right there on the Symbol object, they are freezing, just waiting for action!

Using this one, which lets you work magic with for...of loops, an object becomes iterable like the secret sauce.


let iterableObj = {
  [Symbol.iterator]() {
    let step = 0;
    let iterator = {
      next() {
        step++;
        if (step <= 3) {
          return { value: step, done: false };
        } else {
          return { value: undefined, done: true };
        }
      }
    };
    return iterator;
  }
};

for (let value of iterableObj) {
  console.log(value); // Outputs: 1, then 2, then 3
}

Symbol.iterator turns iterable obj into something you might easily loop over in this bit. Pulling the values from the iterator, the for...of completes the remainder.
Symbol.toStringTag: Ever wanted to change what you saw when you execute toString() on an object? Symbol.toString Tag Right now you can!
```
let myObj = {
  [Symbol.toStringTag]: 'MyObject'
};

console.log(myObj.toString()); // Outputs: [object MyObject]
        
```
Here, Symbol.toString Tag is being used to vary the outcome of my obj.toString(), therefore allowing you brand the object anyway you desire!

Symbol.species: Imagine being able to control the kind of object your classes produce, and you will find great appeal in this symbol.


class MyArray extends Array {
  static get [Symbol.species]() {
    return Array;
  }
}

let myArray = new MyArray(1, 2, 3);
let derivedArray = myArray.map(x => x * x);

console.log(derivedArray instanceof MyArray); // Outputs: false
console.log(derivedArray instanceof Array); // Outputs: true

Symbol.species guarantees in the preceding example that the map method puts back a standard array rather than a MyArray. Complete authority over return forms!

Comparison: Symbols vs Strings as Property Names

There is plenty to consider while choosing between symbols and strings for JavaScript's property names. Let's see how they rank against one another.

Uniqueness: Symbols are all about originality. Two symbols are utterly different even if they have the same meaning. Not so with strings; if they seem the same, they are deemed to be equal.


let symbol1 = Symbol('mySymbol');
let symbol2 = Symbol('mySymbol');
console.log(symbol1 === symbol2); // Outputs: false

let string1 = 'myString';
let string2 = 'myString';
console.log(string1 === string2); // Outputs: true

Enumerability: Symbol properties are by default like ninjas; they don't show up in for...in loops or with Object.keys(). Still, strings are more obvious and visible.


let mySymbol = Symbol();
let obj = {
  [mySymbol]: "Hello, World!",
  notASymbol: "Hi, Universe!"
};
console.log(Object.keys(obj)); // Outputs: [ 'notASymbol' ]

Privacy: Would you like some down-low properties kept under reserve? Given their non-enumerable character, symbol properties are your buddy for confidential data. Strings? Not so much; they resemble having a sign pointing to your land.


let privateSymbol = Symbol();
let obj = {
  [privateSymbol]: "This is a private property",
  publicProperty: "This is a public property"
};
console.log(obj.publicProperty); // Outputs: This is a public property
console.log(obj[privateSymbol]); // Outputs: This is a private property

Well-known Symbols: JavaScript provides us unique built-in symbols to customize default behavior of objects. Strings lack a comparable cool feature right now.

Thus, what is the decision? Symbols are your first choice if you yearn for originality, quiet, or customizing defaults. But strings can be your best choice if you're looking for something like enumerability or just want things simple.

Best Practices for Using Symbols as Property Names

While experimenting with symbols as property names in JavaScript to aid to slightly ease your coding life, keep in mind many best practices.

Use explanations for debugging; Consider adding an explanation as you design a symbol. JavaScript does not make advantage of it; but, you will thank yourself when debugging.


    let mySymbol = Symbol('mySymbol');
    console.log(mySymbol.toString()); // Outputs: Symbol(mySymbol)

See there? MySymbol.toString() shows the word "mySymbol". Like leaving a small debugging breadcrumb trail.

Use Symbols for Private Properties: Use symbols for private properties since they are rather useful for hiding and fitting for your belongings.


    let privateSymbol = Symbol();
    let obj = {
      [privateSymbol]: "This is a private property",
      publicProperty: "This is a public property"
    };

Here we quietly add private property into obj using a private symbol. Though not obvious, it is there!

Using well-known symbols Smartly: JavaScript offers several well-known symbols that could affect the running of particular activities. Use them sparingly; they are potent and will influence the running of your code.


    let iterableObj = {
      [Symbol.iterator]() {
        // ...
      }
    };

This section makes iterable objects iterable using Symbol.iterator, therefore altering the way for...of loops and other iterator-friendly operations work.
Remember That Symbols Are Not Strings: Though they look to be strings, symbols are a different kettle of fish entirely. Never forget this.
```
    let mySymbol = Symbol('mySymbol');
    console.log('Symbol is: ' + mySymbol); // Throws TypeError: Cannot convert a Symbol value to a string
    
```
A little reminder: symbols and strings aren’t interchangeable, so mixing them up can lead to errors like the TypeError above.

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