Create a nickname for a property in JavaScript

Question

Create a nickname for a property in JavaScript

It seems like a straightforward question,

Is there an easy method to create an alternate name for a property (I believe this one is specific to String – but I'm not entirely sure), for example

a = length // this line is pseudo code

'hello world'.length // returns 11
'hello world'.a      // this line is pseudo code, meant to return 11

In the scenario above, a synonym is being introduced for the property length. Is it feasible to achieve in JavaScript?

javascript variables properties

Answer 1

Answer №1

1. Accessing Properties with Bracket Notation

Using bracket notation, you can access properties in the following way:

'hello world'[c]

If the variable c is set to 'length', then this line of code is equivalent to 'hello world'.length.

var c = 'length';
console.log('hello world'[c]);

The main distinction here is that the property name is passed as a string when using bracket notation. It serves as a property accessor.

2. Using Object.defineProperty() for Creating Aliases

If you want to create an alias, you can do so by:

Object.defineProperty(String.prototype, 'c', {
    get: function() {
        return this.length;
    }
});

console.log("hello world".c);

In the above example, Object.defineProperty is used to define a new property for the String object's prototype. Subsequently, all instances of strings will have access to this new property. As explained in the documentation:

The Object.defineProperty() method either adds a new property to an object or modifies an existing one, and returns the updated object.

Syntax
Object.defineProperty(obj, prop, descriptor)

In this context, obj refers to the target object being modified, prop denotes the property being added or modified, and descriptor outlines the characteristics of the property.

Hence, in the given scenario, a property named c is defined for String.prototype where its descriptor includes a getter function that returns the length of the current string instance. By utilizing getters, it ensures dynamic retrieval of property values based on specific conditions. More details on getters can be found here.

This approach can be extended to other types by adjusting the target prototype (obj). For instance, using Object.prototype allows for defining properties at a broader level. Nonetheless, caution must be exercised as attempting to retrieve this.length from an object lacking a length property would yield undefined results, illustrated here. Alternatively, Object.defineProperties offers a way to define multiple properties simultaneously.

Answer 2

1. Accessing Properties with Bracket Notation

Using bracket notation, you can access properties in the following way:

'hello world'[c]

If the variable c is set to 'length', then this line of code is equivalent to 'hello world'.length.

var c = 'length';
console.log('hello world'[c]);

The main distinction here is that the property name is passed as a string when using bracket notation. It serves as a property accessor.

2. Using Object.defineProperty() for Creating Aliases

If you want to create an alias, you can do so by:

Object.defineProperty(String.prototype, 'c', {
    get: function() {
        return this.length;
    }
});

console.log("hello world".c);

In the above example, Object.defineProperty is used to define a new property for the String object's prototype. Subsequently, all instances of strings will have access to this new property. As explained in the documentation:

The Object.defineProperty() method either adds a new property to an object or modifies an existing one, and returns the updated object.

Syntax
Object.defineProperty(obj, prop, descriptor)

In this context, obj refers to the target object being modified, prop denotes the property being added or modified, and descriptor outlines the characteristics of the property.

Hence, in the given scenario, a property named c is defined for String.prototype where its descriptor includes a getter function that returns the length of the current string instance. By utilizing getters, it ensures dynamic retrieval of property values based on specific conditions. More details on getters can be found here.

This approach can be extended to other types by adjusting the target prototype (obj). For instance, using Object.prototype allows for defining properties at a broader level. Nonetheless, caution must be exercised as attempting to retrieve this.length from an object lacking a length property would yield undefined results, illustrated here. Alternatively, Object.defineProperties offers a way to define multiple properties simultaneously.

Answer 3

Answer №2

Building upon the response from @AndrewLi, there are various ways to create alias-like functionalities using Object.defineProperty().

Read-only alias (similar to Andrew's explanation)
Synced alias updates the source when modified
Defaulted alias reads or defaults to the source until changed (breaking the relationship at that point)

To illustrate, let's define functions that establish a connection between a source object with property sProp, and a target object with property tProp. It's possible for the source and target to be the same object, but this is not mandatory. Additionally, either the source or target can be a prototype like Object.prototype or String.prototype.

"Normal" assignment approach

This method does not function as an alias and doesn't utilize Object.defineProperty(). Instead, it assigns the VALUE of the source to the target. Therefore, changes in the source do not affect the target.

function assign(target, tProp, source, sProp) {
  target[tProp] = source[sProp];
  return target;
}

let myTarget = {}
let mySource = {b: 12}

myTarget = assign(myTarget, 'a', mySource, 'b')

// Value from source assigned to "alias"
console.log('"alias":',myTarget.a) // 12

// Changes in source don't impact "alias"
mySource.b = 13
console.log("source:", mySource.b) // 13
console.log('"alias":', myTarget.a) // still 12

Creating a Read-only Alias (based on the above solution)

A read-only alias results when a property definition lacks a setter, rendering its value unchangeable. Modifications in the source property reflect in the alias, but you cannot set a new value to the alias.

function read(target, tProp, source, sProp){
  Object.defineProperty(target, tProp, {
    enumerable: true,
    configurable: true,
    get(){
      return source[sProp];
    }
  })
  return target;
}

let myTarget = {}
let mySource = {b: 12}

myTarget = read(myTarget, 'a', mySource, 'b')

// Alias fetches value from source
console.log("alias:", myTarget.a) // 12

// The absence of a setter enforces read-only nature
myTarget.a = 15
console.log("alias:", myTarget.a) // 12

// Source modifications reflected in the target
mySource.b = 15
console.log("source:", mySource.b) //15
console.log("target:", myTarget.a) //15

Designing a Synced Alias

This type of alias enhances the read-only version by updating the source property whenever the alias property changes. Consequently, both the source and target always stay synchronized.

function sync(target, tProp, source, sProp){
  Object.defineProperty(target, tProp, {
    enumerable: true,
    configurable: true,
    get(){
      return source[sProp];
    },
    set(value){
      source[sProp] = value;
    }
  })
  return target;
}

let myTarget = {}
let mySource = {b: 12}

myTarget = sync(myTarget, 'a', mySource, 'b')

// Alias obtains value from source
console.log("alias:", myTarget.a) // 12

// Changing alias updates the source
myTarget.a = 15
console.log("alias:", myTarget.a) // 15
console.log("source:", mySource.b) // 15

// Altering source reflects in the alias
mySource.b = 20
console.log("source:", mySource.b) // 20
console.log("alias:", myTarget.a) // 20

Using Alias as Default

This functionality allows setting a default value to the alias/target until manually updated. Unlike the read-only scenario, you can change the alias/target value. However, unlike the synced alias, modifying the alias won't propagate changes to the source - instead, the alias becomes a regular value.

function setDefault(target, tProp, source, sProp){
  Object.defineProperty(target, tProp, {
    enumerable: true,
    configurable: true,
    get(){
      return source[sProp];
    },
    set(value){
      delete target[tProp];
      target[tProp] = value;
    }
  })
  return target;
}

let myTarget = {}
let mySource = {b: 12}

myTarget = setDefault(myTarget, 'a', mySource, 'b')

// Alias acquires value from source
console.log('alias:', myTarget.a) // 12

// Updates in source affect the alias
mySource.b = 15
console.log('source:', mySource.b) // 15
console.log('alias:', myTarget.a) // 15

// Altering the alias DOES NOT modify the source
myTarget.a = 20
console.log("alias:", myTarget.a) // 20
console.log("source:", mySource.b) // 15

// The linkage between source and alias breaks here
mySource.b = 100
console.log("source:", mySource.b) // 100
console.log("alias:", myTarget.a) // 20

Answer 4

Building upon the response from @AndrewLi, there are various ways to create alias-like functionalities using Object.defineProperty().

Read-only alias (similar to Andrew's explanation)
Synced alias updates the source when modified
Defaulted alias reads or defaults to the source until changed (breaking the relationship at that point)

To illustrate, let's define functions that establish a connection between a source object with property sProp, and a target object with property tProp. It's possible for the source and target to be the same object, but this is not mandatory. Additionally, either the source or target can be a prototype like Object.prototype or String.prototype.

"Normal" assignment approach

This method does not function as an alias and doesn't utilize Object.defineProperty(). Instead, it assigns the VALUE of the source to the target. Therefore, changes in the source do not affect the target.

function assign(target, tProp, source, sProp) {
  target[tProp] = source[sProp];
  return target;
}

let myTarget = {}
let mySource = {b: 12}

myTarget = assign(myTarget, 'a', mySource, 'b')

// Value from source assigned to "alias"
console.log('"alias":',myTarget.a) // 12

// Changes in source don't impact "alias"
mySource.b = 13
console.log("source:", mySource.b) // 13
console.log('"alias":', myTarget.a) // still 12

Creating a Read-only Alias (based on the above solution)

A read-only alias results when a property definition lacks a setter, rendering its value unchangeable. Modifications in the source property reflect in the alias, but you cannot set a new value to the alias.

function read(target, tProp, source, sProp){
  Object.defineProperty(target, tProp, {
    enumerable: true,
    configurable: true,
    get(){
      return source[sProp];
    }
  })
  return target;
}

let myTarget = {}
let mySource = {b: 12}

myTarget = read(myTarget, 'a', mySource, 'b')

// Alias fetches value from source
console.log("alias:", myTarget.a) // 12

// The absence of a setter enforces read-only nature
myTarget.a = 15
console.log("alias:", myTarget.a) // 12

// Source modifications reflected in the target
mySource.b = 15
console.log("source:", mySource.b) //15
console.log("target:", myTarget.a) //15

Designing a Synced Alias

This type of alias enhances the read-only version by updating the source property whenever the alias property changes. Consequently, both the source and target always stay synchronized.

function sync(target, tProp, source, sProp){
  Object.defineProperty(target, tProp, {
    enumerable: true,
    configurable: true,
    get(){
      return source[sProp];
    },
    set(value){
      source[sProp] = value;
    }
  })
  return target;
}

let myTarget = {}
let mySource = {b: 12}

myTarget = sync(myTarget, 'a', mySource, 'b')

// Alias obtains value from source
console.log("alias:", myTarget.a) // 12

// Changing alias updates the source
myTarget.a = 15
console.log("alias:", myTarget.a) // 15
console.log("source:", mySource.b) // 15

// Altering source reflects in the alias
mySource.b = 20
console.log("source:", mySource.b) // 20
console.log("alias:", myTarget.a) // 20

Using Alias as Default

This functionality allows setting a default value to the alias/target until manually updated. Unlike the read-only scenario, you can change the alias/target value. However, unlike the synced alias, modifying the alias won't propagate changes to the source - instead, the alias becomes a regular value.

function setDefault(target, tProp, source, sProp){
  Object.defineProperty(target, tProp, {
    enumerable: true,
    configurable: true,
    get(){
      return source[sProp];
    },
    set(value){
      delete target[tProp];
      target[tProp] = value;
    }
  })
  return target;
}

let myTarget = {}
let mySource = {b: 12}

myTarget = setDefault(myTarget, 'a', mySource, 'b')

// Alias acquires value from source
console.log('alias:', myTarget.a) // 12

// Updates in source affect the alias
mySource.b = 15
console.log('source:', mySource.b) // 15
console.log('alias:', myTarget.a) // 15

// Altering the alias DOES NOT modify the source
myTarget.a = 20
console.log("alias:", myTarget.a) // 20
console.log("source:", mySource.b) // 15

// The linkage between source and alias breaks here
mySource.b = 100
console.log("source:", mySource.b) // 100
console.log("alias:", myTarget.a) // 20

Create a nickname for a property in JavaScript

Answer №1

Answer №2

"Normal" assignment approach

Creating a Read-only Alias (based on the above solution)

Designing a Synced Alias

Using Alias as Default

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