javascript - Include new parameter in object literal and retrieve

Question

javascript - Include new parameter in object literal and retrieve

I have a base object that I define using an object literal:

var obj = {
   key1   : 'value1',
   key2   : 'value2'
}

Now, I want to pass this object to a function and extend it like this:

myFunction( obj + { key3 : 'value3' } );

// The parameter will be:
{
   key1   : 'value1',
   key2   : 'value2',
   key3   : 'value3'
}

or

myFunction( obj + { key2 : 'new value2' } );

// The parameter will be:
{
   key1   : 'value1',
   key2   : 'new value2'
}

The use of the + operator in this context is not correct. Is there a way to achieve this?

EDIT: Do you want to permanently alter obj? - No, I would like to be able to reuse it as a base for the next call.

javascript object

Answer 1

Answer №1

Utilizing the object spread syntax available in ES2018 or TypeScript 2.1 allows you to easily manage properties in objects.

// Properties on the right update properties on the left
// Overwrite properties from obj
myFunction( { ...obj, key3: 'value3' } );
// Don't overwrite properties from obj
myFunction( { key3: 'value3', ...obj } );

For those using ES2015, the Object.assign method serves a similar purpose.

// Object.assign(a, b, c, ..) - copy properties from b to a, then from c to a etc.
// Overwrite properties from obj
myFunction( Object.assign({}, obj, { key3: 'value3' }) );
// Don't overwrite properties from obj
myFunction( Object.assign({ key3: 'value3' }, obj) );

Check out a demonstration here.

var obj = { key1: 'value1', key2: 'value2'}
console.log('-- Object Spread --');
console.log({ ...obj, key3: 'value3' });
console.log('overwrite');
console.log({ ...obj, key2: 'NEW2' });
console.log('no overwrite');
console.log({ key2: 'NEW2', ...obj });

console.log('-- Object Assign --');
console.log(Object.assign({ key3: 'value3' }, obj));
console.log('overwrite');
console.log(Object.assign({}, obj, { key2: 'NEW2' }));
console.log('no overwrite');
console.log(Object.assign({ key2: 'NEW2' }, obj));

console.log('-- Original Object unchanged --');
console.log(obj);

Answer 2

Utilizing the object spread syntax available in ES2018 or TypeScript 2.1 allows you to easily manage properties in objects.

// Properties on the right update properties on the left
// Overwrite properties from obj
myFunction( { ...obj, key3: 'value3' } );
// Don't overwrite properties from obj
myFunction( { key3: 'value3', ...obj } );

For those using ES2015, the Object.assign method serves a similar purpose.

// Object.assign(a, b, c, ..) - copy properties from b to a, then from c to a etc.
// Overwrite properties from obj
myFunction( Object.assign({}, obj, { key3: 'value3' }) );
// Don't overwrite properties from obj
myFunction( Object.assign({ key3: 'value3' }, obj) );

Check out a demonstration here.

var obj = { key1: 'value1', key2: 'value2'}
console.log('-- Object Spread --');
console.log({ ...obj, key3: 'value3' });
console.log('overwrite');
console.log({ ...obj, key2: 'NEW2' });
console.log('no overwrite');
console.log({ key2: 'NEW2', ...obj });

console.log('-- Object Assign --');
console.log(Object.assign({ key3: 'value3' }, obj));
console.log('overwrite');
console.log(Object.assign({}, obj, { key2: 'NEW2' }));
console.log('no overwrite');
console.log(Object.assign({ key2: 'NEW2' }, obj));

console.log('-- Original Object unchanged --');
console.log(obj);

Answer 3

Answer №2

To modify obj, simply adjust it before passing it:

var obj = { /* data */ };

obj.key3 = 'value3';
myFunction(obj);

Do you wish to permanently change obj? - No, I would like to reuse it for the next call as a base.

If that's the case, you will need to create a copy of obj and modify the copy — either before calling myFunction:

var obj = { /* data */ };
var extension = {key3: 'value3'};

myFunction($.extend({}, obj, extension));

or provide both obj and the "extension" to myFunction:

var obj = { /* data */ };
var extension = {key3: 'value3'};

myFunction(obj, extension);

and let myFunction handle the task:

function myFunction(base, ext)
{
    if (typeof base === 'object' && typeof ext === 'object')
    {
        base = $.extend({}, base, ext);
    }

    // add remaining function logic here
}

If you are already using jQuery or don't mind using it, $.extend() can be very helpful for this purpose.

Answer 4

To modify obj, simply adjust it before passing it:

var obj = { /* data */ };

obj.key3 = 'value3';
myFunction(obj);

Do you wish to permanently change obj? - No, I would like to reuse it for the next call as a base.

If that's the case, you will need to create a copy of obj and modify the copy — either before calling myFunction:

var obj = { /* data */ };
var extension = {key3: 'value3'};

myFunction($.extend({}, obj, extension));

or provide both obj and the "extension" to myFunction:

var obj = { /* data */ };
var extension = {key3: 'value3'};

myFunction(obj, extension);

and let myFunction handle the task:

function myFunction(base, ext)
{
    if (typeof base === 'object' && typeof ext === 'object')
    {
        base = $.extend({}, base, ext);
    }

    // add remaining function logic here
}

If you are already using jQuery or don't mind using it, $.extend() can be very helpful for this purpose.

Answer 5

Answer №3

If you want to enhance objects without modifying the original one, you can create a function to do so. Here's an example:

var originalObject = {name: 'foo'};

function extendNonDestructive(source, newProperties) {
  function Temp() {} 
  Temp.prototype = source;
  var newObj = new Temp;
  for (var prop in newProperties) {
    if (newProperties.hasOwnProperty(prop)) {
      newObj[prop] = newProperties[prop]
    }
  }
  return newObj
}

var enhancedObject = extendNonDestructive(originalObject, {lastName: 'bar'}); // Does not alter originalObject

Keep in mind that there is also Object.create, which provides more flexibility compared to the method used in my code snippet, but it requires ES5 or newer.

Answer 6

If you want to enhance objects without modifying the original one, you can create a function to do so. Here's an example:

var originalObject = {name: 'foo'};

function extendNonDestructive(source, newProperties) {
  function Temp() {} 
  Temp.prototype = source;
  var newObj = new Temp;
  for (var prop in newProperties) {
    if (newProperties.hasOwnProperty(prop)) {
      newObj[prop] = newProperties[prop]
    }
  }
  return newObj
}

var enhancedObject = extendNonDestructive(originalObject, {lastName: 'bar'}); // Does not alter originalObject

Keep in mind that there is also Object.create, which provides more flexibility compared to the method used in my code snippet, but it requires ES5 or newer.

Answer 7

Answer №4

To easily add properties to an existing object and return the new object in one line, you can leverage both the Object.fromEntries and Object.entries functions:

console.log(
   Object.fromEntries(
    Object.entries({
      t:4,
      f:2
    })
    .concat(
      Object.entries({
            q:2,
            p:9
      })
    )
  )
);

This method also works well if you only need to modify a single property of an existing object. Simply add the object with the updated property to replace it, for example:

....concat(Object.entries({t:2}))...

This approach will specifically change the value of the t property within the original object.

Answer 8

To easily add properties to an existing object and return the new object in one line, you can leverage both the Object.fromEntries and Object.entries functions:

console.log(
   Object.fromEntries(
    Object.entries({
      t:4,
      f:2
    })
    .concat(
      Object.entries({
            q:2,
            p:9
      })
    )
  )
);

This method also works well if you only need to modify a single property of an existing object. Simply add the object with the updated property to replace it, for example:

....concat(Object.entries({t:2}))...

This approach will specifically change the value of the t property within the original object.

javascript - Include new parameter in object literal and retrieve

Answer №1

Answer №2

Answer №3

Answer №4

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