Delete field in object javascript

delete operator

The delete operator removes a property from an object. If the property’s value is an object and there are no more references to the object, the object held by that property is eventually released automatically.

Try it

Syntax

delete object.property delete object[property] 

Note: The syntax allows a wider range of expressions following the delete operator, but only the above forms lead to meaningful behaviors.

Parameters

The name of an object, or an expression evaluating to an object.

Return value

true for all cases except when the property is an own non-configurable property, in which case false is returned in non-strict mode.

Exceptions

Thrown in strict mode if the property is an own non-configurable property.

Description

The delete operator has the same precedence as other unary operators like typeof . Therefore, it accepts any expression formed by higher-precedence operators. However, the following forms lead to early syntax errors in strict mode:

delete identifier; delete object.#privateProperty; 

Because classes are automatically in strict mode, and private properties can only be legally referenced in class bodies, this means private properties can never be deleted. While delete identifier may work if identifier refers to a configurable property of the global object, you should avoid this form and prefix it with globalThis instead.

While other expressions are accepted, they don’t lead to meaningful behaviors:

delete console.log(1); // Logs 1, returns true, but nothing deleted 

The delete operator removes a given property from an object. On successful deletion, it will return true , else false will be returned. Unlike what common belief suggests (perhaps due to other programming languages like delete in C++), the delete operator has nothing to do with directly freeing memory. Memory management is done indirectly via breaking references. See the memory management page for more details.

It is important to consider the following scenarios:

• If the property which you are trying to delete does not exist, delete will not have any effect and will return true .
• delete only has an effect on own properties. If a property with the same name exists on the object’s prototype chain, then after deletion, the object will use the property from the prototype chain.
• Non-configurable properties cannot be removed. This includes properties of built-in objects like Math , Array , Object and properties that are created as non-configurable with methods like Object.defineProperty() .
• Deleting variables, including function parameters, never works. delete variable will throw a SyntaxError in strict mode, and will have no effect in non-strict mode.
  • Any variable declared with var cannot be deleted from the global scope or from a function’s scope, because while they may be attached to the global object, they are not configurable.
  • Any variable declared with let or const cannot be deleted from the scope within which they were defined, because they are not attached to an object.

  Examples

  Using delete

  Note: The following example uses non-strict-mode only features, like implicitly creating global variables and deleting identifiers, which are forbidden in strict mode.

  // Creates the property empCount on the global scope. // Since we are using var, this is marked as non-configurable. var empCount = 43; // Creates the property EmployeeDetails on the global scope. // Since it was defined without "var", it is marked configurable. EmployeeDetails =  name: "xyz", age: 5, designation: "Developer", >; // delete can be used to remove properties from objects. delete EmployeeDetails.name; // returns true // Even when the property does not exist, delete returns "true". delete EmployeeDetails.salary; // returns true // EmployeeDetails is a property of the global scope. delete EmployeeDetails; // returns true // On the contrary, empCount is not configurable // since var was used. delete empCount; // returns false // delete also does not affect built-in static properties // that are non-configurable. delete Math.PI; // returns false function f()  var z = 44; // delete doesn't affect local variable names delete z; // returns false > 

  delete and the prototype chain

  In the following example, we delete an own property of an object while a property with the same name is available on the prototype chain:

  function Foo()  this.bar = 10; > Foo.prototype.bar = 42; const foo = new Foo(); // foo.bar is associated with the // own property. console.log(foo.bar); // 10 // Delete the own property within the // foo object. delete foo.bar; // returns true // foo.bar is still available in the // prototype chain. console.log(foo.bar); // 42 // Delete the property on the prototype. delete Foo.prototype.bar; // returns true // The "bar" property can no longer be // inherited from Foo since it has been // deleted. console.log(foo.bar); // undefined 

  Deleting array elements

  When you delete an array element, the array length is not affected. This holds even if you delete the last element of the array.

  When the delete operator removes an array element, that element is no longer in the array. In the following example, trees[3] is removed with delete .

  const trees = ["redwood", "bay", "cedar", "oak", "maple"]; delete trees[3]; console.log(3 in trees); // false 

  This creates a sparse array with an empty slot. If you want an array element to exist but have an undefined value, use the undefined value instead of the delete operator. In the following example, trees[3] is assigned the value undefined , but the array element still exists:

  const trees = ["redwood", "bay", "cedar", "oak", "maple"]; trees[3] = undefined; console.log(3 in trees); // true 

  If instead, you want to remove an array element by changing the contents of the array, use the splice() method. In the following example, trees[3] is removed from the array completely using splice() :

  const trees = ["redwood", "bay", "cedar", "oak", "maple"]; trees.splice(3, 1); console.log(trees); // ["redwood", "bay", "cedar", "maple"] 

  Deleting non-configurable properties

  When a property is marked as non-configurable, delete won’t have any effect, and will return false . In strict mode, this will raise a TypeError .

  const Employee = >; Object.defineProperty(Employee, "name",  configurable: false >); console.log(delete Employee.name); // returns false 

  var creates non-configurable properties that cannot be deleted with the delete operator:

  // Since "nameOther" is added using with the // var keyword, it is marked as non-configurable var nameOther = "XYZ"; // We can access this global property using: Object.getOwnPropertyDescriptor(globalThis, "nameOther"); // // value: "XYZ", // writable: true, // enumerable: true, // configurable: false // > delete globalThis.nameOther; // return false 

  In strict mode, this would raise an exception.

  Deleting global properties

  If a global property is configurable (for example, via direct property assignment), it can be deleted, and subsequent references to them as global variables will produce a ReferenceError .

  .globalVar = 1; console.log(globalVar); // 1 // In non-strict mode, you can use `delete globalVar` as well delete globalThis.globalVar; console.log(globalVar); // ReferenceError: globalVar is not defined 

  Specifications

  Browser compatibility

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  See also

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  This page was last modified on Jun 7, 2023 by MDN contributors.

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  Источник

  How to Remove a Property from a JavaScript Object?

  

  JavaScript objects contain properties that can be deleted if required. There are three ways using which we can easily delete any property of the object. The first way is using the special operator in JavaScript called the delete operator, the second way is using Object Destructuring and the third one is using the Reflect.deleteProperty() method.

  Introduction

  JavaScript Objects consist of properties that are just the combination of keys and values. In short, properties have pair of keys and values that can be of any kind of entity. Even functions can also act as a key or as a value in any Object. Anyway, here, we are going to discuss how can we remove key from Object JavaScript.

  Removing a key automatically removes the value associated with that key. Hence, removing a key is nothing but removing that property itself. Now, there are three ways to remove key from object in JavaScript. Let us have a brief look over all of them.

  1. Remove a Property from a JavaScript Object using the Delete Operator

  There is a special operator in JavaScript called the delete operator which can be used to remove a key from Object JavaScript. As the name suggests, the delete operator simply deletes the specified property from the object. But first, we need to access the property to delete it. The Object property can be accessed either using the dot property accessor or the square brackets property accessor.

  Deleting using the Dot Way

  Let us create an employee object called emp that will be used for further operations.

  Let us delete the age property using the dot way.

  Explanation:

  In the above-given output, we can see that the property age of the object emp has been deleted successfully using the delete operator(dot way).

  Deleting using the Square Brackets Way

  Let us delete the designation property of the same object emp using the square brackets way.

  Explanation:

  In the above-given output, we can see that the property designation of the object emp has been deleted successfully using the delete operator(square brackets way).

  2. Remove a Property from a JavaScript Object using Object Destructuring

  Object Destructuring can also be used for removing a property from an object, but there’s a catch, Object Destructuring does not mutate(or change) the original object, instead creates a new object which does not consist of the deleted property. This way the original object remains intact(does not change).

  Explanation:

  In the above-given example, we used object destructuring to remove a property from an object. When we used object destructuring on the original object laptop to remove the property model from it, we got the new object myLaptop without that property. Again, we can see in the output that the original object did not change.

  3. Remove a Property from a JavaScript Object using the Reflect.deleteProperty() method

  The Reflect.deleteProperty() method is provided by one of the built-in JavaScript objects called ‘Reflect’. This method is like the function form of the delete operator that we already discussed.

  Explanation:

  In the above-given example, we had an object called ‘cars’ with three properties. We used the Reflect.deleteProperty() method to delete the car2 property from that object. The output proves that the car2 property has been successfully deleted from the cars object.

  At last, I would like to add that it does not matter whether you use the delete operator or Reflect.deleteProperty() method as both of them do the task in almost same time compexity. But using Object Destructuring consumes more time comparatively. Hence, the delete operator is the most preferred way of removing key from javascript object due to its short syntax and less time complexity.

  Conclusion

  • JavaScript Objects consist of properties that are just the combination of keys and values.
  • Removing a key automatically removes the value associated with that key.
  • There are three ways to remove key from object in JavaScript.
  • We can remove a Property from a JavaScript Object using the delete Operator, Object Destructuring, and Reflect.deleteProperty() method.
  • The delete operator and the Reflect.deleteProperty() method deletes the specified property from the original object.
  • This means that the delete operator and the Reflect.deleteProperty() mutates the original object.
  • The Object Destructuring does not mutate the original object instead it creates a new object which does not contain the deleted property.

  Источник