However bash I cheque if an entity has a circumstantial place successful JavaScript?

See:

x = {'key': 1};if ( x.hasOwnProperty('key') ) { //Do this}

Is location different manner to bash it?

2022 Replace

`Object.hasOwn()`

Object.hasOwn() is advisable complete Object.hasOwnProperty() due to the fact that it plant for objects created utilizing Object.create(null) and with objects that person overridden the inherited hasOwnProperty() technique. Piece it is imaginable to workaround these issues by calling Object.prototype.hasOwnProperty() connected an outer entity, Object.hasOwn() is much intuitive.

Illustration

const object1 = { prop: 'exists'};console.log(Object.hasOwn(object1, 'prop'));// expected output: true

First reply

I'm truly confused by the solutions that person been fixed - about of them are conscionable outright incorrect. Of class you tin person entity properties that person undefined, null, oregon mendacious values. Truthful merely decreasing the place cheque to typeof this[property] oregon, equal worse, x.key volition springiness you wholly deceptive outcomes.

It relies upon connected what you're wanting for. If you privation to cognize if an entity bodily accommodates a place (and it is not coming from location ahead connected the prototype concatenation) past object.hasOwnProperty is the manner to spell. Each contemporary browsers activity it. (It was lacking successful older variations of Safari - 2.Zero.1 and older - however these variations of the browser are seldom utilized immoderate much.)

If what you're wanting for is if an entity has a place connected it that is iterable (once you iterate complete the properties of the entity, it volition look) past doing: prop in object volition springiness you your desired consequence.

Since utilizing hasOwnProperty is most likely what you privation, and contemplating that you whitethorn privation a fallback technique, I immediate to you the pursuing resolution:

var obj = { a: undefined, b: null, c: false};// a, b, c all foundfor ( var prop in obj ) { document.writeln( "Object1: " + prop );}function Class(){ this.a = undefined; this.b = null; this.c = false;}Class.prototype = { a: undefined, b: true, c: true, d: true, e: true};var obj2 = new Class();// a, b, c, d, e foundfor ( var prop in obj2 ) { document.writeln( "Object2: " + prop );}function hasOwnProperty(obj, prop) { var proto = obj.__proto__ || obj.constructor.prototype; return (prop in obj) && (!(prop in proto) || proto[prop] !== obj[prop]);}if ( Object.prototype.hasOwnProperty ) { var hasOwnProperty = function(obj, prop) { return obj.hasOwnProperty(prop); }}// a, b, c found in modern browsers// b, c found in Safari 2.0.1 and olderfor ( var prop in obj2 ) { if ( hasOwnProperty(obj2, prop) ) { document.writeln( "Object2 w/ hasOwn: " + prop ); }}

The supra is a running, transverse-browser, resolution to hasOwnProperty(), with 1 caveat: It is incapable to separate betwixt circumstances wherever an an identical place is connected the prototype and connected the case - it conscionable assumes that it's coming from the prototype. You might displacement it to beryllium much lenient oregon strict, based mostly upon your occupation, however astatine the precise slightest this ought to beryllium much adjuvant.

With Underscore.js oregon (equal amended) Lodash:

_.has(x, 'key');

Which calls Object.prototype.hasOwnProperty, however (a) is shorter to kind, and (b) makes use of "a harmless mention to hasOwnProperty" (i.e. it plant equal if hasOwnProperty is overwritten).

Successful peculiar, Lodash defines _.has arsenic:

function has(object, key) { return object ? hasOwnProperty.call(object, key) : false;}// hasOwnProperty = Object.prototype.hasOwnProperty

2023 Replace

Arsenic famous successful John Resig's reply, this is present basically constructed-successful with Object.hasOwn. Lodash/underscore stay fallbacks for circumstances wherever Object.hasOwn is not disposable.

Successful JavaScript, figuring out whether or not an entity possesses a circumstantial place is a communal project, particularly once dealing with dynamic information constructions oregon interacting with APIs. Location are respective approaches you tin return, all with its ain nuances and usage circumstances. Selecting the correct methodology relies upon connected components similar whether or not you demand to cheque for inherited properties, if you're running with possibly null oregon undefined objects, oregon if you're afraid astir the place being outlined however having a worth of undefined. This weblog station goals to completely research these strategies, offering you with the cognition to confidently grip place checks successful your JavaScript codification.

However to Confirm if a JavaScript Entity Accommodates a Peculiar Place

JavaScript provides aggregate methods to cheque for the beingness of a place inside an entity. The easiest methodology is utilizing the successful function. The successful function checks if a place exists inside an entity oregon its prototype concatenation. This means it volition instrument actual equal if the place is inherited from a genitor people oregon prototype. Alternatively, you tin usage the hasOwnProperty() methodology, which checks lone for properties straight outlined connected the entity itself, ignoring inherited properties. Knowing the quality is important for avoiding surprising behaviour, particularly once running with analyzable entity hierarchies.

Utilizing the successful Function

The successful function is a simple manner to cheque if a place exists inside an entity, together with these inherited from its prototype concatenation. It returns actual if the place exists, and mendacious other. This function is peculiarly utile once you demand to cognize if a place is accessible astatine each, careless of wherever it's outlined. Nevertheless, support successful head that it doesn’t separate betwixt a place explicitly fit to undefined and a place that doesn’t be astatine each. So, if you particularly demand to cognize if a place is straight outlined connected the entity and not inherited, another strategies are much due.

javascript const myObject = { sanction: "Illustration", worth: undefined }; console.log("sanction" successful myObject); // Output: actual console.log("worth" successful myObject); // Output: actual console.log("toString" successful myObject); // Output: actual (inherited from Entity.prototype) console.log("nonExistent" successful myObject); // Output: mendacious

Leveraging the hasOwnProperty() Methodology

The hasOwnProperty() methodology is a nonstop manner to find if an entity has a place outlined straight connected itself, with out traversing the prototype concatenation. This methodology returns actual if the entity has the specified place arsenic a nonstop place, and mendacious other. It’s peculiarly utile once you privation to guarantee you’re lone dealing with properties that are explicitly outlined connected the entity case, avoiding immoderate inherited behaviour. Wherefore does this codification using random strings grade "hullo satellite"? This is a important discrimination once iterating complete an entity's properties and you lone privation to procedure the entity's ain properties.

javascript const myObject = { sanction: "Illustration", worth: undefined }; console.log(myObject.hasOwnProperty("sanction")); // Output: actual console.log(myObject.hasOwnProperty("worth")); // Output: actual console.log(myObject.hasOwnProperty("toString")); // Output: mendacious (inherited from Entity.prototype) console.log(myObject.hasOwnProperty("nonExistent")); // Output: mendacious

Alternate Approaches to Confirm Place Beingness

Past the successful function and hasOwnProperty() methodology, JavaScript gives another methods for checking if a place exists successful an entity. 1 communal attack is to straight entree the place and cheque if its worth is not undefined. This tin beryllium accomplished utilizing the dot notation (entity.place) oregon bracket notation (entity['place']). Nevertheless, this methodology has a caveat: if the place is explicitly fit to undefined, it tin pb to incorrect outcomes. Different attack entails utilizing Entity.keys() to acquire an array of the entity's ain place names and past checking if the desired place sanction is included successful that array. These alternate strategies supply flexibility and tin beryllium tailor-made to circumstantial usage circumstances.

Methodology	Statement	Checks Inherited Properties?	Handles `undefined` values?
`in` function	Checks if a place exists successful the entity oregon its prototype concatenation.	Sure	Returns `true` equal if the worth is `undefined`
`hasOwnProperty()`	Checks if the entity has the place arsenic a nonstop place.	Nary	Returns `true` equal if the worth is `undefined`
Nonstop Entree (`object.property`)	Accesses the place worth straight.	Sure	Returns `undefined` if the place doesn't be oregon is fit to `undefined`
`Object.keys()`	Returns an array of the entity's ain place names.	Nary	Does not see properties with a worth of `undefined`

Nonstop Place Entree

Straight accessing a place utilizing dot notation (entity.place) oregon bracket notation (entity['place']) is a communal and concise manner to cheque for its beingness. If the place does not be, JavaScript volition instrument undefined. Nevertheless, a captious caveat is that if the place exists however is explicitly fit to undefined, this methodology volition inactive instrument undefined, making it indistinguishable from a non-existent place. This tin pb to disorder if you demand to differentiate betwixt a place that is deliberately fit to undefined and 1 that merely doesn't be. Ever see this possible ambiguity once utilizing nonstop place entree for beingness checks.

javascript const myObject = { sanction: "Illustration", worth: undefined }; console.log(myObject.sanction); // Output: "Illustration" console.log(myObject.worth); // Output: undefined console.log(myObject.nonExistent); // Output: undefined if (myObject.worth === undefined) { console.log("Worth is undefined (oregon doesn't be)"); }

Using Entity.keys()

Entity.keys() is a methodology that returns an array of a fixed entity's ain enumerable place names, iterated successful the aforesaid command that a average loop would. This is peculiarly utile once you demand to iterate complete the properties of an entity and lone privation to woody with the properties straight outlined connected the entity itself. To cheque if a circumstantial place exists, you tin usage Entity.keys() to acquire the array of place names and past usage the contains() methodology to cheque if the desired place sanction is immediate successful the array. Line that this attack does not see inherited properties.

javascript const myObject = { sanction: "Illustration", worth: undefined }; const keys = Entity.keys(myObject); console.log(keys); // Output: ["sanction", "worth"] console.log(keys.contains("sanction")); // Output: actual console.log(keys.contains("worth")); // Output: actual console.log(keys.contains("toString")); // Output: mendacious console.log(keys.contains("nonExistent")); // Output: mendacious

Successful abstract, selecting the correct methodology to cheque if an entity has a circumstantial place successful JavaScript relies upon connected your circumstantial wants. The successful function is appropriate once you demand to cheque for the beingness of a place successful the entity oregon its prototype concatenation. The hasOwnProperty() methodology is perfect once you privation to cheque for the beingness of a place straight connected the entity itself, with out contemplating the prototype concatenation. Nonstop place entree tin beryllium utilized for elemental checks, however beryllium aware of the ambiguity with undefined values. Entity.keys() gives a manner to acquire an array of the entity's ain place names, permitting you to cheque for circumstantial properties successful a much managed mode. By knowing the nuances of all methodology, you tin compose much strong and dependable JavaScript codification. Research the successful function and the hasOwnProperty() methodology additional to deepen your cognition. For much precocious subjects, see speechmaking astir prototype inheritance successful JavaScript.