Four different property detection methods in JavaScript comparison

Tag: span indicates false differentiate BLE method inherit ASC log

Four different property detection methods in JavaScript are compared to 1. Using the In method

var o = {x:1}; inch // true inch // false inch // true, the inherited property can be detected inch // true, non-enumerable properties can be detected

2. hasOwnProperty () method

var o = {x:1};o.hasownproperty (//true//false//  False, cannot detect inherited properties //True, non-enumerable properties can be detected

3. propertyIsEnumerable () method

var o = object.create ({y:2= 1; o.propertyisenumerable (///True,x is an enumerable property // False, inherited property, non-enumerable // false, non-enumerable properties cannot be detected

4.!== undefined method

var o = {x:1///True,o has attribute x//True, inherited property can also be detected

One of the weaknesses of this approach is that there is no way to differentiate between nonexistent attributes and values that are undefined, such as:

var o =//falsein//true

Note that this is "!==" instead of "! =" because "!==" can differentiate between undefined and null.
But sometimes it is not necessary to distinguish between "null" and "undefined", as long as you decide that a property is not null or undefined.

// If o contains an attribute x, and the value of x is not undefined or null,o.x multiplied by 2 if null) o.x *= 2;

An inherited property is not enumerable, so it is possible to detect an inherited property, and it must also detect a non-enumerable property.
X indicates that it cannot be detected, √ indicates that it can detect

Detection Method	non-enumerable properties?	inherit property?
Inch	√	√
hasOwnProperty	√	X
propertyIsEnumerable	X	X
!==	√	√

Four different property detection methods in JavaScript comparison