undefined === null => false
undefined == null => true
I pondered the logic behind undefined == null and realized only one scenario:
if(document.getElementById() == null) ....
Are there any other reasons why (undefined === null) == false ?
Can you provide other examples of using the strict equality operator === in JavaScript?
What is the reason for (undefined === null) to be evaluated as false?
The reason they are not equal is because of the Strict Equality Comparison Algorithm, which determines them to be false.
Can you provide other examples where the === operator is used in JavaScript?
Using === provides the most reliable outcome. I tend to only resort to using == when I have a specific need for type coercion. (Refer to Abstract Equality Comparison Algorithm for more information.)
null and undefined are distinct concepts. When a variable is defined with var but not initialized, it holds the value of undefined, not null. On the other hand, null signifies that the variable exists and has been set to the specific value null, which is unique in its own right.
The equality operator in JavaScript has its flaws. Crockford observed that it lacks transitivity, prompting him to always recommend using the strict equality operator (===). To illustrate, here's a comparison table from 'Javascript: The Good Parts':
'' == '0' // false
0 == '' // true
0 == '0' // true
false == 'false' // false
false == '0' // true
false == undefined // false
false == null // false
null == undefined // true
=== represents strict equality.
It's important to note that undefined and null have their differences.
== performs type coercion during comparison.
The values of null and undefined can be coerced into each other.
Utilizing type coercion with the == operator may result in outcomes that are not as expected. Upon extensively studying Douglas Crockford's presentations online, particularly on Yahoo video, I have adopted the habit of employing the === operator consistently. With my tendency to default to the strict equality operator, I am now intrigued by the various scenarios in which type coercion is used in JavaScript ;~) these days.
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