The difference between == and === in js

== and === operators are used to compare JavaScript values ​​for equality. == automatically converts data types, allowing comparison of values ​​of different types. === performs a strict equality comparison, returning true only if both values ​​and data types are the same. NaN is equal to itself only in == comparisons, not in === comparisons. null and undefined are equal only in == comparisons. Depending on these differences, == or === should be used as appropriate.

The difference between == and === in JavaScript

In JavaScript, == and === is an operator used to compare two values ​​for equality. The main difference between them is the way data types are handled.

1. Data type conversion

== operator automatically converts data types before comparing values, allowing values ​​of different types to be compared. For example:

<code class="js">1 == '1' // true</code>

2. Strict equality

=== operator performs strict equality comparison, that is, comparing the value itself and the data type. Returns true if the two values ​​are both equal and of the same type, false otherwise. For example:

<code class="js">1 === '1' // false</code>

3. NaN comparison

NaN (not a number) is a special JavaScript value that represents a non-number that cannot be represented as a number. When comparing using ==, NaN is equal to itself:

<code class="js">NaN == NaN // true</code>

And when comparing using ===, NaN is not equal to itself:

<code class="js">NaN === NaN // false</code>

4. Null and Undefined

In JavaScript, null and undefined are both falsy values. When compared using ==, they are equal:

<code class="js">null == undefined // true</code>

However, when compared using ===, they are not equal:

<code class="js">null === undefined // false</code>

Summary

Based on these differences, the choice between using == or === depends on your comparison needs. If you need automatic type conversion or treating NaN as equal, you can use ==. If you need strict comparison, including values ​​and data types, you should use ===.

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