The difference between javaScript '==' and '==='

Both html and php have operators. For the comparison operators in JavaScript, the one that may be used more often is "==". Many people may be unfamiliar with "===", so what exactly do they have? What's the difference?

=== means identity, first compares whether the data types of the variables on both sides are equal, and then compares whether the values ​​of the variables on both sides are equal; == means equality, that is, only compares whether the values ​​of the variables on both sides are equal.

Difference:

==, When the value types on both sides are different, type conversion must be performed first and then compared.
==, no type conversion is done, different types must not be equal.

The following are explained separately:

Let’s talk about "===" first, this is relatively simple. The following rules are used to determine whether two values ​​​​are === equal:

1. If the types are different, they are not equal

2. If both are numeric values ​​and they are the same value , then [equal]; (!Exception) is that if at least one of them is NaN, then [not equal]. (To determine whether a value is NaN, you can only use isNaN() to determine)

3. If both are strings and the characters at each position are the same, then they are equal; otherwise, they are not equal.

4. If both values ​​are true or both are false, then they are equal.

5. If two values ​​refer to the same object or function, they are equal; otherwise, they are not equal.

6. If both values ​​are null or both are undefined, they are equal.
Let's talk about "=="
If two value types are different, they may be equal. Perform type conversion and then compare according to the following rules:

a. If one is null and the other is undefined, they are equal.

b. If one is a string and the other is a numerical value, convert the string into a numerical value and then compare.

c. If any value is true, convert it to 1 and compare; if any value is false, convert it to 0 and compare.

d. If one is an object and the other is a numerical value or string, convert the object into a value of the basic type and then compare. The object is converted to the base type using its toString or valueOf method. The js core built-in class will try valueOf before toString;

e, and any other combination will not be equal.

Summary:

In other words, "==" is a comparison between values, and: "===" is not just It is a comparison between values, and also a comparison between types. Generally, when working on a project, we decide which one to use based on different businesses. Most developers are used to "==", which is not rigorous.

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