Introduction to the difference between two equal signs and three equal signs in javaScript_Basic knowledge

In a nutshell: == first convert the type and then compare, === first determine the type, if it is not the same type, it will be false directly.
=== means equality, both sides of the comparison must be absolutely the same

alert(0 == ""); // true
alert(0 == false); // true
alert("" == false); // true

alert(0 === ""); // false
alert(0 === false); // false
alert("" === false); // false

Let’s talk about === first. This is relatively simple. The specific comparison rules are as follows:

1. If the types are different, [not equal]
2. If both are numeric values ​​and 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 [equal]; otherwise [not equal].
4. If both values ​​are true, or both are false, then [equal].
5. If both values ​​refer to the same object or function, then [equal]; otherwise [not equal].
6. If both values ​​are null, or both are undefined, then [equal].

As for ==, the specific comparison rules are as follows:

1. If the two value types are the same, perform === comparison. The comparison rules are the same as above
2. If two value types are different, they may be equal. Perform type conversion and comparison according to the following rules:
a. If one is null and the other is undefined, then [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. JS core built-in classes will try valueOf before toString; the exception is Date, which uses toString conversion. Non-js core objects, Ling Shuo (it’s more troublesome, I don’t quite understand it)
e. Any other combination (array array, etc.) is [not equal].