Differences between two equal signs and three equal signs in js _ basic knowledge

This article introduces the differences between two equal signs and three equal signs in js. For more information, see = equality, = identity Heng.

=, When the value types on both sides are different, type conversion should be performed first and then comparison should be made.

===, No type conversion is required. The types may vary.

The descriptions are as follows:

=, Which is relatively simple. The following rules are used to determine whether two values are equal:

1. If the types are different, [not equal]

2. If both are numerical values and the values are the same, [equal]; (! If at least one of them is NaN, [not equal]. (You can only use isNaN () to determine whether a value is NaN)

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

4. If both values are true or false, [equal].

5. If both values reference the same object or function, [equal]; otherwise [not equal].

6. If both values are null or undefined, [equal].

Then, according to the following rules:

1. If the two values are of the same type, compare them with =.

2. If the two values have different types, they may be equal. Perform type conversion and comparison based on the following rules:

A. If one is null and the other is undefined, [equal].

B. if one is a string and the other is a numerical value, convert the string to a numerical value before comparison.

C. If any value is true