Turn: JS comparison rules for different types of objects

Type (x)	Type (y)	Result
Type (x) ==type (y)		X===y
otherwise ...		False
Null	Undefined	True
Undefined	Null	True
Number	String	X==tonumber (y)
String	Number	Tonumber (x) ==y
Boolean	(any)	Tonumber (x) ==y
(any)	Boolean	X==tonumber (y)
String or number	Object	X==toprimitive (y)
Object	String or number	Toprimitive (x) ==y

~~~1. Always convert to the same primitive type and make a judgment, 2. Logical values are always converted to numeric types, 3. Numeric types and string type comparisons, always converting strings to numeric values.

Example one:

[0]==ture;

First, the ture will be tonumber, the result is 1, the formula and conversion to [0]==1

Then [0] will be ToString (), the result is "0", the formula is converted to "0" ==1

Then "0" will be Tonumber (), the result is 0, the formula is converted to 0==1

Finally, the formula is converted to 0===1 according to type (x) ==type (y).

So [0]==true will get false

Example two:

"Potato" ==true;

First, True is Tonumber, the result is 1, and the formula translates to "potato" ==1

Then "potato" will be tonumber, the result is Nan, and the formula is converted to Nan==1

According to typeof (X) ==typeof (y), the formula is converted to Nan===1

So the "potato" ==true will get false.

Example three:

Object with GetValue

str = new number (1);

str.tostring = function () {return "2"};

Str==1;

Here typeof str = = "Object", so the STR is toprimitive, this will be valueof to Str is worth 1

So the formula turns into 1==1.

So str==1 get True

Example four:

Object with ToString

var obj = {

Tostring:function () {return "2"}

};

Obj==1

Here typeof obj = = "Object", toprimitive to obj, first valueof get object, continue to ToString () to get "2", the formula is "2" ==1

The Tonumber of "2" is 2, and the formula is converted to 2==1.

So obj==1 get False

Example 5:

[]==[]

The left and right are different objects, so false

! []==[]

First of all! []==false, here [] is an object that exists, if it is forced specifically for the bool type, through!! [] get ture, so! []==false, this time the formula for false==[]

Then false is specifically for 0, which is specifically for 0==[]

Then [] specifically for "", the formula is 0== ""

Then "" to 0, the formula for 0==0

So! []==[] Get True

Example 6:

! {}=={}

First of all! {} is designed to be false, and rules and 5 are converted to false=={}

False for 0, the formula is converted to 0=={}

Toprimitive for {} gets "[Object Object]", which is specifically 0== "[Object Object]"

Tonumber for "[Object Object]" gets NaN, which is specifically for 0==nan

So! {}=={} Get false