JS: why [] = =! [] return true?

Let's start with a piece of code

[] == ![]  //true

'' == ![]  //true

1 == ![]  //false

0 == ![]  //true

![] == false //true

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In this algorithm , and [] == ![] What matches is the condition 7, So call [] == ToNumber(false) Compare . stay 9.3 In the festival ,ToNumber(false) be equal to 0, So the comparison becomes [] == 0 .

Here because [] It's the object , The comparison process takes branches 9, In accordance with the ToPrimitive([]) == 0 Compare .ToPrimitive Call by default toString Methodical （ In accordance with the 8.2.8）, therefore ToPrimitice([]) Equal to an empty string .

result ,[] == ![] The comparison of finally fell to ‘’==false On , according to 11.9.3 The definitions in will be based on branches 5 Compare ToNumber(’’)==0 ,ToNumber(’’) In accordance with the 9.3.1 be equal to 0, So the result is true.