JavaScript运算符的优先级和关联性

Question

In JavaScript

var x = (5 >= 9 >= 0);
console.log(x);
// returns true

What is happening in that statement and what is the reason for that output?

Answer 1

The Operator precedence and Associativity chart explains what is happening. The expression is evaluated in this order:

/* 1 */ x = (5 >= 9) >= 0;
/* 2 */ x = false >= 0;
/* 3 */ x = true;    

Explanation:

1. >= is left associative the operator between 5 and 9 is evaluated first.
2. >= uses abstract comparison which converts boolean to number ie false becomes 0 ( ref ).
3. The end result is true .

Answer 2

The true statement, is understood as different from zero ... Consequently, false is equals zero ...

The statement:

(5>=9>=0)

Turns into

(false >= 0)

Since 5 is lower than 9. Then, if false is equal zero the result is true

EDIT

As explained here ( All falsey values in JavaScript ), zero is among the falsy values in javascript...