运算符

Logical Operators

Operator	Description	Useage
Logical AND (&&)	expr1 && expr2	Returns expr1 if it can be converted to false; otherwise, returns expr2. Thus, when used with Boolean values, && returns true if both operands are true; otherwise, returns false.
Logical OR (`		`)
Logical NOT (!)	!expr	Returns false if its single operand can be converted to true; otherwise, returns true.

Falsy

• null;
• NaN;
• 0;
• empty string ("" or '' or ``);
• undefined.

MDN:运算符优先级