JS Logical operator | | _javascript Tips

So query the introduction of JS:

1. Logic or operator | | ：

When operator | | Of the two operands is a Boolean value that performs a Boolean or operation on both counts.

It first calculates the first operand, and if the value of the expression can be converted to true, it returns the value of the expression on the left. Otherwise, calculate the second shipment.

Even if | | The operator's operand is not a Boolean, and it can still be treated as a Boolean or operation, because it can be converted to a Boolean value regardless of the type of value it returns.

On the other hand, the number of operations for a non-boolean is used | |, which uses the attribute it returns to a value that is not Boolean. This use of this operator is typically to select the first defined and Non-null value in a set of alternative values (that is, the first value that is not converted to false)

Cases:

var Max=max_width | | Preferences.max_width | | 500