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timoxley | 8 years ago

> which might promote misunderstanding of the behavior

This isn't a misunderstanding, binary logical operators in JS short-circuit like this by design. I believe && and || returned a boolean value in the past, but were explicitly changed to support this behaviour.

discuss

order

arghwhat|8 years ago

Quoting ECMA-262 First Edition (June 1997), Chapter 11, Section 11 (Binary logical operators)[1]:

    The production LogicalANDExpression : LogicalANDExpression && BitwiseORExpression is evaluated as follows:
    
    1. Evaluate LogicalANDExpression. 
    2. Call GetValue(Result(1)).
    3. Call ToBoolean(Result(2)).
    4. If Result(3) is false, return Result(2).
    5. Evaluate BitwiseORExpression.
    6. Call GetValue((Result(5)).
    7. Return Result(6).
That is, the behavior has always been "If the first expression is false-ish, return the first expression, otherwise return the second expression" ("BitwiseORExpression" is a class of expressions that include a lot of things, including equality operators).

JavaScript does not have any operators that is not explicitly listed in a version of ECMA-262. It would be correct to refer to the construct as a "guard", but incorrect to refer to it as a "guard operator". Calling it "guard operator" also does not promote an understanding of the underlying construct.

1: https://www.ecma-international.org/publications/files/ECMA-S...