javascript - 空数组似乎同时等于true和false(Empty arrays seem to equal true and false at the same time)

Question

Empty arrays are true but they're also equal to false.(空数组为true，但也等于false。)

var arr = []; console.log('Array:', arr); if (arr) console.log("It's true!"); if (arr == false) console.log("It's false!"); if (arr && arr == false) console.log("...what??"); I guess this is due to the implicit conversion operated by the equality operator.(我猜这是由于相等运算符进行隐式转换所致。) Can anyone explain what's going on behind the scenes?(谁能解释幕后发生的事情？)   ask by Patonza translate from so

Answer 1

You're testing different things here.(您在这里测试不同的东西。)

if (arr) called on object (Array is instance of Object in JS) will check if the object is present, and returns true/false.(if (arr)在对象（数组是JS中Object的实例if (arr)调用的if (arr)将检查该对象是否存在，并返回true / false。) When you call if (arr == false) you compare values of this object and the primitive false value.(调用if (arr == false) ，将比较此对象的值和原始false值。) Internally, arr.toString() is called, which returns an empty string "" .(在内部，将调用arr.toString() ，它返回一个空字符串"" 。) This is because toString called on Array returns Array.join() , and empty string is one of falsy values in JavaScript.(这是因为在Array上调用的toString返回Array.join() ，而空字符串是JavaScript中虚假的值之一。)