Question

49

Empty arrays seem to equal true and false at the same time

rated 0 times [ 56] [ 7] / answers: 1 / hits: 80760 / 13 Years ago, wed, march 30, 2011, 12:00:00

Empty arrays are true but they're also equal to 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.

Can anyone explain what's going on behind the scenes?

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kenyonc

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3 Years ago

answered 13 Years ago ravenl · Accepted Answer

You're testing different things here.

if (arr) called on object (Array is instance of Object in JS) will check if the object is present, and returns true/false.

When you call if (arr == false) you compare values of this object and the primitive false value. Internally, arr.toString() is called, which returns an empty string .

This is because toString called on Array returns Array.join(), and empty string is one of falsy values in JavaScript.