In chrome 87, the length in array gives following output:
length in ['test']
false
but if we try with more elements, it outputs following:
length in ['test', 'test2']
true
Can somebody explain these different outputs?
2 Answers
The length you're using refers not to the 'length' property, but the value contained in the global identifier length, which exists on window. window.length is, per MDN:
Returns the number of frames (either
<frame>or<iframe>elements) in the window.
So, your code will produce that result if you have exactly 1 frame or iframe in the window - since the second array has a [1] property, but the first array does not have a [1] property.
Live snippet illustrating this:
// NOTE THE EXISTENCE OF ONE IFRAME in the HTML
console.log(length in ['test']);
console.log(length in ['test', 'test2']);<iframe></iframe>Similarly:
const length = 3;
console.log(
length in [0, 1, 2, 3, 4, 5] // true; more than 3 items
);
console.log(
length in [0, 1] // false; less than 3 items
);
answered Dec 15, 2020 at 4:45
CertainPerformance
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Comments
length in your snippets is a variable, which I assume is defined somewhere else and has some value. Depending on its value length in [0, 1] can return true or false.
Since you mentioned Chrome, I assume you're running this snippet in chrome dev tools. In this case length is a global variable (actually, it's a property of window: window.length). Check its value - it's probably 1. This explains why 1 in ['test'] is false (there is no element with index 1 here), but 1 in ['test1', 'test2'] is `true.
If you want to check a presence of a property "length", you need to have it as a string:
'length' in []
In this case it will return true for any array - because all arrays have the "length" property
length?