Question

What does the following syntax mean:

1 in [1,2,3,5]

I know it doesn’t search for 1 in the array. But what does it do?

I’ve seen it used in loops:

for (var i in testArray)
{

}

But have also seen this used by itself. Does it mean check if the literal is a valid index in the array or object that is the other operand?

Answer 1

literalinobject means: “Get a property literal from object.”

When used in a loop, the engine will try to access all properties of the object.

1 in [1,2,3,4] doesn’t check for an occurence of an element with a value of 1, but it checks whether element 1 (array[1]) exists or not.