Question

the following expression returns “e”

alert(["a","b","c","d","e"][[1,2],3,4]);

can anybody tell me why? thanks!

Answer 1

All you need to do is break down the expression:

[
    [1,2],
    3,
    4 
]

You are using bracket notation to access a property on the array literal. The syntax requires an expression. The syntax of an expression allows a single expression to contain many expressions when separated by a comma. Each term of the expression is evaluated left to right and the final value is actually the value of the last term. So your example can be replaced with this:

alert(["a","b","c","d","e"][4]);