Unfamiliar use of square brackets in calling a function

Question

In the middle of this page, I find the code below.

var plus = function(x,y){ return x + y };
var minus = function(x,y){ return x - y };

var operations = {
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Answer 1

It's called bracket notation. In JavaScript you can use it to access object properties.

Answer 2

My JavaScript book says that object properties need be named with arbitrary names. But '+' and '-' are not names. From the original question, it is inferred that object properties just need be keyed, not named.

Answer 3

operations is an object and when you do operations[property] you will get the associated function and then you are passing the operands as x and y.

operations['+'] is function (x,y){ return x + y } which is plus

operations['-'] is function (x,y){ return x - y } which is minus

Answer 4

It is a dictionary access, which is like an array, but with a key instead of a numeric index.

operations['+'] will evaluate to the function plus, which is then called with the arguments plus(x,y).

Answer 5

here operations is an object where the symbols + and - refers to two functions.

operations[operation] will return a reference to function plus where value of operation is + and then the following () will invoke the function