Question

Look at the 3 lines of code within this Javascript function. Assume that y will always be a String:

function example(x, y) {
    var s = {};
    s[y]  = x;
    return s;
}

Bearing in mind the following:

1. Without wrapping it further within a function
2. Without using ;

Is it possible to condense the 3 lines of code into one?

Answer 1

Yes, with a little ugly code:

function example(x, y, s) {
  return (s = {})[y] = x, s;
}

The extra parameter s is not passed into the function, it’s only there to be declared as a variable, so you don’t need the extra line var s;. (If you don’t declare it locally it becomes a global variable, which is bad practice.)

The value of the assignment s = {} is what’s assigned, so you can make the assignment and then continue using the value in the expression.

The comma operator returns the last value, e.g. (1,2) returns the value 2. That way you can add , s to the expression to make it return s.

Edit:

Another variation is using s as a variable in a for loop, and exit out of the loop:

function example(x, y) {
  for(var s = {}; s[y] = x, true;) return s;
}