Using javascript map with a function that has two arguments

Question

I know that I can use map with a function of one variable in the following manner:

var squarefunc = function(x) {
    return x*x;
};
values = [1,2,3,4]
values.map(squarefunc) // returns [1,4,9,16]

How do I use map with the following function:

var squarefuncwithadjustment = function(x, adjustment) {
    return (x*x + adjustment);
}

where, I want to input value for argument adjustment manually when I call map, say adjustment=2, and have the value of x taken from the array values.

Answer 1

Use an anonymous function:

values.map(
  function(x) { return squarefuncwithadjustment(x, 2); }
);

Answer 2

You could use a callback creation function:

var createSquareFuncWithAdjustment = function(adjustment) {
    return function(x) { return (x * x) + adjustment; };
};

values = [1, 2, 3, 4];
values.map(createSquareFuncWithAdjustment(2)); // returns [3, 6, 11, 18]

Answer 3

As of ES6 you can use:

.map(element => fn(element, params))

In your case if I want to use 3 as adjustment:

values = [1,2,3,4]
values.map(n => squarefuncwithadjustment(n, 3))

Answer 4

If you reverse the order of your arguments, you can bind the adjustment as the first argument, so that the x will be passed as the second.

var squarefuncwithadjustment = function(adjustment, x) {
    return (x*x + adjustment);
}

values.map(squarefuncwithadjustment.bind(null, 2)); // [3, 6, 11, 18]

The first argument to .bind sets the calling context, which doesn't matter here, so I used null. The second argument to .bind binds 2 as the first argument when invoked.

It may be better to store the function as a bound version.

var squareFuncWith2 = squarefuncwithadjustment.bind(null, 2);

Then use it with .map.

values.map(squareFuncWith2); // [3, 6, 11, 18]