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.

casablanca · Accepted Answer · 2012-09-10 00:22:59Z

120

Use an anonymous function:

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

answered Sep 10, 2012 at 0:22

casablanca

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1 Comment

mibbit Over a year ago

this initiates the promise rather than saving it for the Promise.all(). How can I set and consume the promise declaratively?

Peter · Accepted Answer · 2012-09-10 00:25:06Z

56

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]

answered Sep 10, 2012 at 0:25

Peter

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4 Comments

Sridhar Sarnobat Over a year ago

This is the solution that solves the wider problem of passing ancilliary parameters to a map-reduce chain, so gets my vote.

Courtney Over a year ago

@Sridhar-Sarnobat is this an example of a closure ?

Sridhar Sarnobat Over a year ago

@Courtney I’ve never fully figured out what a closure is, but I would guess the answer is yes.

Peter Over a year ago

@Courtney every function in JavaScript will close over the scope in which it was defined. In this specific case the inner anonymous function preserves access to the adjustment argument.

Dima Vinogradov · Accepted Answer · 2022-01-18 08:17:53Z

40

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))

edited Jan 18, 2022 at 8:17

answered Mar 28, 2017 at 5:58

Dima Vinogradov

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Comments

gray state is coming · Accepted Answer · 2012-09-10 00:29:40Z

10

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]

answered Sep 10, 2012 at 0:29

gray state is coming

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Comments

ajaykumar · Accepted Answer · 2016-08-04 11:03:18Z

5

Well!! You can easily pass a second parameter to the map function. The following method is widely used to pass this parameter which generally gets hidden during the call:

values.map(function(x , this) {
    return x*x + this.adjustment;
});

var adjustment = 1;
var values = [1,2,3,4]
values.map(function(x , adjustment) {
    return x*x + adjustment;
});

OR

var adjustment = 1;
var squarefunc = function(x , adjustment) {
    return x*x + adjustment;
};
values = [1,2,3,4]
values.map(squarefunc);

answered Aug 4, 2016 at 11:03

ajaykumar

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Comments

leerssej · Accepted Answer · 2018-02-19 18:44:42Z

1

To perform this within a single function, you can add a dash of IIFE to your Curry.

function mapSingleFunc(values, adjustment) {
  return values.map((adjustment => x => (x * x) + adjustment)(adjustment));
};
console.log(mapSingleFunc([1,2,3,4], 2))

In the most abstract sense you are able to tunnel your values in through the calling array. Adding an IIFE allows you to feed the adjustment in each time in the closure.

edited Feb 19, 2018 at 18:44

answered Feb 19, 2018 at 7:50

leerssej

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Comments

MCFreddie777 · Accepted Answer · 2018-12-25 19:32:55Z

1

ES6+ :

values.map( x => squarefuncwithadjustment(x,2) );

answered Dec 25, 2018 at 19:32

MCFreddie777

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Comments

Menzies · Accepted Answer · 2017-07-14 19:23:41Z

-2

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

Then

values = values.map( x => squarefuncwithadjustment(x, 2) );

answered Jul 14, 2017 at 19:23

Menzies

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