How to pass a spread operator to a functions parameter

Question

Using spread operator I can get the maximum value of two arrays using Math.max(...firstArr, ...secondArr), and get's the right value, I am trying not to add a spread operator MANUALLY, I am trying to add automatically by creating function, I am trying to add or pass a spread operator before the argument. example

var firstArr = [1,2,3,4,5];
var secondArr = [6,7,8,9];

function myFun() {
    for(var i = 0; i <= arguments.length; i++) {
      var resl = Math.max(...arguments[i]);
      document.write("The maximum value is " + resl);
    }
}

myFun(firstArr, secondArr);

It displays two result values:

The first result will be: "The maximum value is 5"

The second result will be: "The maximum value is 9"

It is not comparing two arrays at a time, Please help me. Thanks.

I don't get what you mean by "*I am trying to add automatically by creating function, I am trying to add or pass a spread operator before the argument.*" Notice that spread is syntax, not an operator, and you cannot "add" it arbitrarily. — Bergi, Feb 17 '17 at 02:02
What do you mean by "*It is not comparing two arrays at a time*"? What is the expected result that you would like to get from which call? — Bergi, Feb 17 '17 at 02:03

score 3 · Accepted Answer · answered Feb 17 '17 at 02:11

You seem to be saying that you want your function to take a variable number of separate arrays as arguments, and then find the maximum number within any of those arrays.

If so, you can say [].concat(...arguments) to create a single new array with all of the values from the individual arrays that were arguments, then use the spread operator to pass that new array to Math.max(). (You don't need a loop.)

var firstArr = [1,2,3,4,5];
var secondArr = [6,7,8,9];

function myFun() {
    var resl = Math.max(...[].concat(...arguments));
    console.log("The maximum value is " + resl);
}

myFun(firstArr, secondArr);

Bergi · Answer 2 · 2017-02-17T02:16:53.593

3

It sounds like what you are trying to do is

function myFun(...arrays) {
    const allValues = [].concat(...arrays);
    return Math.max(...allValues);
}
console.log("The maximum value is " + myFun([1,2,3,4,5], [6,7,8,9]));

However I would recommend to avoid spread syntax with potentially large data, and go for

function myFun(...arrays) {
    return Math.max(...arrays.map(arr => Math.max(...arr)));
}

or even better

function myFun(...arrays) {
    return arrays.map(arr => arr.reduce(Math.max)).reduce(Math.max);
}

edited Feb 17 '17 at 02:16

answered Feb 17 '17 at 02:11

Bergi

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Which of your map and reduce options is faster? (It looks to me like the first would have far fewer calls to `Math.max()`, but I'm not sure if that matters.) – nnnnnn Feb 17 '17 at 02:20
@nnnnnn I didn't care so much about speed as about [still working with large arrays](http://stackoverflow.com/q/42263108/1048572) – Bergi Feb 17 '17 at 02:24
@Bergi Thank you so much for your reply it really helps, thanks again ... :) – Rasool Feb 17 '17 at 02:39
Oh. I guess you did say "potentially large data", but it didn't occur to me that that meant "potentially large number of arguments". I can see why the reduce option would help with that, thanks. – nnnnnn Feb 17 '17 at 02:49

score 0 · Answer 3 · answered Feb 17 '17 at 02:16

0

You can use rest element at function declaration, pass an array of arrays each preceded by spread element to function parameters and spread element within function

function myFun(...arr) {
  return Math.max.apply(Math, ...arr)
}

myFun([...firstArr, ...secondArr /*, ...nArr*/ ]);

answered Feb 17 '17 at 02:16

guest271314

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`myFun([firstArr, secondArr, arrN].reduce((a, b) => [...a, ...b]))` – guest271314 Feb 17 '17 at 02:45

How to pass a spread operator to a functions parameter

3 Answers3