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Md Yasin Miah
Md Yasin Miah

Posted on

How many way to find max number in array on Javascript.

#javascript #devops #array #max

1. With for-loop 

const array = [-29, 5, 0, 3, 111, 99, 2, 99];

function maxNumberInArray(arr) {
    let maxNumber = arr[0];
//same way can apply on other loop like(For In, For Of, While)
    for(let i = 0; i < arr.length; i++){
        if(arr[i] > maxNumber){
            maxNumber = arr[i];
        }
    }
    return maxNumber;
}
console.log(maxNumberInArray(array));
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2. With forEach 

let array = [-1, 10, 30, 45, 5, 6, 89, 17];

function maxNumberInArray(arr) {
  let maxNumber = -Infinity;
  arr.forEach(number => { 
         maxNumber =  number > maxNumber ? number :  maxNumber;
               });
  console.log(maxNumber);
}

console.log(maxNumberInArray(array));
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3. Using Math.max function. 

let array = [-1, 10, 30, 45, 5, 6, 89, 17];
console.log(Math.max(...array))
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4. Using reducer 

let array = [-1, 10, 30, 45, 5, 6, 89, 17];
console.log(array.reduce((element,max) => element > max ? element : max, 0));
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Top comments (5)

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peerreynders profile image
peerreynders •

Put differently:

const array = [-1, 10, 30, 45, 5, 6, 89, 17];
// `(previousValue, currentValue, index, array) => nextValue`
// Notice how all data (`currentValue`, `index`, `array`) 
// associated with the array being folded is "bunched up" 
// to the right/end of the parameter list.
const selectMax = (previous, value) => value > previous ? value : previous;
// 1. `initialValue` is optional without it `array[0]` 
//    becomes the `initialValue` and processing starts 
//    at `array[1]`
// 2. Without `initialValue` an empty array will cause:
//    `TypeError: Reduce of empty array with no initial value`
//    So empty arrays have to be handled separately
const maxValue = array.length > 0 ? array.reduce(selectMax) : undefined;
console.log(maxValue);
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Technically using Number.NEGATIVE_INFINITY would be logically improper if the array had no elements,

While I agree that is exactly what happens with Math.max():

console.log(Math.max()); // -Infinity
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Perhaps that is consistent with

console.log(typeof NaN); // "number"
console.log(typeof Number.NEGATIVE_INFINITY); // "number"
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i.e. return a value that is "a number" put invalidates most following numeric operations without forcing the script to stop (throw an error).

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lexlohr profile image
Alex Lohr • • Edited

With recursion (just for completeness):

const maxInArray = (array, index = 0, max = -Infinity) =>
  index === array.length
  ? max
  : maxInArray(
      array,
      index + 1,
      array[index] > max ? array[index] : max
    )
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jamesdenholm profile image
James Denholm • • Edited

Handling negative numbers could be achieved by using Number.NEGATIVE_INFINITY for initialValue (instead of 0), or even just leaving initialValue empty (as reduce() then uses the first element of the array). Technically using Number.NEGATIVE_INFINITY would be logically improper if the array had no elements, but you'd get a TypeError then anyway.

That said, I don't think element and max being around the wrong way is a practical issue; they are by convention (and for code readability should be swapped), but functionally this implementation of callbackFn will still work as the only thing that matters is that the greater of the two args is returned. It's something I'd punt back in a code review, but it'd pass tests, so to speak.

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bwca profile image
Volodymyr Yepishev •

I think what's funny is that with javascript's dynamic typing sometimes it is a good idea to ensure the array you are using is in fact an array of numbers, i.e.

let array = [-1, 10, 30, 45, 5, 6, 89, 17, "Bob"];
console.log(array.reduce((element,max) => element > max ? element : max, 0));
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would produce "Bob" as the max number, which is hilarious :D

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trangchongcheng profile image
cucheng •

Do you think about this way: array.sort()[0]

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