Find the Max Value in an array using JavaScript function

Question

I have this function, the purpose is to find the maximum (number) element in an array, the value is coming from an argument. Can you please explain what is going on line by line with the code below.

function max(arr){
 var max = arr[0];
 for(var i=1; i<arr.length; i++){
   if(arr[i] > max){
     max = arr[i];   
   }
  }
return max;
}

max([4,12,3,8,0,22,56]); //output is 56

Answer 1

Before going through the loop, your function accepts the first array element's value as a "starting"(initial) maximum. That value was 4.
On every loop iteration, each array value is compared with initial "maximum".
If the current value is bigger than previous maximum value - that current value overrides it and becomes the maximum.
But ... there is much easier and better way: is to use built-in Javascript objects, like Math.
Consider the following search of max value:

var arr = [4,12,3,80,0,22,56];
var max = Math.max.apply(null, arr);
console.log(max); // 80

The above approach is preferable for searching min/max values.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/max

Answer 2

Line one. max function is passed the array [4,12,3,8,0,22,56],

Line two. max variable is set to the first item in the array. max is 4,

Line three. A for loop is started which will start from 1 and keep looping for the length of the arr array.

Line four. Checks if the current array value is larger than the max value.

So, first time around it checks if arr[1] is greater then max. If yes, max is set to arr[1] First loop checks if (12 > 4) it is so max = 12

Second time around it checks if arr[2] is greater than max. Second loop checks if(3 > 12) it is not so max = 12

Third time around it checks if arr[3] is greater then max. Third loop checks if (8 > 12) it is not so max = 12

Fourth time around it checks if arr[4] is greater then max. Fourth loop checks if (0 > 12) it is not so max = 12

Fifth time around it checks if arr[5] is greater then max. Fifth loop checks if (22 > 12) it is so max = 22

Sixth time around it checks if arr[6] is greater then max. Sixth loop checks if (56 > 22) it is so max = 56

Line eight. The loop has finished and max is returned. max is 56