Let's say I have the following variables:

var num1 = 48;
var num2 = 420;
var num3 = 39;

And I want to know the max value, for that I use:

var max = Math.max(num1, num2, num3);

Is there a way to know that num2 was the max number? This example only has 3 variables, but let's say I have 20 or 500. I need to know the max value and its variable name in the most efficient way.

Let's say I have the following variables:

var num1 = 48;
var num2 = 420;
var num3 = 39;

And I want to know the max value, for that I use:

var max = Math.max(num1, num2, num3);

Is there a way to know that num2 was the max number? This example only has 3 variables, but let's say I have 20 or 500. I need to know the max value and its variable name in the most efficient way.

• javascript

Share Improve this question Follow asked Jun 9, 2021 at 8:15 CheknovCheknov 2,10277 gold badges3232 silver badges7676 bronze badges 10

• 2 What if you have 2 different variables with the same maximum value? – phuzi Commented Jun 9, 2021 at 8:19
• 4 This sound like an XY problem. What are you trying to do, there may be a better way to achieve your desired result. – phuzi Commented Jun 9, 2021 at 8:20
• 1 Having 500 variables maximum? how do you created? – User863 Commented Jun 9, 2021 at 8:21
• @User863 No maximum, N variables. – Cheknov Commented Jun 9, 2021 at 8:22
• @phuzi In that case it doesn't matter, just I want to get the max number and the name of the variable containing that max number. If there are multiple variables with the same maximum value just the first one maybe? – Cheknov Commented Jun 9, 2021 at 8:23

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7 Answers 7

Sorted by: Reset to default 10

You cannot know the variable name because the variable name is not passed into javascript functions, only the values, but you can have a workaround

with arrays:

var numbers = [48,420,39];

const index = numbers.indexOf(Math.max(...numbers))

console.log(`The max value is the ${index+1}nth value in the array`)

with objects

var num1 = 48;
var num2 = 420;
var num3 = 39;

var numbers = {num1, num2, num3}

const maxVal = Math.max(...Object.values(numbers))
const key = Object.keys(numbers).find(key => numbers[key] === maxVal)

console.log(key, maxVal)

Since you are using var, it will get binded to the window object. Then you can iterate over window object, and get the name of variable. Also, if you follow same naming convention, like num1, num2 etc, you can use a if condition to check if num is present in key or not.

var num1 = 48;
var num2 = 420;
var num3 = 39;

var max = Math.max(num1, num2, num3);

let s = Object.keys(window).filter(key => {
      if (key.includes("num")) {
          return window[key] == max
        }
      });

console.log(s)

An alternative solution using reduce

function getHighestNumber(nums) {
  return nums.reduce((acc, num, index) => {
    if(num > acc.value) {
      acc.value = num;
      acc.index = index;
    }
    
    return acc;
  }, {value: null, index: null});
}

let nums = [48,420,39];
const max = getHighestNumber(nums);

console.log(max);

O(n) Solution

function getMaxIndex(nums) {
  let max = -Infinity, maxIndex = -1;
  
  for (let i = 0; i < nums.length; i++) {
    if (nums[i] > max) {
      max = nums[i]
      maxIndex = i
    }
  }
  return maxIndex
}

const nums = [48, 420, 39]
let i = getMaxIndex(nums)
console.log(i) // 1, because the index of 420 is 1

I would suggest putting the values into an array / list, so that you can pare easily in a for loop. Example:

let nums = [48,420,39]; 
let max = Math.max(nums[0], nums[1], nums[2]);
for(let i = 0; i < 3; i++){
    if(nums[i] == max){
        console.log("The largest is num" + i)
    }
}

this is the best i could think of.

create an array that will hold the variable name and its value like this:

let varAndVal = 
[
  {"varName":"num1",
   "value": 50},
   {"varName":"num2",
   "value": 51},
   {"varName":"num3",
   "value": 52},
]

then I would run over the array and find the max value and its name like this:

 function getMaxNumAndVarName(arr) {
    let i;
   
    // Initialize maximum element
    let maxVar = arr[0];

    // Traverse array elements 
    // from second and pare
    // every element with current max 
    for (i = 1; i < arr.length; i++) {
        if (arr[i].value > maxVar.value)
            maxVar = arr[i];
    }
     
  return maxVar;
}

let varAndVal = [{
    "varName": "num1",
    "value": 50
  },
  {
    "varName": "num2",
    "value": 51
  },
  {
    "varName": "num3",
    "value": 52
  },
]

function getMaxNumAndVarName(arr) {
  let i;

  // Initialize maximum element
  let maxVar = arr[0];

  // Traverse array elements 
  // from second and pare
  // every element with current max 
  for (i = 1; i < arr.length; i++) {
    if (arr[i].value > maxVar.value)
      maxVar = arr[i];
  }

  return maxVar;
}

console.log(getMaxNumAndVarName(varAndVal));

Your variables can be properties of an object, members of a function scope or reside in a module.

1. If they are properties of an object including the global/window object you can access them with Object.keys() and .reduce() to determine the variable with maximum value.

   var object = { var1: 1
                , var2: 2
                , var3: 3
                },
       maxVar = Object.keys(object).reduce((p,c) => object[p] > object[c] ? p : c);
   
   console.log(maxVar); // "var3";
   

   Or use a for in loop.

2. However if you need to define your variables in a function scope then you best make your function a constructor and claim your variable names like this.var1 ... this.varN etc in order to access the scope variables from the instantiated object and repeat 1.

3. Put your variables in a module and do like

   export let name1 = …, name2 = …, …, nameN; // also var, const`
   

   to be imported in your code like

   import * as object from "./myModule";
   

   and repeat 1.