How do you compare three variables in javascript?

Compare 3 Values in JavaScript #

To compare 3 values, use the logical AND (&&) operator to chain multiple conditions. When using the logical AND (&&) operator, all conditions have to return a truthy value for the if block to run.

Copied!
const value1 = 10;
const value2 = 10;
const value3 = 10;

if (value1 === value2 && value2 === value3) {
  // 👇️ this runs
  console.log('✅ all 3 values are equal');
} else {
  console.log('⛔️ values are NOT equal');
}

In the code example, we used the logical AND (&&) operator to chain two conditions.

When using the logical AND (&&) operator in an if statement, all conditions have to be met for the if block to run.

The logical AND (&&) operator returns the value to the left if it's falsy, otherwise it returns the value to the right.

The falsy values in JavaScript are: false, null, undefined, 0, "" (empty string), NaN (not a number). All other values are truthy.

This means that if the conditions on both sides of the logical AND (&&) operator evaluate to a value other than the aforementioned 6, the if block is run.

If our example we check if the 3 values are equal. Since the conditions on both sides of the operator return true, the if block is run.

First, the condition on the left of the && is evaluated, if it returns a falsy value, the condition on the right-hand side is not evaluated at all and the else block is run.

Let's look at another example.

Copied!
const value1 = 10;
const value2 = 10;
const value3 = 20;

if (value1 === value3 && value2 < value3) {
  console.log('✅ both conditions are true');
} else {
  // 👇️ this runs
  console.log('⛔️ at least 1 condition is false');
}

In this example, the condition on the left-hand side is evaluated.

It checks if 10 === 20, which returns false. The AND (&&) operator short-circuits and returns false, and the else block is run.

Further Reading #

• How to count the words in a String in JavaScript
• How to use shorthand for if/else statement in JavaScript

I have 3 values that I want to compare f, g and h. I have some code to check that they all equal each other and that none of them are null. I've had a look online but could not find anything that seemed to answer my query. Currently I am checking the code in the following way...

if(g == h && g == f && f == h && g != null && f != null && h != null)
{
//do something
}

This is quite long winded and I might be adding more values, so I was just wondering if there is a quicker way to check that none of the values are null and that all the values equal each other?

Thanks in advance for any help.

asked Apr 2, 2012 at 8:46

5

You could shorten that to

if(g === h && g === f && g !== null)
{
//do something
}

For an actual way to compare multiple values (regardless of their number)
(inspired by/ simplified @Rohan Prabhu answer)

function areEqual(){
   var len = arguments.length;
   for (var i = 1; i< len; i++){
      if (arguments[i] === null || arguments[i] !== arguments[i-1])
         return false;
   }
   return true;
}

and call this with

if( areEqual(a,b,c,d,e,f,g,h) )
{
//do something
}

answered Apr 2, 2012 at 8:52

Gabriele PetrioliGabriele Petrioli

185k34 gold badges254 silver badges306 bronze badges

6

What about

(new Set([a,b,c])).size === 1

answered Nov 19, 2020 at 20:18

olidemolidem

1,76118 silver badges40 bronze badges

5

Works for any number of items.

ES5

if ([f, g, h].every(function (v, i, a) {
  return (
    v === a[0] &&
    v !== null
  );
})) {
  // Do something
}

ES2015

if ([f, g, h].every((v, i, a) => 
  v === a[0] &&
  v !== null
)) {
  // Do something
}

answered Sep 25, 2015 at 19:01

JMMJMM

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0

I suggest you write a function where you give an array with all the values you want to compare and then iterate through the array to compare the values which each other:

function compareAllValues(a) {
     for (var i = 0; i < a.length; i++) {
         if (a[i] === null) { return false }
         for (var j = 0; j < i; j++) {
            if (a[j] !== a[i]) { return false }
         }
     }

     return true;
}

that should be it, I think :)

answered Apr 2, 2012 at 8:52

1

Write a simple function:

var checkAllArguments = function() {
    var len = arguments.length;
    var obj;

    if(len == 0) {
        return true;
    } else {
        if(arguments[0] == null) {
            return false;
        } else {
            obj = arguments[0];
        }
    }

    for(var i=1; i

Now, to check multiple arguments, all you have to do is:

if(checkAllArguments(g, h, f)) {
   // Do something
}

answered Apr 2, 2012 at 8:52

Rohan PrabhuRohan Prabhu

6,9665 gold badges36 silver badges66 bronze badges

Create an array of string and check the existance of next value in there

compareAnswers(a1: string, a2: string, a3: string): boolean {
   this.compareAnswerArr.push(a1);
if (this.compareAnswerArr.includes(a2) == false) {
  this.compareAnswerArr.push(a2);
  if (this.compareAnswerArr.includes(a3) == false) {
    return true;
  } else return false;
}
else return false;}

answered Sep 30, 2019 at 17:16

Add a distinct function to Array.prototype:

Array.prototype.distinct = function() {
    var result = [];
    for(var i = 0; i < this.length; i++) {
        if (result.indexOf(this[i]) == -1) {
            result.push(this[i]);
        }
    }
    return result; 
}

Then do:

var myArray = [f, g, h];
if (myArray.indexOf(null) == -1 && myArray.unique().length == 1)
{
    // no nulls and all elements have the same value!
}

answered Dec 7, 2016 at 13:27

KrisKris

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