How to detect array equality in JavaScript?

Question

There are two arrays in JavaScript, they are both in the following format:

[{'drink':['alcohol', 'soft', 'hot']}, {'fruit':['apple', 'pear']}];

I need to detect if the two arrays are equal or not. they are considered equal if they contain the same elements in a different order. How can I make that?

• Sparky: Would you consider them equal if they contain the same elements in a different order, or do they have to be identical to both content and order? Is case important?
• 6502: Do you mean also checking different ordering recursively? If second array is [{'fruit':['pear', 'apple']}, {'drink':['alcohol', 'hot', 'soft']}] as elements is considered equal to the array you've shown? (note the pear/apple exchange)
• Sparky: Is case important, i.e. should pear and PEAR be considered the same?
• Felix Kling: possible duplicate of how to check javascript array equals?
• Palec: possible duplicate of How to know if two arrays have the same values

Answer 1

1. Check the length of both arrays
2. Loop through the first array, compare each variable to the second array.

If 1 and 2 are both the same, your array is equal.

Function to compare objects/arrays:

Looping through true arrays can be achieved through for(var i=0; i<array.length; i++).
Walking through the properties of such an object can be done by for(var i in object).

function recursiveCompare(obj, reference){
 if(obj === reference) return true;
 if(obj.constructor !== reference.constructor) return false;
 if(obj instanceof Array){
 if(obj.length !== reference.length) return false;
 for(var i=0, len=obj.length; i<len; i++){
 if(typeof obj[i] == "object" && typeof reference[j] == "object"){
 if(!recursiveCompare(obj[i], reference[i])) return false;
 }
 else if(obj[i] !== reference[i]) return false;
 }
 }
 else {
 var objListCounter = 0;
 var refListCounter = 0;
 for(var i in obj){
 objListCounter++;
 if(typeof obj[i] == "object" && typeof reference[i] == "object"){
 if(!recursiveCompare(obj[i], reference[i])) return false;
 }
 else if(obj[i] !== reference[i]) return false;
 }
 for(var i in reference) refListCounter++;
 if(objListCounter !== refListCounter) return false;
 }
 return true; //Every object and array is equal
}

If you don't understand the function, feel free to request an explanation at the comments.

• Rob W: @Sparky Good point. I've reversed the order of the notes. I've also updated my answer, and included a comparison function.
• Sparky: The benefits of being old and programming when languages were a lot slower...<wink>
• Mic: Do you know you can compare arrays in Javascript? And know if they are bigger or smaller.
• Rob W: @Mic What do you mean? Have you actually read the question + answer?
• Mic: @Rob... I think so, did you check my answer below? Something wrong in it?

Answer 2

With Javascript, you can't check if arrays are equals, but you can compare them like this:

var arr1 = ['alcohol', 'soft', 'hot'],
 arr2 = ['apple', 'pear'],
 arr3 = ['soft', 'hot', 'alcohol'];
function isSame(a1, a2){
 return !(a1.sort() > a2.sort() || a1.sort() < a2.sort());
}
console.log( isSame(arr1, arr2) ); //false
console.log( isSame(arr1, arr3) ); //true

The sort put all elements in the same order, and if both < and > comparisons are false it means both are the same.

Answer 3

You can try this JSON.stringify(array1)===JSON.stringify(array2); if you want the order also to be identical in both the arrays.

• Atticus: This will work for you, just keep in mind order does matter here.
• Narendra Yadala: Yes. I was just updating the answer :)
• Atticus: All good :) Wasn't trying to rant on your response, it's a clever way to do it. Just wanted to make sure the OP knew this since he didn't specify

Answer 4

Does this answer your question? How to check if two arrays are equal with JavaScript?

var equal = array1.compareArrays(array2);

• ArchNoob: It gives me "compareArrays" is not a function.
• Zack: This isn't great because compareArrays is not a defined built-in function in Javascript and it's not great practice to much around with the prototype of something as fundamental as the Array class.