In what ways can two identical-looking arrays actually be distinct from each other?

Explore this JavaScript snippet:

var st, ary, ary1, ary2;
ary  = [["a","b","c"], ["d","e","f"]]; // 2D array
ary1 = ary[1];
st   = "d,e,f"; ary2 = st.split(',');
st   = typeof(ary1) + " " + ary1.length + " " + ary1 + '\n';  // All in one string 
st  += typeof(ary2) + " " + ary2.length + " " + ary2 + '\n'; 
st  += (ary1[0]==ary2[0])+'\n';
st  += (ary1==ary2);

console.log(st);
.as-console-wrapper { max-height: 100% !important; top: 0; }

Result:
object 3 d,e,f
object 3 d,e,f
true
false

Why Same yet different? Curious minds inquire!

javascriptarrays

Answer №1

The == operator checks if two objects are the same by comparing their references. It does not consider the content of the objects. Even if you deep clone an array to create a new array, the two arrays will still be considered different.

For example:

Person person1 = new Person("1", "Thomas", "Meier");
Person person2 = new Person("1", "Thomas", "Meier");
Person person3 = person1;

System.out.println(person1 == person2);
// Output: false
System.out.println(person1 == person3);
// Output: true

Answer №2

The reason for this behavior is that arrays in JavaScript are compared based on their references. Each time you create an array, it gets assigned a unique reference. So when you try to compare two arrays, JavaScript actually compares their references rather than their actual values.

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