Why isn’t [1,2,3] equal to itself in Javascript? [duplicate]

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Ok, so first you need to understand how javascript treats values in your program. All of your variables that you create are going to merely be references to a location in memory where that object is stored. Therefore, when you do this:

alert( [1,2,3] == [1,2,3] );

…it does three things:

  1. Place an array ([1,2,3]) onto the heap
  2. Place another array ([1,2,3]) onto the heap (notice it will have a different memory location)
  3. Compare the two references. They point to different objects in different locations in memory, thus it is considered not equal.

You can check for some sane behavior by running this code:

var a = [1,2,3];
var b = a;
alert (a == b)   // Result is true. Both point to the same object.

Now for your question about the string

When you use the == operator tries to convert the two operands to the same type (evil behavior…I know…)

When it does this, it decides to convert both to a string before it does the compare (thus the result is really "1,2,3" === "1,2,3", which evaluates to true.

I can’t give you a complete picture, as there are few people who understand every nuance of the madness that is JavaScript, but hopefully this clears some of the fog.

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