Comparison: x == a is true, x == b is true, but a == b is false

Question

I have the following javascript code:

        console.log("Line: 89");
        console.log(products[i]['barcodes'][j]);
        console.log(barcode);
        console.log(barcode == products[i]['barcodes'][j]);
        console.log(barcode == 888);
        console.log(products[i]['barcodes'][j] == 888);
        console.log(888 == 888);

And I'm seeing the following output in the console

Line: 89
888
888
false
true
true
true

How is it remotely possible that barcode == products[i]['barcodes'][j] evaluates to false? How am I supposed to compare these two values?

Answer 1

Consider the following:

var a = '888';
var b = '888    ';
console.log(a); // 888
console.log(b); // 888
console.log(a == b); // false
console.log(a == 888); // true
console.log(b == 888); // true

When you compare a and b, they are both strings - and are compared directly, without any typecast. So whitespace at the end of b does matter here.

However, when you compare both a and b to number 888, the strings stored in these variables are first converted to a number (where the trailing whitespace at the end of '888 ' is ignored) before being compared.

Answer 2

Well, since we don't know what either of those two variables are we can't say. However we can guess that they are not both integers.

From MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comparison_Operators

If the two operands are not of the same type, JavaScript converts the operands, then applies strict comparison. If either operand is a number or a boolean, the operands are converted to numbers if possible; else if either operand is a string, the string operand is converted to a number if possible. If both operands are objects, then JavaScript compares internal references which are equal when operands refer to the same object in memory.

Answer 3

Javascript types can be flaky, and most likely the types are different. You'll have to do something to equalize the types such as

parseInt(barcode) == parseInt(products[i]['barcodes'][j])