How does one make sense of comparing integers with strings and arrays?

Question

How does one make sense of comparing integers with strings and arrays?

I was experimenting with the == operator in Javascript, and the results were intriguing:

0 == "0" // true

and then

0 == [0] // true

BUT:

"0" == [] // false

It's quite perplexing for someone unfamiliar with Javascript like me.

I also observed:

"0" == [0] // true

and this pattern holds for other values as well:

1 == [1] // true
1 == "1" // true
"1" == [1] // true

101 == "101" // true
101 == [101] // true
"101" == [101] // true

It seems to revolve around comparing 0 with an empty array [].

What is the logic behind this behavior?

javascript logic equality

Answer 1

Answer №1

Upon reviewing the Loose equality using == chart on the Mozila Developer Network found here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness, an interesting observation can be made.

For example, when Operand A is a string like "0" and Operand B is an object such as [], Operand B will be converted to a primitive type similar to how new String([]) would return "".

A == ToPrimitive(B)

Exploring further,

> typeof "0"
 "string"
> typeof []
 "object"

> "0"=="" // this will result in false

Another comparison to consider is

> 0==[]  // which will actually return true

Answer 2

Upon reviewing the Loose equality using == chart on the Mozila Developer Network found here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness, an interesting observation can be made.

For example, when Operand A is a string like "0" and Operand B is an object such as [], Operand B will be converted to a primitive type similar to how new String([]) would return "".

A == ToPrimitive(B)

Exploring further,

> typeof "0"
 "string"
> typeof []
 "object"

> "0"=="" // this will result in false

Another comparison to consider is

> 0==[]  // which will actually return true

Answer 3

Answer №2

One reason for this phenomenon is type coercion (using double =). Essentially, when comparing variables of different types, Javascript will attempt to convert them to the same type before making the comparison. To prevent this, it is advisable to use triple equals (===) when comparing variables.

If you want to delve deeper into Javascript, I suggest checking out these recommended books (available online for free!):

https://github.com/getify/You-Dont-Know-JS

However, if you are specifically interested in this topic, you may find this book useful:

https://github.com/getify/You-Dont-Know-JS/blob/master/types%20%26%20grammar/ch4.md

PS. Your specific example is elaborated on in detail towards the end.

Best of luck!

Answer 4

One reason for this phenomenon is type coercion (using double =). Essentially, when comparing variables of different types, Javascript will attempt to convert them to the same type before making the comparison. To prevent this, it is advisable to use triple equals (===) when comparing variables.

If you want to delve deeper into Javascript, I suggest checking out these recommended books (available online for free!):

https://github.com/getify/You-Dont-Know-JS

However, if you are specifically interested in this topic, you may find this book useful:

https://github.com/getify/You-Dont-Know-JS/blob/master/types%20%26%20grammar/ch4.md

PS. Your specific example is elaborated on in detail towards the end.

Best of luck!

Answer 5

Answer №3

Utilizing the Abstract Equality Comparison Algorithm, the process is initiated. Let's delve into a specific example to illustrate how it functions:

0 == [0]

The primary objective of AECA is to unify the types of both the left-hand side and right-hand side. As per the outlined algorithm, recursive steps are executed internally to ensure consistency in types on both sides.

i]   0 == [0]
ii]  0 == toPrimitive([0])
iii] 0 == '0'
iv]  0 == toNumber('0')
v]   0 == 0
vi]  true

Answer 6

Utilizing the Abstract Equality Comparison Algorithm, the process is initiated. Let's delve into a specific example to illustrate how it functions:

0 == [0]

The primary objective of AECA is to unify the types of both the left-hand side and right-hand side. As per the outlined algorithm, recursive steps are executed internally to ensure consistency in types on both sides.

i]   0 == [0]
ii]  0 == toPrimitive([0])
iii] 0 == '0'
iv]  0 == toNumber('0')
v]   0 == 0
vi]  true

Answer 7

Answer №4

In a nutshell, JavaScript typically attempts to convert the sides of an equation to numbers if they are different types. However, for objects, it will invoke the abstract operation toPrimitive (with a hint of default). This operation involves calling .valueOf and then .toString on the result if it remains non-primitive (i.e., not an object).

0 == "0" => 0 == 0 => true

0 == [0] => 0 == "0" ( .valueOf returns [0] so .toString is used)

"0" == [] => "0" == "" => false ( they have the same type so the string must be the same to be true)

0 == [] => 0 == "" => 0 == 0 : true

You can find more information in the following resource:

https://www.ecma-international.org/ecma-262/8.0/#sec-abstract-equality-comparison

Answer 8

In a nutshell, JavaScript typically attempts to convert the sides of an equation to numbers if they are different types. However, for objects, it will invoke the abstract operation toPrimitive (with a hint of default). This operation involves calling .valueOf and then .toString on the result if it remains non-primitive (i.e., not an object).

0 == "0" => 0 == 0 => true

0 == [0] => 0 == "0" ( .valueOf returns [0] so .toString is used)

"0" == [] => "0" == "" => false ( they have the same type so the string must be the same to be true)

0 == [] => 0 == "" => 0 == 0 : true

You can find more information in the following resource:

https://www.ecma-international.org/ecma-262/8.0/#sec-abstract-equality-comparison

How does one make sense of comparing integers with strings and arrays?

Answer №1

Answer №2

Answer №3

Answer №4

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