What makes a single numerical value in an array suitable for basic arithmetic operations?

Question

What makes a single numerical value in an array suitable for basic arithmetic operations?

I find it puzzling how an empty array or an array with just one "numerical" value can be used in various calculations.

[] * [] === 0 // true

[2] * [2] === 4 // true

["2"] * ["2"] === 4 // true

Interestingly, not every operator behaves in the same way.

[2] + [1] === 3 // false, actual result is "21"

[2] - [1] === 1 // true

I decided to experiment with other comparisons, and here's what I found:

[4] === "4" // false
[4] === 4 // false

Normally, one would expect NaN in such arithmetic operations. I wonder if JavaScript's array behavior is due to some internal utilization of the toString method?

javascript arrays

Answer 1

Answer №1

Arrays in JavaScript can be coerced into strings, resulting in comparisons like [] == "", [1] == "1", and [1, 2] == "1,2".

When performing certain mathematical operations on strings, they are automatically converted to Number types.

For instance, the expression [2] * [2] is transformed into "2" * "2", which eventually becomes 2 * 2. It's even possible to mix data types, such as [2] * 2 or "2" * [2].

Using the + operator concatenates strings instead of converting them to numbers. This explains why "2" + "2", "2" + [2], and [2] + [2] all result in "22".

Answer 2

Arrays in JavaScript can be coerced into strings, resulting in comparisons like [] == "", [1] == "1", and [1, 2] == "1,2".

When performing certain mathematical operations on strings, they are automatically converted to Number types.

For instance, the expression [2] * [2] is transformed into "2" * "2", which eventually becomes 2 * 2. It's even possible to mix data types, such as [2] * 2 or "2" * [2].

Using the + operator concatenates strings instead of converting them to numbers. This explains why "2" + "2", "2" + [2], and [2] + [2] all result in "22".

Answer 3

Answer №2

Facing the traditional issue of using + for string concatenation.

In the realm of Javascript, an array is considered an Object. When attempting to convert objects into primitive values, a specific order must be followed:

<obj>.toString()
<obj>.toNumber()
<obj>.toBoolean()

When the * operator is utilized, converting to a string is not feasible, resulting in a fallback to toNumber().

However, with the + operator, the initial conversion method is toString(). As the + operator also serves as the string concatenation operator, the expression is then evaluated as an array.

Indeed, dealing with javascript can lead to some complex scenarios.

Edit:

For more in-depth information, refer to this resource.

Answer 4

Facing the traditional issue of using + for string concatenation.

In the realm of Javascript, an array is considered an Object. When attempting to convert objects into primitive values, a specific order must be followed:

<obj>.toString()
<obj>.toNumber()
<obj>.toBoolean()

When the * operator is utilized, converting to a string is not feasible, resulting in a fallback to toNumber().

However, with the + operator, the initial conversion method is toString(). As the + operator also serves as the string concatenation operator, the expression is then evaluated as an array.

Indeed, dealing with javascript can lead to some complex scenarios.

Edit:

For more in-depth information, refer to this resource.

Answer 5

Answer №3

When it comes to the + operator, it acts as a coercive operator on Strings, regardless of whether it is the lvalue or rvalue. The specification states:

If Type(lprim) is String or Type(rprim) is String, then Return the String that is the result of concatenating ToString(lprim) followed by ToString(rprim)

On the other hand, Multiplication follows different rules, as it applies ToNumber conversion. This involves casting a [Number] to -> Number (similar to what + does, but in a later step).

Your final point is addressed by the SameValue algorithm outlined in the specification. It states that if two values are of different types, it returns false, whereas if two objects reference the same pointer, it returns true. Therefore,

a = [1];
b = [1];
a === b; // false

Answer 6

When it comes to the + operator, it acts as a coercive operator on Strings, regardless of whether it is the lvalue or rvalue. The specification states:

If Type(lprim) is String or Type(rprim) is String, then Return the String that is the result of concatenating ToString(lprim) followed by ToString(rprim)

On the other hand, Multiplication follows different rules, as it applies ToNumber conversion. This involves casting a [Number] to -> Number (similar to what + does, but in a later step).

Your final point is addressed by the SameValue algorithm outlined in the specification. It states that if two values are of different types, it returns false, whereas if two objects reference the same pointer, it returns true. Therefore,

a = [1];
b = [1];
a === b; // false

Answer 7

Answer №4

Performing mathematical operations on arrays in JavaScript can result in unexpected behavior. Arrays are converted to strings before the operation is carried out. If you try to multiply arrays, JavaScript will first convert them to numbers:

[] * [] === 0 //  [] -> '' -> 0, resulting in 0 * 0 

[2] * [2] === 4 // [2] -> '2' -> 2, resulting in 4 * 4

["2"] * ["2"] === 4 // ["2"] -> '2' -> 2, resulting in 4 * 4

Strings have a concatenation operator (+) in JavaScript:

[2] + [1] === 3 // '2' + '1', resulting in "21"

However, strings do not have a subtraction operator (-), so JavaScript will convert them to numbers:

[2] - [1] === 1 // true, because they are numbers

The strict equality operator (===) in JavaScript requires objects to have the same type for comparison:

[4] === "4" // false, as you are comparing an array with a string
[4] === 4 // false, as you are comparing an array with a number

Answer 8

Performing mathematical operations on arrays in JavaScript can result in unexpected behavior. Arrays are converted to strings before the operation is carried out. If you try to multiply arrays, JavaScript will first convert them to numbers:

[] * [] === 0 //  [] -> '' -> 0, resulting in 0 * 0 

[2] * [2] === 4 // [2] -> '2' -> 2, resulting in 4 * 4

["2"] * ["2"] === 4 // ["2"] -> '2' -> 2, resulting in 4 * 4

Strings have a concatenation operator (+) in JavaScript:

[2] + [1] === 3 // '2' + '1', resulting in "21"

However, strings do not have a subtraction operator (-), so JavaScript will convert them to numbers:

[2] - [1] === 1 // true, because they are numbers

The strict equality operator (===) in JavaScript requires objects to have the same type for comparison:

[4] === "4" // false, as you are comparing an array with a string
[4] === 4 // false, as you are comparing an array with a number

What makes a single numerical value in an array suitable for basic arithmetic operations?

Answer №1

Answer №2

Edit:

Answer №3

Answer №4

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