Скачать или смотреть JavaScript Array and Object addition 🤯

Let's break down each line of JavaScript code and explain the behavior step-by-step:

1. [] + []
In JavaScript, the `+` operator is used for both addition (when dealing with numbers) and concatenation (when dealing with strings). When you use the `+` operator with arrays, JavaScript tries to convert them to strings and then concatenate them.
a) `[]` is an empty array.
b) When JavaScript tries to convert an empty array to a string, it results in an empty string `""`.
So, `[] + []` is equivalent to `"" + ""`, which results in an empty string `""`.

2. [] + {}
Here, we're adding an empty array to an empty object.
a) `[]` is an empty array, which converts to an empty string `""`.
b) `{}` is an empty object, which converts to the string `"[object Object]"`.
When you concatenate `""` (empty string) with `"[object Object]"`, you get `"[object Object]"`.

3. {} + []
This case is a bit more complex because of how JavaScript parses the code.
a) When `{}` is used at the beginning of a statement, JavaScript interprets it as a block of code, not an object literal. Therefore, `{}` is just an empty block of code.
b) After the empty block of code, we have `+ []`. The `+` operator tries to convert the empty array `[]` to a number, which results in `0`.
So, `{} + []` results in `0`.

4. (!+[]+[]+![]).length
This expression involves several steps, so let's break it down:
a) `+[]` converts the empty array `[]` to a number, which is `0`.
b) `!0` is `true` because `0` is a falsy value and `!` (not) operator inverts it.
c) `true` is implicitly converted to the string `"true"` when concatenated with other strings.
So, `!+[]` becomes `"true"`.
Now, the expression looks like this:
("true" + [] + ![])
d) `[]` is converted to an empty string `""`.
e) `![]` is `false` because `[]` (an array) is a truthy value, and `!` (not) operator inverts it to `false`.
f) `false` is implicitly converted to the string `"false"` when concatenated with other strings.
Now, the expression looks like this:
("true" + "" + "false")
Which simplifies to:
"truefalse"
Finally, we check the length of the resulting string:
("truefalse").length
The length of the string `"truefalse"` is `9`

Summary:
1. `[] + []` results in `""` (an empty string).
2. `[] + {}` results in `"[object Object]"`.
3. `{}` + `[]` results in `0`.
4. `(!+[]+[]+![]).length` results in `9`.


These behaviors are due to how JavaScript handles type conversion and the overloaded `+` operator for both addition and string concatenation.

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