[[]][ []] [ []] 在 JavaScript 中如何產生字串「10」？

How Does ++[[]][+[]]+[+[]] Produce the String "10"?

In JavaScript, the perplexing expression ++[[]][+[]]+[+[]] has the rather unexpected result of returning the string "10." Let's unravel the mystery behind this curious behavior.

1. Deconstructing the Expression:

If we break down the expression step by step, it can be dissected as follows:

++[[]][+[]]
+
[+[]]

2. Interpreting the Subparts:

• +[]: This expression coerces the empty array [] into a number, which evaluates to 0.
• [[]][+[]]: Retrieving the first element of the inner array [], which is the empty array itself.
• ++[[]][+[]]: Increments the number equivalent of our referenced array ([] = 0) by one, resulting in 1.
• +[]: Same as before, transforms the empty array [] into the number 0.

3. Simplification and Concatenation:

Now we can simplify the expression even further:

1
+
0

JavaScript's concatenation rules apply when it encounters the + operator with operands of different types. Since one operand is a number (1) and the other is an array (0), the array is coerced into a string ("0").

4. String Concatenation:

The result of the addition is a string concatenation:

"1" + "0" === "10"

5. Wrapping Up:

Thus, we discover the hidden path through which ++[[]][+[]]+[+[]] skillfully manipulates coercion and concatenation to produce the enigmatic result of "10."

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