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📔 today’s small knowledge — JavaScript logic interrupt (2)
JS logic interrupt (1)
Logic interrupts or short circuits
1. The logic is interrupted or
- If the result of expression 1 is true, expression 1 is returned
- If expression 1 results in false, expression 2 is returned
For example 1
console.log(387 || 618)
According to the rules of the above characteristics, 387 | | 618 results should be 387, run it to see how the results, not surprisingly, the console print is 387
387, as expected, returns expression 1 if expression 1 is true
For example 2
Copy the above expression and add another expression to see what happens. It’s still 387 without any accidents
console.log(387 || 618 || 123 + 456 || 110)
If expression 1 is true, then expression 1 is returned, so no matter how many expressions follow, they are interrupted and will not be executed
For example, 3
What if the example expression 1 above is zero??
console.log(0 || 618 || 123 + 456 || 110)
Copy the code
Expression 0 | | the returned result is 618, 618 (1 the result is false, if the expression is returned expression (2), then 618 | | 123 + 456 | | 110618 is for real, it returns expression 1, so the final result is 618
For example 4
So let’s look at another example, like this:
var num = 0
console.log(123 || num++)
console.log(num)
Copy the code
Analysis: by “1 results if the expression is true, it returns 1 expression”, then the code. The console log (123 | | num++) must be the result is 0, then for what the output of num? Is it 1 or 0??
On the console, we can see that the printed result is 0, because the logic is broken, the following is not executed, so num does not increment, the original value is 0
So does it matter if logic breaks heavily?? Obviously, logical interruption is a very important knowledge point, learning JS must master, this in a lot of front-end interviews will often test, so you learned it?
2. To summarize
As described in the previous article, the rules within the logic interrupt and budget are characterized by
- If the value of the first expression is true, expression 2 is returned
- If the value of the first expression is false, expression 1 is returned
The rule characteristic of or operation is
- If the result of expression 1 is true, expression 1 is returned
- If expression 1 results in false, expression 2 is returned
As can be seen from the above, logical interrupts are the opposite of and or. If the value of the first expression is true, it returns expression 2 in the and operation and expression 1 in the or operation
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