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This article mainly introduces what the exclamation mark means in JavaScript. It has a certain reference value. Interested friends can refer to it. I hope you can learn a lot after reading this article. Let's take a look at it.

In JavaScript, the exclamation point "!" Refers to the logical non-operator, is a Boolean inverse operation, directly before the Operand, syntax "! Operand"; "!" The operator converts the value of the Operand to a Boolean value, which is then reversed and returned.

The operating environment of this tutorial: windows7 system, javascript1.8.5 version, Dell G3 computer.

In JavaScript, the exclamation point "!" Refers to logical non-operators.

Example of an operator name! Logic is not! X means that if x is not true, it is true.

Logic is not arithmetic! Is a Boolean inversion operation (NOT). As a unary operator, it is placed directly before the Operand, converting the value of the Operand to a Boolean value, then inverting it and returning it.

Example 1

The logical non-operation return values of some special operands are listed below.

Console.log (! {}); / / return falseconsole.log (! 0) if the Operand is an object; / / return trueconsole.log (! (n = 5)); / / returns falseconsole.log (!) if the Operand is any number that is not zero. Null); / / if the Operand is null, return trueconsole.log (! NaN); / / if the Operand is NaN, return trueconsole.log (! Infinity); / / return falseconsole.log (! (- Infinity)) if the Operand is Infinity; / / return falseconsole.log (!) if the Operand is-Infinity Undefined); / / return true if the Operand is undefined

Example 2

If you perform two logical non-operational operations on an Operand, it is equivalent to converting the Operand to a Boolean value.

Console.log (! 0); / / return trueconsole.log (! 0); / / return false

Note: the return value of a logical non-operation must be a Boolean value.

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