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Javascript logical operators include: 1. Logical AND operator "&&"; 2. Logical OR operator "||"; 3. Logical NOT operator "!", which will convert data into Boolean values. , and then negated, the result is true or false.
The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer
Logical operators in JavaScript can be used to determine the logical relationship between variables or values. Usually used for Boolean values, it will return a Boolean value true
or false
.
Operator | Description |
---|---|
&& | and |
|| | or |
! | not |
The &&
, ||
operators can use non-Boolean operands, and will return a non-Boolean value.
JavaScript provides a Boolean data type that only accepts the values true
or false
. We can use the Boolean()
function to determine whether the value of an expression (or variable) is true
or false
.
Example:
Execute the following code in the browser, and a pop-up layer showing true
will pop up:
alert(Boolean(7 > 2));
This means that the result of 7 > 2
is true. Of course, 7 is inherently greater than 2. If it is the other way around, 7 > 2
, then the browser will display false.
Logical AND operator&&
, if the first operand is true
, calculate The result is the second operand. If the first operand is false
, the result is false
(except for special values).
Example:
console.log(true && true); // true 操作数为true则结果为第二个操作数 console.log(true && false); // false console.log(true && 10); // 10 console.log(true && (4 > 7)); // false console.log(false && 10); // false 操作数为false则结果为false console.log(false && ""); // false console.log(" " && 0); // 0 console.log(2 && 7); // 7
Expression that will be converted to false:
null
NaN
0
""
, ''
, ``)undefined
Logical OR||
Operator, if the first operand can be converted to true
(not false
), the result is the first operand, otherwise the result is the second operand.
Example:
console.log(true || true); // true 第一个操作数为true则结果为第一个操作数 console.log(true || false); // true console.log(true || 10); // true console.log(true || (4 > 7)); // true console.log(false || 10); // 10 第一个操作数不是true,则结果为第二个操作数 console.log(false || ""); // console.log(false || 0); // 0 console.log(0 || 7); // 7
Logical NOT operator!
Operator, first Convert the data into a Boolean value and then negate it. The result is true
or false
.
Example:
For example, true
is originally a Boolean value, and if it is inverted, false
will be obtained. false
If you negate it, you will get true
:
console.log(!true); // false console.log(!false); // true console.log(!0); // true console.log(!""); // true console.log(![1, 2, 3]); // false
The number 0
can be converted into a Boolean value false
, if you negate the result is true
. ""
The same applies to empty strings. It is first converted to false
and then inverted to get true
. The array [1, 2, 3]
is converted into a Boolean value true
, and its inversion is false
.
For more programming-related knowledge, please visit: Introduction to Programming! !
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