Detailed explanations and examples of Boolean values, relational operators, and logical operators in JS

We know that Boolean values ​​are true and false. The output of Boolean value operations is: true; false; boolean; boolean. Boolean values ​​can also be used directly without quotation marks.

<script type="text/javascript">
    var a=true;
    var b=false;
    console.log(a);
    console.log(b);
    console.log(typeof a);
    console.log(typeof b);
</script>

RelationshipOperator
＞Greater than sign
＜Less than sign
＞=Greater than or equal to
＜=Less than or equal to
==Equal to
===All equal to
!=Not equal to
!==Not equal to

The results obtained by relational operators are all Boolean values, either true or false

<script type="text/javascript">
    console.log(-6<=9); //true
    console.log(55>9); //true
    console.log(5>=9); //false
    console.log(100<5); //false
</script>

Use ==:

console.log(5==5); //true
console.log(5==6); //false

can be used to determine whether the user is qualified

<script type="text/javascript">
    //得到用户成绩
    var score="parseInt(prompt("请输入成绩"))；
    //输出结果
    alert(score>=60);
</script>

Note that in JS, the = symbol has only one meaning, which means assignment. If If you want to determine whether two things are equal, you need to use the == symbol. You cannot use an equal sign to express an equal relationship.

==This symbol can also be used to verify whether the strings are the same:

console.log("LALALALALA"=="LALALALA Lala");

==This symbol is not rigorous and will convert different types of things into the same type for comparison:

console.log("5"==5); //true
console.log(56="56"); //true

===all equal to

console.log("12"===12); //false
console.log(12==="12"); //false
console.log("55"==="55"); //true
console.log(55===55); //true

In other words, ==two equal signs are not rigorous, "5" and 5 are true; ===three equal signs are more rigorous, "5" and 5 are false.

!= is the opposite of ==; !== is the opposite of ===

console.log(3!=8); //true
console.log(3!="3"); //false
console.log(3!=="3"); //true

Logical operators namely &&: and (and); ||: or ; !: Non
participants in logical operations are all Boolean values. Only true and false can participate in logical operations, and the answer obtained is still a Boolean value.

<script type="text/javascript">
//&&表示“且”，都真才真
console.log(true&&true); //true
console.log(true&&false); //false
console.log(false&&true); //false
console.log(false&&false); //false
</script>

<script type="text/javascript">
    //||表示或者
    console.log(true||true); //true
    console.log(true||false); //true
    console.log(false||true); //true
    console.log(false||false); //false
</script>

! Indicates "non"

console.log(!true); //false
console.log(!false); //true

How to write consecutive ratios
For example, if you want to see if the number 1 is Between 3 and 5,
Wrong way of writing: console.log(3<1<5);
Because the computer will calculate 3<1 first, and the answer will be false, and then false<5, false will Is implicitly converted to 0, 0 < 15 is true.
The correct way of writing should be split and connected with an && in the middle, that is, "3 is less than 1" and "1 is less than 5".

console.log(3<1&&1<5);

The answer obtained is false.

Example: The Traffic Law stipulates that 18-70 years old can take a driver's license test. To determine whether a person can take a driver's license test, then:

//得到用户年龄
var age=parseInt(prompt("请输入年龄"));
//显示结果
alert(age>=18&&age<=70);

I believe after reading these cases You have mastered the method. For more exciting information, please pay attention to other related articles on the php Chinese website!

Related reading:

What does the JS engine look like when it is running?

The server actively sends data back to the client in H5 Implementation steps

How to use the jssplice() method in JS development

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