Table of Contents
1. Arithmetic Operators
2. Relational Operators
3. Logical Operators
4. Priority of Operators
One, arithmetic operators
- The common arithmetic operator
+: is equivalent to the addition operation in mathematics; 222+333=555
-: equivalent to the subtraction operation in mathematics; 666-333=333
: equivalent to the multiplication operation in mathematics; 333 2=666
/: It is equivalent to the division operation in mathematics; 666/333=2
%: it is equivalent to the remainder operation in mathematics; 9%4=1 - When performing arithmetic operations on data of non-number type (string/boolean/undefined/null), it must be implicitly converted (through the Number() function) into a number before calculation
console.log('5' - 3);//5-3=2
console.log('5' * '3');//5*3=15
console.log('30' / '5'); // 30/6=6
console.log(5 - true); //5-1=4
console.log(5 + false ); //5+0=5
console.log(false - true); //0-1=-1
console.log(null + false ); //0+0=0
console.log(null - 2); //0-2=-2
- When NaN (including the data converted to NaN by Number()) is calculated with other data, the result is always equal to NaN (except for the result of addition to a string).
console.log('哈哈' - 5); //NaN Number('哈哈') = NaN
console.log('5a' - 5); //NaN Number('5a') = NaN
console.log(5 - {
}); // NaN Number({}) = NaN
console.log(undefined %'2');//NaN Number(undefined) = NaN
console.log('vbb3.6d' * 2); //NaN Number('vbb3.6d') = NaN
console.log(NaN+2);//NaN
- Special string addition- any data and string addition operation is in the process of spelling
console.log('我是字符串呀'+10)；//'我是字符串呀10'
console.log（'5'+true +6）;//'5true6'
console.log（'5'-true +'6'）;// '5'-true = 4 ,4 和'6'拼串，'46'
console.log（undefined+'2'）;//'undefined2'
console.log（true+(null*2+'5')+undefined）;// null*2 = 0, 'true05undefined'
Two, relational operators
-
Common relational operators
>, <, >=, <=, == (equal to),! = (Not equal to), == = (all equal to), !== (incomplete, etc.); the result of the relational operation is Boolean value -
Relational operations follow the rules
a. Numbers are compared normally;
b. Non-digital types are converted into numbers first and then compared
. c. When comparing strings, the comparison is performed according to the number of digits.
console.log('5' > 3);//true 5>3
console.log('5' != 3);//true 5!=3
console.log(3 != 3);//false
console.log('3' != 3);//false
console.log('3' !== 3);//true
console.log(false > 0);//false 0>0
console.log(true > -1);//true0>-1
console.log(''>-1);//true 0>-1
console.log('5' > '4');//true
console.log('5a' > 3);//true
console.log(' ' > '');//true
console.log(' ' > 0);//false 0>0
console.log('5a' < '5b');//true
console.log('9a' < '3z');//false
d. By default, NaN is not equal to any value, including itself.
e. By default, null and undefined are equal to each other, and also equal to itself; except that they are not equal to any other value.
console.log(undefined > -1);//false
console.log(null > -1);//false
console.log(null == null);//false
console.log(null == 0);//false
console.log(null == false);//false
console.log(null == '');//false
console.log(null == undefined);//true
console.log(undefined == undefined);//true
console.log(undefined == 0);//false
console.log(undefined == false);//false
console.log(undefined == '');//false
console.log(NaN == NaN);//false
f.==It only requires that the values of the two data are equal.
g.===Full equality requires that the size and data type of the two data values are equal.
console.log('5' == 5);//true
console.log(5 == 5);//true
console.log('5' === 5);//false 数据类型不同
console.log('5' === '5');//true
Three, logical operators (short-circuit expression)
1. Summary of the usage of logical operators
&& (and): If there is false, then it is true.
|| (or): If there is truth, it is true, and all false is false
! (Non): Invert operation
2. Practice
console.log(5 > 3 && 5 > 7);//false 有假即假
console.log(5 > 3 && 5 < 7);//true 都真才真
console.log(5 > 3 && 5 < 7 && 3 != 3);//false
console.log(5 > 3 || 5 > 7);//有真即真
console.log(5 < 3 || 5 < 7);//false
console.log(5 > 3 && 5 > 1);//true
console.log(true && true && true);//true
console.log(true && true);//true
console.log(false && false && true);//false
console.log(5 && 3);//3第一个值为真，返回第二个值
console.log(5 && 0);//0
console.log(0 && 5);//0 有假即假
console.log('haha' && -5 && '');// 前两个都是true，返回最后一个，空字符串，看不见
console.log('(*^__^*) 嘻嘻……' && ' ' && '小左同学');//'小左同学'
console.log('5aaa' > 6 && !'yellowgreen' && 0 - 5 * (3 + 1));//false 第一个值为假，有假即假
console.log(6 && !'yellowgreen' && 0 - 5 * (3 + 1));//false 第二个值为false，有假即假
console.log(6 && 'yellowgreen');//yellowgreen
console.log(!3);//false
console.log(6 && 'yellowgreen' && 0 - 5 * (3 + 1));//-20 算数运算的优先级高于逻辑运算，先算出结果-20，前两个值为真，返回第三个值-20
console.log(!(5 < 3) && !5 < 3 && !undefined && null+'5');// null5 前3个都为true，返回拼串
console.log(false || true || true);//true 有真即真
console.log(5 || 3);//5有真即真
console.log(!(5 < 3) || !5 < 3 || !undefined || null+'5');//true第一个值为真，有真即真不管后边
console.log(5 < 3 || !5 < 3 && !undefined || null+'5');//先算&&，结果为true,有真即真
console.log(5 && 3 || '哈哈' && 8);//3
console.log(5 && (3 || '哈哈') && 8);//8
console.log(0 || 5);//5
Fourth, the precedence of operators
- Unary operator (++-!)> Binary operator> Ternary operator
- The priority of binary operators: arithmetic operators (/ *) (+ -)> relational operators (> <>= <=)> logical operators (&& ||)
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