Logical Operators:
&&: logical and operator : Summary: it is really only true, false is a fake
|| logical OR operator Summary: are false only false, it is a really true
! Logical NOT operator
! True false results
! False true results
Non-Boolean logic operation results are not necessarily involved in value is a Boolean value
Implicit true: number other than 0, non-empty string
Implicit false: "", 0, NaN, undefined, null
Short circuit syntax:
a && b: if a is true, the result is B; if a prosthesis, the results of a
a || b: if a is true, the result is a; if a false result b
Operators
Math is a built-in object js
Math.random (): random number;: can not write; results are floating point numbers between 0 and 1
Math.pow (,): the power operation; parameters: a parameter index results in base two parameters are numerical results of calculated power
Math.sqrt (): root operation parameters: a parameter to prescribe the numerical results: prescribing value
Math.PI pi [pi] (Properties)
Comparison Operators
> Greater than
<Less than
> = Greater than or equal
<= Less than or equal
== equal
=== congruent
! = Not equal
! == equal to incomplete
(As long as the comparison operators, the result must be Boolean
- Boolean value when null involved in computing, implicit conversions. true (1) false (0) null (0), a special null participate == , === When not converting 0
- When implicit conversion is purely numeric string participate.
- == equal, the judge let both sides of the relationship on both sides as equal as possible. Only determined values are the same, judging whether the data type is not equal.
- === full equal, ranging as far as possible so that the relationship between both sides. And judges whether the same type and value
- ! = Not equal, and == is the opposite. ! == as long as is true, then it must be = false; as long as == is false, then = must be true!
- ! == equal incomplete, and === are opposites. ! === long as is true, then it must be == false;! === long is false, then it must be true ==
- Both sides are string comparisons, instead of comparing the length of the string, but more character Unicode. Encoded by the sequence, the greater the sequence: numbers (0-9), uppercase letters (AZ), lowercase letters (az)
Assignment Operators
Assignment operator is assigned a value of the operation based on the operand values to its right to its left. The simplest assignment operator is equal to (=), the operation of the right value assigned to the left operand. Then x = y is the value of y is assigned to x.
Meaning: The data on the right side of the operation after the assignment to the left .
+ = Equal plus
- = subtraction is equal to
* = Multiplication equal
/ = Equal except
% = Equal modulo
++ sliding scale
- decreasing
On the basis of the original variables, calculates the right side, the calculation of the value assigned to the variable on the left again.
1 // 声明变量
2 var a = 10, b = 20, c = 30;
3 var sum = (a ++) + (++ b) + (c ++) + (++ a);
4 /*
5 = 10 + 21 + 30 + (++ a) 第二次出现就是再次使用，再次使用都是自加1后的结果
6 = 61 + 12
7 = 73
8 */
9 console.log(sum);
10 console.log(a);
11 console.log(b);
12 console.log(c);
顺序：贴身的（! ++ --）→ 数学 → 比较 → 逻辑 → 赋值
1 /*
2 1优先级： 贴身，数学，比较(结果一定是布尔值)，逻辑(与，或)，赋值
3 2a++ :使用变量当前值参与运算，a第二次使用是自加1后的结果
4 3真：非0数字，非空字符串
5 a&&b:
6 a||b:
7 */
8 var a = 4;
9 var sum = 1 * (2 + 3) && a++ || 5 > 6 && 7 < 8 || 9;
10 /*
11 = 1 * (2 + 3) && 4 || 5 > 6 && 7 < 8 || 9;
12 = 5 && 4 || 5 > 6 && 7 < 8 || 9; 括号想加
13 = 5 && 4 || false && true || 9 数学比较
14 = 4 || false && true || 9 从左往右 a为真结果为b
15 = 4 || false || 9 a为假结果为假 与与或比较与优先级高
16 = 4 || 9 a或false a为真结果为真
17 = 4 a为真结果为真
18 */
19 console.log(sum);
20 // 第二次出现a = 5
21 console.log(a);
22 console.log(++ a);