A brief analysis of operators and expressions in JavaScript

The following article will introduce you to the operators and expressions in JavaScript. I hope it will be helpful to you!

1. Expression

##1.1 Original expression

3.14  //数字直接量
"hello world"  //字符串直接量
/pattern/  //正则表达式直接量

true  //返回一个布尔值： 真
false  //返回一个布尔值： 假
null  //返回一个值： 空
this  //返回“当前”对象

i  //返回变量i的值
sum //返回sum的值
undefined  //undefined是全局变量，和null不同，它不是一个关键字

1.2 Expression

Operands and operators are combined.

1
1 + 2
(1 + 2) * 3
(1 + 2 ) * 3 && !flag

2. Operator

• Arithmetic operator(, -, *, /, %, ** ): Ordinary addition, subtraction, multiplication, division and remainder operations, where ** is the power operator.

 3 ** 2 // 结果为：9

• Unary operators (, --, , -): Some operators that require only one operand, Note the difference between : , -- when placed on the left and right sides of a variable. When placed on the left side of a variable, it increases (decreases) first and then takes the value. When placed on the right side, the opposite is true.

let a = 2, y, z;
y = ++a // 先执行a = a + 1, 得到 a = 3， 然后将a赋值给y，则y = 3
z = a++ // 接上面a = 3, 将a赋值给z，则z = 3，然后再执行 a = a + 1, 得到a = 4

//一元证号（+）
+3  //3
+'3'  //3
+true  //1
+functioan(a){return a}  //NaN

• Assignment operator (=, =, -=, *=, /=, %=): Change a constant Or assign the value of a variable or expression to another variable, Note: ES6’s new destructuring assignment.

//解构数组
let [a, b, c] = ['one', 'two', 'three']  // a = 'one', b = 'two', c = 'three'
//解构对象
let { name, age } = { name: 'cc', age: 100 }  // name = 'cc', age = 100

• Equality operator (==, !=, ===, !==): used to compare left and right operations Are the numbers equal? Please refer to: The matching rules of JS comparison operators ("===" and "==") and the judgment results of if() conditions.
• Relational operators (>, <, >=, <=): Used to compare the size of the operands around the operator.
• Bit operators(&, |, ~, ^, <<, >>, >>>): After the operand is converted into binary, operations such as AND, OR, NOT, XOR, etc. are performed, and finally a value in JS is returned. Among them, >>> is unsigned right shift.
• Logical operators (&&, ||, !): Mainly use AND, OR, NOT to determine whether the value of an expression is true. Note: AND and OR operations have a short-circuit calculation effect.

//短路计算
false && (anything) // 结果为false
true || (anything) // 结果为anything

//方法1： 设置x的缺省值
function test(x) {
	x = x || 100
}
test(10)  //x = 10
test()  // x = 100

// 方法2： ES6的方式
function test(x = 100) {
 ...
}
test(10)  //x = 10
test()  // x = 100

• Conditional operator(? :): The only operator in JS with 3 operands, generally used for if Use the short form of the statement.
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