二 js表达式与运算符

/**
* Created by Administrator on 2017/12/14.
* 表达式与运算符
*/

//1.基本表达式 加减乘除
var a = 4;
a = 7/6;
var b = (a + 4)/2;
console.log(a);
console.log(b);
console.log("==========");
//end

//2.比较运算符 == != > < >= <=
console.log(a <= b);
console.log(a == b);
console.log(a != b);
console.log("==========");
//end

//3.逻辑表达式 逻辑与(&&)和逻辑或(||)
var ret = (a > 1) && (a < 2);
console.log(ret);
console.log(true && false);
console.log("==========");
//end

//4.字符串
a = 10;
b = 20;
var num_str = "" + a + b + true;
console.log(num_str); //1020true
num_str = a + b + true + "";
console.log(num_str); //31
console.log("==========");
//end

//5.简约表达式 += -= *= /= ++ --
var c = null;
a += c; //a = a + c
a -= c; //a = a - c
a *= c; //a = a * c
a /= c; //a = a / c
a = 10;
a++; //a = a + 1 先参与运算，最后自增
++a; //a = a + 1 先自增在参与运算
console.log(a);
a--; //a = a - 1 先参与运算，最后自减
console.log(a);
--a; //a = a - 1 先自减在参与运算

a = 4;
console.log(a++);
console.log(++a);
// end