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
巴特西

二 js表达式与运算符

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