短路运算符

js中的短路运算符主要是&&和||

&&

1.左边的值经过boolean运算为true，返回右边的值

eg:

var a= 1 && "bb";

console.log(a); //bb

2.左边的值为null、undefined或NaN，返回null、undefined或NaN

eg:

var a= null && "34343";

console.log(a); //null

3.左边的值经过Boolean运算为false，返回左边的值

eg:

var a= 1;

var b= a> 10 && a< 5;

console.log(b); //false

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||

1.左边的值Boolean运算为true，返回左边的值

eg:

var a= 5 || 6;

console.log(a);

2.左边的值Boolean运算为false，返回右边的值

var a= 1;
var b= a>6 || NaN;
console.log(b); //NaN

3.左边为null、undefined、NaN，返回右边的值

eg:

var b= NaN || undefined;
console.log(b); //undefined