JS对象属性和方法 函数编写 JSON操作 特殊操作说明
- 2017-06-15 22:21:00
- admin
- 原创 1752
一、JS对象属性和方法
1、JS中一切都是对象,字符串、数字、数组、日期,等等;
2、属性是与对象相关的值;
3、方法是能够在对象上执行的动作;
4、字符串属性length,字符串方法indexOf()、replace()、search();
二、函数编写
1、无返回值函数:function myFunction(var1,var2) { code; }
2、有返回值函数:function myFunction(var1,var2) { code; return ret; }
3、局部变量通过var关键字申明,不使用var关键字则为全局变量;
三、JSON操作
字典序列化:
var user = {name:'feinen', age:21};
console.log(user);
console.log(JSON.stringify(user));
数组序列化:
var cars=new Array();
cars[0]='Audi';
cars[1]='BMW';
cars[2]='Volvo';
console.log(cars);
console.log(JSON.stringify(cars));
序列化特详解:
var user;
console.log(JSON.stringify(user));
user = null;
console.log(JSON.stringify(user));
user = 21;
console.log(JSON.stringify(user));
var user = {name:'feinen', age:null, loc: undefined};
console.log(user);
console.log(JSON.stringify(user));
输出:
undefined
null
21
Object {name: "feinen", age: null, loc: undefined}
{"name":"feinen","age":null}
反序列化详解:
var user = '{"name":"feinen","age":null}';
console.log(JSON.parse(user));
user = null;
console.log(JSON.parse(user));
user = '';
console.log(JSON.parse(user));
user = '{';
console.log(JSON.parse(user));
user = undefined;
console.log(JSON.parse(user));
输出:
Object {name: "feinen", age: null}
null
SyntaxError: Unexpected end of input
四、特殊操作说明
取变量类型:
var name = 'feinen';
console.log(typeof name);
输出:
string
比较运算符:
1、字符串和数字比较,字符串自动转为数字;
2、字符串和字符串按照字典顺序比较;
3、其中一个表达式为NaN,返回false;
全等于还会比较类型:
var name = '5';
console.log(name == 5);
console.log(name === 5);
console.log(undefined == null);
console.log(undefined === null);
输出:
true
false
true
false
NaN或Number.NaN:
var num = Number.NaN;
console.log(num == num);
console.log(isNaN(num))
console.log(num);
console.log(typeof num);
输出:
false
true
NaN
number
比较运算null和undefined:
var num = 99;
console.log(num > null);
console.log(num == null);
console.log(num < null);
console.log(num > undefined);
console.log(num == undefined);
console.log(num < undefined);
true
false
false
false
false
false
var num = '99';
console.log(num > null);
console.log(num == null);
console.log(num < null);
console.log(num > undefined);
console.log(num == undefined);
console.log(num < undefined);
true
false
false
false
false
false
var num = 0;
console.log(num > null);
console.log(num == null);
console.log(num < null);
false
false
false
var num = -1;
console.log(num > null);
console.log(num == null);
console.log(num < null);
false
false
true