Convert Object to Number.png

1.Object

[JavaScript]
/*** object.valueOf() 返回对象本身 ***/
var obj = {x: 1, y: 2};
obj.valueOf();    //=> {x: 1, y: 2}

obj = {};
obj.valueOf();    //=> {}

2.Array

[JavaScript]
/*** Array.valueOf() 返回对象本身 ***/
var arr = [1, 2, 3];
arr.valueOf();    //=> [1, 2, 3]

arr = [1];
arr.valueOf();    //=> [1]

arr = [];
arr.valueOf();    //=> []

3.Function

[JavaScript]
/*** Function.valueOf() 返回对象本身 ***/
var func = function (x) { return x + 1 };
func.valueOf();    //=> ƒ (x) { return x + 1 }

4.Date

[JavaScript]
/*** Date.valueOf()，返回1970.1.1以来的毫秒数 ***/
var dt = new Date();
dt.valueOf();    //=> 1523702519206

5.RegExp

[JavaScript]
/*** RegExp.valueOf() 返回对象本身 ***/
var reg = /\d+/g;
reg.valueOf();    //=> /\d+/g

实例1

[JavaScript]
//对象obj转换为Number类型
var obj = {x: 1, y: 2};
obj.valueof();    //=> {x: 1, y: 2}，非原始值
obj.toString();  //=> "[object Object]"，原始值
"[object Object]" => NaN

实例2

[JavaScript]
//数组arrj转换为Number类型
var arr = [1, 2, 3];
arr.valueOf();    //=> [1, 2, 3]，非原始值
arr.toString();  //=> "1,2,3"，原始值
"1,2,3" => NaN
-------------------------------
arr = [9];
arr.valueOf();    //=> [9]，非原始值
arr.toString();  //=> "9"，原始值
"9" => 9
-------------------------------
arr = [];
arr.valueOf();    //=> []，非原始值
arr.toString();  //=> ""，原始值
"" => 0

实例3

[JavaScript]
//函数func转换为Number类型
var func = function (x) { return x + 1 };
func.valueOf();    //=> ƒ (x) { return x + 1 }，非原始值
func.toString();    //=> "function (x) { return x + 1 }"，原始值
"function (x) { return x + 1 }" => NaN