A method of translating the operations between different types of data in JavaScript _javascript tips

JS in different types of basic data can be converted between, this conversion is a rule can be found, not arbitrary random. There are 5 basic types of data in JS: String, number, Boolean, null, undefined, where the type commonly used for calculation or comparison is the first three.

Conversion between the underlying data

Other types of conversion figures

Raw data type	Target type number
Undefined	NaN
Null	0
False	0
True	1
Number string	The corresponding number
A string that cannot be converted	NaN

Other types are converted to strings

Raw data type	Target type string
Undefined	Undefined
Null	Null
False	False
True	True
Digital	Numeric string

Addition between different types of underlying data, the data is first converted to number, and then converted to string (if there is a string type of data that participates in the operation)

Copy Code code as follows:

null + undefined//0+nan

Null + false//0+0

1 + true//1+1

1 + ' 1 '//' 11 '; Number added to string the result is a string

The result of 1 + 2 + ' 3 '//';(1+2 ' is then added to ' 3 '; Here we have to take each step apart separately to see if it turns out to be the same as the following.

1 + (2 + ' 3 ')//' 123 '; first op ' 3 ', then 1+ ' 23 '

' s ' + null//' snull '

' s ' + undefined//' sundefined '

' s ' + true//' strue '

1 + true + undefined + ' s '//1+1+nan+ ' s ' =2+nan+ ' s ' =nan+ ' s ' =nans

Object participates in addition and subtraction operations

Object participates in the underlying type data operation, which is first converted to the underlying type. Call its valueof method first, if it is not the underlying type, call its ToString method, or throw an error if the returned is not the underlying type. However, the date data is just the opposite

Copy Code code as follows:

To facilitate observation of the ToString and valueof methods for rewriting date

Date.prototype.toString = function () {
return 1;
}

Date.prototype.valueOf = function () {

return 2;
}

var a = new Date,
b = new Date;

A + b; Call tostring,1 + 1, and the result is 2.

Re-rewrite the ToString method

Date.prototype.toString = function () {

return {};
}

var c = new Date,
d = new Date;

C + D; Call the ToString method returns not the underlying type, then call valueof,2 + 2, and the result is 4

Rewrite the valueof method again
Date.prototype.valueOf = function () {

return {};
}

var e = new Date,
f = new Date;

E + F; Error

Changing the above example to object or other type can get the corresponding result, but call valueof first, then call ToString.

The magic effect of the ' + ' number

The data has a plus ' + ' before it can be converted to a number

Copy Code code as follows:

+ ' 1 ' +1/2

+ ' s ' +2/NaN

Note: The first time, the format is not good, many flaws, welcome everyone to shoot bricks