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This article mainly explains "what is the original value of JavaScript object conversion". The content of the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn what the original value of JavaScript object conversion is.

Object.prototype.valueOf ()

The valueOf of an object is designed to return the original value of the object and is automatically executed where the object needs to be converted to the original value. More details here.

Object.prototype.toString ()

The toString () method returns a string representing the object, which is automatically executed where the object is expected to be converted to a string. The object's default toString () method returns [object type], and this type is the name of the object constructor. More details here.

Symbol.toPrimitive

The Symbol.toPrimitive (hint) method works the same as valueOf (), but takes precedence over valueOf (), and it also accepts a parameter, hint, that represents the specific type of original value you want to convert, in the following ways:

Number: numeric type

String: string type

Default: default

Let obj = {[Symbol.toPrimitive] (hint) {switch (hint) {case 'number': return 123; case' string': return 'str'; case' default': return 'default'; default: throw new Error ();} 2 * obj / / 2463 + obj / / '3default'obj = =' default' / / trueString (obj) / / 'str' object conversion original value

All three methods are triggered when the object is expected to be converted to some original value.

1. Expected to be converted to a string type

The corresponding hint type is string

Where the output is made, such as alert ()

String (obj)

Let a = {toString () {return'2'}} console.log (String (a)) / / 2

String concatenation (+) operation

Let a = {toString () {return'2'}} console.log (a + 'vv')

Template string

Let a = {[Symbol.toPrimitive] (hint) {console.log (hint) / / string return 2}} console.log (`are you the old ${a}? `) / / are you the boss? two。 Expected to be converted to a numeric type

The corresponding hint type is numbe

Division:

Let a = {valueOf () {return 2}} console.log (2 / a, a / 2) / / 1 1

Number (obj):

Let a = {[Symbol.toPrimitive] (hint) {console.log (hint) / / number return 2}} console.log (Number (a)) / / 2

Plus or minus sign (note that it is not an addition or subtraction operation):

Let a = {[Symbol.toPrimitive] (hint) {console.log (hint) / / number return 2}} console.log (+ a) / / 2console.log (- a) / /-23. Expected to be converted to the default type (other)

The corresponding hint type is default

Numeric addition (that is, the party added to the object is the numeric type):

Let a = {[Symbol.toPrimitive] (hint) {console.log (hint) / / default return 2}} console.log (1 + a) / / 3

This is a bit of a surprise. I thought that the type expected to be converted in this case should be a numeric type, but it is actually default.

Boolean operations: all objects are converted to true

Let a = {[Symbol.toPrimitive] (hint) {console.log (hint) / / No return false}} console.log (Boolean (a), a & & 123) / / true 123

Boolean operations include =

The trigger sequence of the three methods

First determine whether the object has a Symbol.toPrimitive (hint) method, and if so, execute the method, and if not, perform the following steps

If it is expected to be converted to a string type, the toString () method takes precedence

If you expect to be converted to the default type or numeric type, the valueOf () method takes precedence:

Note: if there is no valueOf () method, but the toString () method is defined, the toString () method will be executed

Thank you for your reading, these are the contents of "what is the original value of JavaScript object conversion?" after the study of this article, I believe you have a deeper understanding of what the original value of JavaScript object conversion is, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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