What are the es6 data types?

es6 There are seven data types: 1. Boolean (Boolean type); 2. Null (empty type); 3. Undefined (unassigned type); 4. Number (numeric type); 5. String ( String type); 6. Symbol (unique type); 7. Object (object type).

The operating environment of this article: Windows 10 system, Vue version 2.9.6, DELL G3 computer.

What are the types of es6 data types?

es6t defines 7 data types: 6 primitive data types and 1 object type.

are:

• Boolean

• Null

• Undefined

• Number

• String

• Symbol

• Object

Detailed introduction:

1. One value data type: null, undefined

It is not necessary to display a custom variable is defined as undefined, but it does not work for null. That is to say: as long as the object is intended to be saved but the object has not been actually saved, the variable should be explicitly allowed to save the null value.

Mainly summarize the similarities and differences between the two:

Same points: both are data types of a value; both return false when participating in judgment; both have no methods

Differences: (a), null is an object, and undefined is not an object; (b), null is a keyword, and undefined is not a keyword; (c), null is 0 when converted to a number, and undefined is converted It is NaN when it is a number; (d), typeof null returns 'object', typeof undefined returns 'undefined';

alert(null == undefined) ;//true

2. The data type of the two values: boolean, that is, true and false

The main purpose is for judgment;

Under normal circumstances, only these six situations will turn false: empty string, null, undefined, 0, -0, NaN

How to convert an array into a boolean value can use two methods: Boolean(), !!()

3. Three value data types: number, that is, integer, float Points, NaN (personal classification, not important).

It is recommended when using numbers: try to use decimal, less hexadecimal, and no octal.

Do not compare data when using floating point numbers. 0.1 0.2 don't compare with 0.3. The reason is that computers use binary to represent data, and the binary representation of 0.1 plus the binary representation of 0.2 is not equal to the binary representation of 0.3.

There is a strange thing in number, which is not equal to itself. That is, alert (NaN == NaN) // false;

But NaN is a data type, which means the return value of typeof NaN is 'number';

For the above two features, ECMAScript A function isNaN() is provided; its purpose is to determine whether the incoming value can be converted into a number, and the return value is a boolean value.

The empty string converted to a number is 0;

To convert a value to a numeric type, you can use Number();

4. String String

Strings are generally represented by double quotes or single quotes. It is recommended to use single quotes to represent strings.

Characteristics of strings: Strings in ECMAScript are immutable, that is to say, once a string is created, its value will not be changed. If you change the value of the string, destroy the original string first. string, then fill the variable with a string containing the new value.

There are two ways to convert a value into a string type. One is to call the toString() method; the other is String();

Note: null and undefined do not have toString() method.

5. Symbol

There are two values ​​of Symbol. One is the original attribute name. One is the attribute name generated by Symbol(). Since its representation is unique, the attribute name will not conflict.

Note when using Symbol: the new operator cannot be used before the Symbol function (Symbol is a primitive data type, not an object); methods cannot be added to Symbol; symbol is a basic data type in the form of a string; symbol can Convert to string (two methods, already introduced before.), can be converted to boolean, but cannot be converted to Number.

When using Symbol(), it is best to pass in parameters. When no parameters are passed in, when using typeof, it will return 'symbol'. When adding parameters, it will return 'symbol (parameter)', which is easy to distinguish. ; Since the value of symbol is unique, even if the same parameter is passed in, the two values ​​​​are not equal.

Since the value of Symbol is unique, it can exist as an attribute name. However, as an attribute name, dot (.) operations cannot be performed. All Symbol values ​​are placed in square brackets ([]).

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