In JavaScript Variables can hold any data. JavaScript is a dynamically typed language, variables can arbitrarily change the data type:
1 let message = 'hello'; 2 lmessage = [1, 2, 3] 3 console.log(message); // [1, 2, 3]
JavaScript has a total of eight basic data types.
number type
represents an integer number type and a floating point number can have many operations, such as addition +, subtraction -, * multiplication, division / and the like.
Including three special values "Infinity" positive infinity, '' - Infinity "negative infinity," NaN "non-numeric.
Wherein NaN represents a calculation error is caused by incorrect or undefined mathematical operations come, and having a viscosity, i.e., if computation occurred a NaN, will lead to the final result is NaN.
1 let a = "hello"; 2 let b = 2; 3 console.log(a / 2); // NaN 4 console.log(a / 2 + 3); //NaN
BigInt type
Recently introduced until BigInt javascript type, it represents an integer of arbitrary length. Usually at the end of the integer field plus n to create BigInt.
1 // Appends BigInt n indicates that this is the type 2 const = 45687965412365478n BigInt;
Note: currently only compatible with Chrome and Firefox.
String type
JavaScript string must be enclosed in quotes.
. 1 the let str1 = 'Hello'; // single quotes 2 the let str2 = "Hi"; // double quotes . 3 ! = The let phrase `$ {} str1, str2} {$`;! // Backticks . 4 the console.log (phrase); // the Hello, hi!!
Single and double quotes are simply references, there is no difference.
Anti quotation marks are extensions, which allows only the variables and expressions will be packaged in $ {} string is embedded, for example:
. 1 the let name = "Neal" ; 2 the console.log ( "Hi, Neal $ {}"); // Hi, Neal $ {} . 3 // embedded variables . 4 the console.log (Hi `,` $ {name}) ; // Hi, Neal . 5 // embedded expression . 6 the console.log (IT apos `$ 12 is {+} now`. 1); // apos 13 is now IT
A Boolean (logical type)
Boolean type comprises two values true and false.
Boolean values can be used as a result of the comparison:
1 let isSmaller = 1 < 2; 2 console.log(isSmaller); // true
Itself also said is correct, true correct, false incorrect.
"null"
Most special null, does not belong to any one type of the above, it constitutes a separate type, only a null value, simply expressed as "no" empty "," or "value is unknown."
1 let image = null;
"undefined"
undefined is also a self-contained class that represents not assigned.
If a variable is declared, it has not been assigned, then its value is undefined:
1 let i; 2 console.log(i) // undefined
object type
is a special type of object, all other data types are "native type", because they contain only a single value of the content, storing object data set are used and complex entity.
We can create an object by using braces with an optional list of attributes {???}. A property is a key-value pair ( "key: value"), in which the key ( key) is a string (also called property
Name), value ( value) can be any value.
1 let obj = {name: "jack", age: 18}; 2 let obj2 = {country: "china", city: ["chengdu", "chongqing"]}; 3 let obj3 = {country: "china", province: {"sichuan": "chengdu"}};
symbol
symbol is an identifier representing the values are unique, can not be modified.
1 let s1 = Symbol(1); 2 let s2 = Symbol(1); 3 console.log(s1 === s2); // false