What data types does ECMAScript have?

ECMAScript data types are divided into two types: 1. Basic data types, including String, Number, Boolean, undefined, null and Symbol types; 2. Reference data types, including Object, Function and Array types.

The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.

ECMAScript data types can be divided into two types: basic data types and reference data types

Basic types

Basic types are also called value types.

• String: Any string

• Number: Any number

• Boolean: true, false

• ## undefined: undefined

• null: null

• Symbol

##Object TypeObject type is also called reference type

Object: any object
Function: a special Object (difference from Object: can be executed)
Array: a special object (numeric subscript, internal data is ordered)

How to determine the type of datatypeof: can determine undefined, numerical value, string, Boolean value, function

cannot determine : null and Object, Object and Array

Returns the string expression of the data type.

instanceof: Determine the specific type of the object.
===: Can judge undefined and null

---

1. Basic type judgment method:

var a;
console.log(a);//undefined
console.log(typeof a);//"undefined"
console.log(a===undefined);//true
a=4;
console.log(typeof a==="number");//true
a='dewferf';
console.log(typeof a==='string');//true
console.log(typeof a==='String');//false
a=true;
console.log(typeof a === 'boolean');//true
a=null;
console.log(typeof a,a===null);//"object",true

2. Reference type Judgment method

var b1={
	b2:[1,'avc',console.log],
	b3:function(){
	console.log('b3');
	return function(){
		return 'lxyxxx';
	}
	}	
};
console.log(typeof b1.b2);//'object'
console.log(b1 instanceof Object,b1 instanceof Array);//true,false
console.log(b1.b2 instanceof Array,b1.b2 instanceof Object);//true，true
console.log(b1.b3 instanceof Function,b1.b3 instanceof Object);//true,true

console.log(typeof b1.b3);//'function'
console.log(typeof b1.b3 === 'function');//true

console.log(typeof b1.b2[2]);//'function'
console.log(typeof b1.b2[2] === 'function');//true
b1.b2[2](4);//因为b1.b2[2]是函数，所以会执行
b1.b3()();//

Symbol type

Symbol is a new data type introduced in ECMAScript6, which represents a unique value. Symbol type The value needs to be generated using the Symbol() function, as shown in the following example:

var str = "123";
var sym1 = Symbol(str);
var sym2 = Symbol(str);
console.log(sym1);          // 输出 Symbol(123)
console.log(sym2);          // 输出 Symbol(123)
console.log(sym1 == sym2);  // 输出 false ：虽然 sym1 与 sym2 看起来是相同的，但实际上它们并不一样，根据 Symbol 类型的特点，sym1 和 sym2 都是独一无二的

The parameters of the Symbol function only represent the description of the current Symbol value, so the return values ​​​​of the Symbol function with the same parameters are not equal. of.

#The new command cannot be used before the Symbol function, otherwise an error will be reported. This is because the generated Symbol is a primitive type value, not an object. That is,

Since Symbol values ​​are not objects, properties cannot be added. Basically, it is a string-like data type.

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