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In JavaScript, the basic data types include the following five numbers, strings, Boolean values, null values and undefined values. (ES6 adds a new Symbol type value, which will not be introduced in this article).
Number
Integer or floating point number
var numInt = 1; var numFloat = 1.1;
String
A string is a sequence of characters representing a text value
var stringSingle = 'a'; var string = 'abscmj';
Boolean value
true / false
var t = true; var f = false;
5. undefined
undefined indicates the attribute when the variable is undefined
var x; if (x === undefined) { console.log(1) //1 } // 这里 var a 等价于 var a = undefined
null
A special keyword indicating a null value
// foo不存在,它从来没有被定义过或者是初始化过: foo; "ReferenceError: foo is not defined" // foo现在已经是知存在的,但是它没有类型或者是值: var foo = null; foo; null
The difference between undefined and null
// typeof返回数据的类型 typeof null // "object" (因为一些以前的原因而不是'null') typeof undefined // "undefined"
null means "no object", that is, there should be no value there
undefined means "missing value" , that is, there should be a value here, but it has not been defined yet
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