Typeof returns object

In JavaScript all data types are strictly objects, but in practice we still have types, and if you want to determine whether a variable is an array or an object you can’t use typeof because it all returns objects

var o = { 'name':'lee' };
var a = ['reg','blue'];
 
document.write( ' o typeof is ' + typeof o);
document.write( ' <br />');
document.write( ' a typeof is ' + typeof a);

Perform:

o typeof is object
a typeof is object

Therefore, we can only abandon this method, to determine the array or object there are two ways

First, use the typeof plus the length property

The array has a length property, object does not, and both the typeof array and the object return object, so we can say that

var o = { 'name':'lee' };
var a = ['reg','blue'];
 
var getDataType = function(o){
    if(typeof o == 'object'){
        if( typeof o.length == 'number' ){
            return 'Array';
        }else{
            return 'Object';   
        }
    }else{
        return 'param is no object type';
    }
};
 
alert( getDataType(o) );    // Object
alert( getDataType(a) );    // Array
alert( getDataType(1) );    // param is no object type
alert( getDataType(true) ); // param is no object type
alert( getDataType('a') );  // param is no object type

Second, use instanceof

Instanceof can be used to determine whether a variable is an array, such as:

var o = { 'name':'lee' };
var a = ['reg','blue'];
 
alert( a instanceof Array );  // true
alert( o instanceof Array );  // false

You can also determine whether it belongs to object

var o = { 'name':'lee' };
var a = ['reg','blue'];
 
alert( a instanceof Object );  // true
alert( o instanceof Object );  // true

However, arrays are also objects, so both of the above are true. Therefore, when we use instanceof to determine whether the data type is an object or an array, we should judge the array first and the object last

var o = { 'name':'lee' };
var a = ['reg','blue'];
 
var getDataType = function(o){
    if(o instanceof Array){
        return 'Array'
    }else if( o instanceof Object ){
        return 'Object';
    }else{
        return 'param is no object type';
    }
};
 
alert( getDataType(o) );    // Object
alert( getDataType(a) );    // Array
alert( getDataType(1) );    // param is no object type
alert( getDataType(true) ); // param is no object type
alert( getDataType('a') );  // param is no object type

If you don’t prioritize Array, for example:

var o = { 'name':'lee' };
var a = ['reg','blue'];
 
var getDataType = function(o){
    if(o instanceof Object){
        return 'Object'
    }else if( o instanceof Array ){
        return 'Array';
    }else{
        return 'param is no object type';
    }
};
 
alert( getDataType(o) );    // Object
alert( getDataType(a) );    // Object
alert( getDataType(1) );    // param is no object type
alert( getDataType(true) ); // param is no object type
alert( getDataType('a') );  // param is no object type

Then the array will also be judged as object.