JavaScript determines whether the variable is an object or an array method _javascript tips

typeof all Return Object

All data types in JavaScript are strictly objects, but in practice we still have types, if we want to determine whether a variable is an array or an object using TypeOf, because it all returns object

Copy Code code as follows:

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:

Copy Code code as follows:

O typeof is Object
A typeof is Object

Therefore, we can only discard this method, to determine that there are two methods of array or object

First, use the TypeOf plus length property

The array has a length property, the object is not, and the TypeOf array and object are returned object, so we can judge

Copy Code code as follows:

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, using instanceof

Use instanceof to determine whether a variable is not an array, such as:

Copy Code code as follows:

var o = {' name ': ' Lee '};
var a = [' reg ', ' Blue '];

Alert (a instanceof Array); True
Alert (o instanceof Array); False

or whether it belongs to the object.

Copy Code code as follows:

var o = {' name ': ' Lee '};
var a = [' reg ', ' Blue '];

Alert (a instanceof Object); True
Alert (o instanceof Object); True

But the array is also object, so the above two are true, so we want to use instanceof to judge whether the data type is an object or an array, we should prioritize the array, and finally judge the object

Copy Code code as follows:

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:

Copy Code code as follows:

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 is also judged to be object.