Learn more about JavaScript's core ECMAScript

To get a better insight into how JavaScript works, you must first understand the core ECMAScript of JavaScript. ECMAScript variables can be divided into original values and reference values

Original type: Undefined,number,string,boolean,null.

Determining the type of a variable using the typeof operator may return "undefined", "Boolean", "string", "number", "Object", "function"

The following is a reference fragment:





6     
7     
8     
9     Window.alert (typeof StringType);  
     Window.alert (typeof Numbertype);  
One     Window.alert (typeof Booltype);    
12     
13     
     Window.alert (typeof null);   
     Window.alert (typeof Math);   

</script>

It's a special place. The TypeOf operator returns "Object" for a null value. This is actually an error in the initial implementation of JavaScript and is then used by ECMAScript. Now, NULL is considered a placeholder for an object, which explains the paradox, but technically it is still the original value.

Undefined type

Undefined type only one value is undefined