Difference between String primitives and String object.

Learn about, in what way the string primitive and string objects are different in javascript.

We can create string in three ways,

1. var a = "first way"; // we can also use single quotes

2. var b = String("second way");

3. var c = new String("third way");

// also we can create using 

4. var d = a + '';

The 1 and 2 will create primitive string , where as 3 will create a String object. But we can call all the string methods on the primitive string created from 1 and 2 , when we call one of the String object method on primitive String the browser will automatically convert the primitive string into string object .

Check the type of the strings created using typeof operator

typeof a     // "string"

typeof b     // "string"

typeof c     // "object"

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The string primitive is always parsed, i.e(string literal are treated as source code) , where as the string object is evaluated into a single string .

String primitives and String objects also give different results when using eval().

Primitives passed to eval are treated as source code.

String objects are treated like other objects , and it returns the object.

var a = "12 + 12";

eval(a); // 24

var b = new String("12 + 12");

eval(a); "12 + 12"

So how we can use String object in eval ?

We can use valueOf() method in String object which will return the string as primitive value

var a = new String("12 + 12");

eval ( a.valueOf() ) // 24

This above concept works same for Numbers and Boolean.