Javascript (二)：Primitive Datatype

Primitive(原生的) datatype stored in memory stack.It’s value is literally copied(字面值复制).Even if change the original(原始的) value,the copied value remians unchanged.

• string
• number
• boolean
• undefined
• null

When a primitive value is used as if it were an object created by a constructor, JavaScript converts it to an object in order to respond to the expression at hand,but then discards the object qualities and changes it back to a primitive value. In the code below, I take primitive values and showcase what happens when the values are treated like objects

    var pstr = “123”;
    pstr.toString();
    // pstr =>Object =>primitive

var pnum = 123;
pnum.toString();
// pnum =>Object =>primitive

var ostr = new String("123");
ostr.toString();
// ostr =>primitive

var onum = new Number(123);
onum.toString();
//onum =>primitive