(7) JavaScript learning notes-operators (continued)

I. assignment operators with operations

1. + = perform addition and value assignment operations

 
Total + = sales_tax; // equivalent to total = total + sales_tax;
 

Ii. Conditional Operators
1. Ternary Operators

 
Greeting = "hello" + (username! = NULL? Username: "there"); // equivalent to greeting = "hello"; if (username! = NULL) greeting + = username; else greeting + = "there ";
 

Iii. typeof Operator
1. Before an operation number, the returned value is a string, indicating the type of the Operation number;

2. the number returns "Number", the string returns "string", the Boolean Value Returns "Boolean", the object, array, and null return "object", and the function returns "function ", undefined is returned"

Iv. array and Object Access Operators
1. Use [] to access the elements of an array and use. To access the elements of an object;

2. the object on the left and an identifier (property name) On the right must be the direct volume name of the property or method of the object, and the type does not need to be specified.

 
Document. lastmodified; navigator. appname; frame [0]. length; document. Write ("Hello World ");
 

3. If [] is an array on the left, the right must be an integer.

Frames [1]; document. Forms [I + J]; document. Forms [I]. elements [J ++];
 

4. If [] is an object on the left, it should be a string expression on the right, which specifies an attribute of the object;

 
Document ["lastmodified"]; frames [0] ['length']; data ["Val" + I];